Alberto Odorizzi Luan

Odorizzi

Marlice Santos

Claire Botelho Costa

Odair Aparecido Lavigne

Armin Fernandes

Pierre P Bischoff

Franck

Santos

Marlic Botelho Costa

Claire Lavigne

• Odair

Aparecido Fernandes

Armin Bischoff

Pierre Franck
email: pierre.franck@inra.fr

Influence of the margin vegetation on the conservation of aphid biological control in apple orchards

Keywords: Hemiptera, Aphididae, Aphidophagous predators, Dysaphis plantaginea, Conservation biological control, Floral resources, Apple orchard

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The management of non-crop habitats in agricultural landscapes has received a considerable interest during the last decades as a way to conserve biodiversity and agricultural sustainability (e.g. [START_REF] Scherr | Biodiversity conservation and agricultural sustainability: towards a new paradigm of 'ecoagriculture' landscapes[END_REF]. The semi-natural vegetation in the farmland support shelter and resource provision for many arthropods and it can be manipulated to reinforce pest biological control (e.g. Landis et al. 2000;Gurr et al. 2017). The implementation of wildflower strips optimizing floral resource provisioning has been suggested to improve conservation biological control (Griffiths et al. 2008;Dib et al. 2012;[START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]. Such wildflower strips have positive effects on natural enemy abundance and associated ecosystem services [START_REF] Wyss | Biodiversity in organic horticulture-an indicator for sustainability and a tool for pest management[END_REF]Haaland et al. 2011;Balzan et al. 2014). Sugar resources from floral or extrafloral nectars significantly increase the fitness of many parasitoids and hoverfly species and, usually, their efficiency to control insect pests [START_REF] Wäckers | Assessing the suitability of flowering herbs as parasitoid food sources: flower attractiveness and nectar accessibility[END_REF][START_REF] Winkler | Nectar resources are vital for Diadegma semiclausum fecundity under field conditions[END_REF]Laubertie et al. 2012). The choice of plant species for wildflower strips needs to take into account the availability of pollen and nectar, the floral morphology, and the feeding preference of natural enemies [START_REF] Sivinski | Conserving natural enemies with flowering plants; estimating floral attractiveness to parasitic hymenoptera and attraction's correlates to flower and plant morphology[END_REF]Campbell et al. 2012;[START_REF] Wäckers | Pick and mix: selecting flowering plants to meet requirements of target biological control insects[END_REF]. Plants in field margins may also provide resources for insect pests and increase crop damage (Koji et al. 2007). Thus, plant species in wildflower strips need to be properly selected to favour natural enemies without increasing pest abundance (Lee and Heimpel 2005;Lavandero et al. 2006).

The rosy apple aphid (RAA), Dysaphis plantaginea Passerini (Hemiptera: Aphididae), is a major insect pest in apple orchards causing considerable damages, in particular fruit deformation (Blommers et al. 2004). Due to economic losses and socio-economic pressure to reduce pesticide applications, an increasing number of studies analyzed the efficiency of naturally occurring parasitoids and predators in controlling RAA populations (e.g. Albert et al. 2017). RAA is attacked by numerous generalist predator species such as spiders and earwigs (Dib et al. 2016;Lefebvre et al. 2017), and aphidophagous specialists such as hoverflies, ladybirds, and hymenopteran parasitoids [START_REF] Wyss | The effects of weed strips on aphids and aphidophagous predators in apple orchard[END_REF]Dib et al. 2010;Cahenzli et al. 2017). Among these RAA natural enemies, the most common species observed in south-eastern France were the hoverfly Episyrphus balteatus (De Geer) (Syrphidae), the ladybug Adalia bipunctata L. (Coccinelidae), the parasitoid Ephedrus persicae Froggatt (Braconidae) and the earwig Forficula auricularia L. (Forficulidae). No evidence of intra-or inter-specific competition on RAA prey was observed so far within these RAA natural enemy species [START_REF] Wyss | Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards[END_REF]Dib et al. 2016). Hoverflies and parasitoids depend on nectar and pollen and it was hypothesized that vegetation providing these resources may improve spring regulation of aphids in apple orchards (Markó et al. 2013;Miñarro and Prida 2013).

We designed a wildflower strip mixture comprising flowering species with different functional traits and life cycles (early to late flowering, annual to perennial, and various floral morphologies) in order to optimize floral resource provisioning. The effects of this wildflower strip mixture were compared with two different controls, spontaneous vegetation (SV) and grass strips. The effect of wildflower strips on the dynamics of the arthropod communities has usually been tested against the complete absence of noncrop vegetation [START_REF] Pfiffner | Impact of wildflower strips on biological control of cabbage lepidopterans[END_REF]Haaland et al. 2011;[START_REF] Tschumi | Tailored flower strips promote natural enemy biodiversity and pest control in potato crops[END_REF]). However, SV may be as efficient as flower strips in attracting natural enemies of insect pests (Denys and Tscharntke 2002) without producing costs for seed material and strip management. Sowing of grass strips may be a cost-efficient alternative providing habitat functions for natural enemies (Collins et al. 2002;Al Hassan et al. 2013). They provide less floral resources but generalist predators such as spiders, ground and rove beetles may benefit from their shelter function [START_REF] Wyss | The effects of weed strips on aphids and aphidophagous predators in apple orchard[END_REF]Collins et al. 2002). An efficient control of RAA requires a natural enemy movement from the field margins into the apple orchard. Most studies on wildflower strips are limited to observations of natural enemy diversity and abundance within the strips (Haaland et al. 2011;Blaauw and Isaacs 2014). The studies that analyzed the presence of natural enemies both in wildflower strips and within the crops usually confirmed the attraction of natural enemies by flowering plants but not always a corresponding reduction of insect pests [START_REF] Pfiffner | Use of sown wildflower strips to enhance natural enemies of agricultural pests[END_REF]Haaland et al. 2011). The few studies demonstrating a significant contribution of wildflower strips to pest control, showed that their contribution to pest control decreased with the distance to field margins (Collins et al. 2002;[START_REF] Tylianakis | Improved fitness of aphid parasitoids receiving resource subsidies[END_REF][START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]Albert et al. 2017). A better understanding of the spatial dynamics of natural enemies is needed to evaluate the efficiency of wildflower strips and to improve regulation of aphids in orchards.

In this study, we tested the influence of three margin strips (wildflower strips, grass strips, and SV) on the abundance of RAA and its natural enemies from the margin into apple orchard during two consecutive years in order to answer several unsolved questions: (I) Do wildflower strips optimized for nectar and pollen production increase natural enemy abundance in orchard margins in comparison with grass and SV strips? (II) Does the attraction of natural enemies by the flowering plants in the margins also increase their abundance inside the orchards? (III) Is the decrease in RAA abundance close to orchard margins presenting floral resources due to higher natural enemy density ?; (IV) Do orchard margin effects on natural enemy abundances and aphid control decrease with distance to the edge?

Materials and methods

Study sites and design

The experiment was set up in the three mono-cultivar apple orchards located at INRA Saint-Paul, Montfavet, France (43°54′51.57"N, 4°52′56.15"E). The two first orchards were contiguous, each comprising five rows of 24 apple trees planted in 1996 (cv Royal Gala or Granny). The third orchard, distant from the two first ones by 250-290 m, comprised six rows of 48 apple trees planted in 2004 (cv Ariane). A hedgerow parallel to the apple rows bordered the northern side of two orchards (cv Royal Gala and Ariane). A permanent grass sward was regularly mown largely limiting the presence of floral resources within each orchard. No pesticides were applied in any orchard during the study period that ran from March 2014 to June 2015. In March 2014, a 2.5 m wide and 40-80 m long margin was ploughed and then harrowed to remove weed seedlings emerging after ploughing. In each orchard, this margin was subdivided into three strips of equal size to establish the following three treatments (Fig. 1): (a) a wildflower strip mixture comprising 30 vascular plant species (WS; Table S1) optimized for a high and long lasting production of floral resources, (b) a grass strip (GS) including two perennial grasses, Lolium perenne L. (28%) and Festuca arundinacea Schreb (72%), used in France to sow buffer zones between field and water bodies to limit water pollution by fertilizer and pesticide drift, (c) an unsown strip allowing the natural development of SV. The minimum distance between the margin strips among the orchards was 40 m. The position of the strip treatments was randomized within each orchard margin. Thus, each orchard was considered to represent a replicate block. The approach to set up all treatments within the same orchard is relatively conservative since mobile arthropods may move between different strip types and the adjacent orchard, which may reduce the probability to find significant treatment differences. However, this design largely reduced confusion of the treatment effects with the influence of cultivar, plantation date or other environmental factors compared with designs that would apply each strip treatment in a different orchard.

Observations within margin strips

Plant species composition and provision of floral resources were evaluated in spring 2014 and 2015. First, plant richness was estimated based on the number of vascular plant species observed in each margin strip. Second, we calculated the percentage cover of flowering entomophilous plants as a proxy of floral resource provisioning. Percentage cover of all vascular plant species and proportion of vegetative, flowering and fruiting individuals of each plant species were recorded in each strip treatment at each orchard. We considered a plant species as entomophilous if indicated as insectpollinated in the BiolFlor database (Kühn et al. 2004). Percentage of each entomophilous plant was multiplied by the estimated proportion of flowering individuals at the respective survey date, which were added for all the entomophilous species to estimate the total percentage cover of flowering entomophilous plants in each margin strip. Survey dates were the 6 June 2014 and the 22 May 2015 corresponding to peaks of RAA abundance.

At the same dates, aphidophagous predators that were visible from outside the strip were counted during 10 min walking along each margin strip to evaluate the abundance of hoverfly and ladybug predators per margin strip. The entomological observations were limited to a period between 10:00 and 17:00 under favorable weather conditions (sunny, no rain, low wind speed).

Observations within apple orchards

Depending on orchard size, observations were performed on two or three labeled trees per treatment and per distance resulting in a total of 18 or 27 analyzed trees per orchard (Fig. 1). According to the position of the apple tree rows, the distances of the observed trees were 1, 5, and 17 m from the margin strips that are the main distances at which spillover from the margins occur (Brown and Lightner 1997). The same trees were observed twice a year at the end of April or the beginning of May (session 1) and 4 weeks later (session 2). Observations were performed at the tree and the RAA colony levels to calculate estimators of aphid infestation, change in aphid infestation between sessions, numbers of RAA natural enemies, and predation of sentinel aphids within the apple orchards.

First, the numbers of terminal growing shoots and of RAA colonies were counted in the canopy of each labeled tree. The terminal growing shoots were counted to take into account the apple tree vigor because mainly those shoots are attacked by RAA [START_REF] Simon | Aphids at crossroads: when branch architecture alters aphid infestation patterns in the apple tree[END_REF][START_REF] Rousselin | Rosy apple aphid abundance on apple is shaped by vegetative growth and water status[END_REF]. Aphid colony infestation per apple tree was calculated as the proportion of terminal growing shoots with a D. plantaginea colony. Aphid colony increment per apple tree was defined as the occurrence of trees with higher number of RAA colonies at session 2 than at session 1.

Second, three RAA colonies were randomly chosen at the northern and at the southern sides of each labeled tree (up to six colonies per tree). The number of aphids, mummies (dead bodies of aphids parasitized by braconid wasp) and aphid predators (mainly hoverflies, ladybugs, and earwigs) were recorded in each colony. Parasitism rate in the RAA colony was estimated as the ratio of the number of mummies on the total number of aphids assuming that parasitized and non-parasitized aphid were eaten at the same rates by the RAA predators. Occurrences per apple tree of each RAA natural enemy (aphid mummy or RAA predators) were estimated as their occurrences in at least one of the six colonies observed per tree.

Finally, sentinel aphids glued to sandpaper cards were used to evaluate potential aphid predation at tree level (Östman 2004). Three living aphids were attached to each 5 cm x 5 cm semi-rigid sandpaper card. The cards were fixed at the abaxial leaf surface of the observation trees to avoid sun exposition (1.5 m above the ground) and were removed the following day. Aphid predation was estimated as the proportion of sentinel aphids per card attacked during 24 h.

Statistical analysis

We used generalized linear models (glmer function, lme4 package, R version 3.2.4) to test: (1) the effect of the strip treatment on the number of vascular plant species, on the cover of flowering entomophilous plants, and on the abundance of aphid enemies in the orchard margins; (2) the effects of the strip treatment, of the distance to the orchard margin and the treatment x distance interaction on aphid infestation, aphid colony increment between session, occurrences of RAA natural enemies, and predation of sentinel aphids at apple tree level; (3) correlations between the number of aphids and the number of natural enemies at the RAA colony level. To take into account temporal variation, year and session (when relevant) were fitted as additional factors.

The plant species richness (number of vascular plant species) and the cover of flowering entomophilous plants (arcsin square root transformation of the percentage cover) were fitted using a Gaussian error distribution with identity link function. The abundance of natural enemies within margin strips was analyzed using a Poisson error distribution with log link function. Finally, the binary data of aphid infestation, aphid colony increment, predation of sentinel aphids and occurrence of mummies and RAA predators per apple tree were analyzed using a binomial error distribution with a logit function. Linear regressions were calculated to analyze relationships between the number of aphids (ln-transformed) and the total number of natural enemies (ln-transformed) within the RAA colonies.

Strip treatment (WS, GS, SV), distance to the margin strips (1, 5, and 17 m), year (2014 and 2015), observation date within year (session 1 and 2) and treatment x distance interaction were fitted as fixed factors. Orchard was included as a random factor in each model. In case of over-dispersion, an additional random factor (corresponding to the observation tree label) was included in the model (Harrison 2014). A reduced model only comprising strip treatment and year was applied to test observations within the margins.

The Anova and glht functions (car and multcomp R libraries, respectively) were used to test factors and the treatment x distance interaction (Wald's sequential probability likelihood ratio tests) and to compare the effects of a particular strip treatment and distance classes within each significant factor (Z-tests).

Results

Observations within margin strips

As expected, the cover of flowering entomophilous species and the number of vascular species significantly differed among the margin strips, but differences between years were not significant (Table 2). The cover of flowering entomophilous species was 2.5 fold higher on average in wildflower strips than in grass strips and in SV (Fig. 2A). No significant difference occurred between the SV and the grass strips. The number of vascular species per strip was also significantly higher in wildflower strips than in SV and grassy strips (Fig. 2B). On average, the wildflower strips presented ten more plant species than the other treatments.

Hoverflies and ladybugs, notably E. balteatus and A. bipunctata, were the most abundant aphid predators recorded in the margin strips. Hoverfly abundance differed significantly between years and strip treatments (Table 2). Hoverfly abundance increased from three individuals per strip on average in 2014 to 12 individuals per strip on average in 2015. The significant strip treatment effect was explained by a higher hoverfly abundance in the wildflower strips compared with grass and the SV strips (Fig. 3A,B). Ladybug abundance within margin strips (mean = 3.4 ± SD 4.4) did neither differ between years nor between treatments (Table 2).

Observations within the orchard on the apple tree

Inside orchards, ladybugs, hoverflies, and earwigs were the most frequently observed predators within the RAA colonies (Table 1). Lacewings, predatory bugs and spiders were only observed in a few colonies each year. Aphid mummies were only observed in the second spring session. The occurrence of all these RAA natural enemies per apple tree differed significantly between years and between spring sessions, but not among margin strip treatments, or among distance classes to the margin strip (Table 2). The occurrence of hoverfly larvae doubled between 2014 and 2015 (25-54% of the apple trees), but did not significantly differ among the strip 2; Fig. 3C,D). The occurrence of earwigs dramatically decreased between 2014 and 2015 (42-2% of the apple trees; Table 2). The occurrence of aphid mummies were slightly higher in 2014 than in 2015 (75 and 56% of the apple trees, respectively; Table 2).

On average, 18 RAA colonies were observed per tree and per date (Table 1). Aphid infestation was estimated as the proportion of terminal growing shoots carrying a RAA colony. The number of growing shoots per tree varied between years and between sessions, and marginally differed among the strip treatments (Table 2). Infestation by RAA was significantly different between years, sessions within years and distances from the margin strips (Table 2). Infestation by RAA was three times lower in 2015 than in 2014 (16 and 55% of the growing shoots, respectively). Infestation by RAA was significantly lower at 17 m than at 5 or 1 m from the margin strips (33, 37 and 36% of the growing shoots at 17, 5 and 1 m distances, respectively). The increment of RAA colonies was measured to evaluate variation of aphid infestation between sessions at the tree level. The proportion of apple trees with more RAA colonies at session 2 than at session 1 was marginally higher at the closest distances to the orchard margin strips (71, 74 and 62% of the apple trees at 1, 5 and 17 m distances respectively; Table 2).

On average, 25% of the sentinel aphids were preyed, but their predation was neither spatially structured within the orchards between distance classes, nor between margin strip treatments, nor temporally structured between sessions or between years (Table 2).

Observations within rosy apple aphid colonies

Very few aphids within RAA colonies were parasitized at the second session, but parasitism rate differed among the classes of distance (χ 2 = 20.2, df = 2, P = 4.0 × 10 -5 ). It was significantly lower at the closest distances to the orchard margin strips than at the 17 m distance (in average, 1.3 ± 0.7 and 3.2 ± 1.8%, respectively). Linear regressions between the number of aphids and the total number of their natural enemies in RAA colonies were used to test density-dependence effects of margin strip treatments. Numbers of natural enemies per RAA colony were significantly correlated to numbers of aphids (one natural enemy for 34 aphids on average; slope: χ 2 = 14.93, P = 1.1 × 10 -4 ; intercept: χ 2 = 5.04, P = 0.025). Separate linear regressions for each margin strip treatment were significant for the SV treatment (slope: χ 2 = 14.90, P = 1.1 × 10 -4 ) but not for the wildflower and grass strip treatments (Fig. 4). The intercept was only significantly different from 0 in the wildflower strip treatment (intercept: χ 2 = 4.28, P = 0.039; Fig. 4) indicating a higher availability of natural enemies in the absence of aphids.

Discussion

Our results showed that the selected wildflower strip mixture optimized for quantity and duration of nectar production was successful in increasing floral resource provisioning. The cover of flowering entomophilous plants species as a proxy for nectar and pollen production was significantly higher in wildflower strips than in grass and SV strips. Plant species richness was also higher although not all sown species developed in the wildflower strips. Only small differences occurred between grassy and SV strips but plant species richness in the grass strips was lower confirming the suppressive effect of competitive grass mixtures on spontaneously emerging species (Cordeau et al. 2012). SV emerging from the soil seed bank considerably contributed to both plant diversity and floral resources in both sown strips reducing the magnitude of treatment effects compared with other studies (Bischoff et al. 2016). Annual plant species were dominant during the first year but were replaced by biennials and perennials in the course of plant succession.

Among the two major aphid predators observed in the strips, only hoverflies responded to the strip treatment. Hoverfly densities were higher in the wildflower strips than in the other strips. Adult hoverflies rely on nectar resources [START_REF] Wäckers | Assessing the suitability of flowering herbs as parasitoid food sources: flower attractiveness and nectar accessibility[END_REF]Fiedler et al. 2008). Laboratory experiments on the aphidophagous hoverfly E. balteatus showed that adult fitness depends on floral resource provisioning (Laubertie et al. 2012). Markó et al. (2013) and Miñarro and Prida (2013) also found a positive effect of the surrounding vegetation on hoverfly abundance in orchards. Ladybirds did not respond to the strip treatments. Although occasionally feeding on pollen and nectar [START_REF] Triltsch | Food remains in the guts of Coccinella septempunctata (Coleoptera: Coccinellidae) adults and larvae[END_REF], their performance depends much less on floral resources because larvae and adults are predominantly predators [START_REF] Ricci | Migratory flight and pre-diapause feeding of Coccinella septempunctata (Coleoptera) adults in agricultural and mountain ecosystems of Central Italy[END_REF]). Nevertheless, several other studies found a positive effect of floral resources on ladybird abundance [START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]Bischoff et al. 2016).

The effect of strip treatments on natural enemies observed in aphid colonies inside orchards was not significant. The energetic costs and the relative attractiveness of margin strips may have reduced natural enemy movements into the orchard (Heimpel and Jervis 2005;[START_REF] Wanner | Tracing spatial distribution of parasitism in fields with flowering plant strips using stable isotope marking[END_REF]). However, hoverflies that strongly responded to the strip treatments are highly mobile insects. Hoverfly movements between the different treatment blocks may have reduced the probability to find significant treatment effects. Additionally, a time lag has to be considered between the measures of hoverfly abundance in wildflower strips and the occurrence of larvae in the orchards. Effects of resource provisioning on adult oviposition occur with a delay since larvae hatch after a couple of days and larvae feed for about three weeks on aphids (Laubertie et al. 2012;[START_REF] Van Rijn | Nectar accessibility determines fitness, flower choice and abundance of hoverflies that provide natural pest control[END_REF].

A combination of generalist predators, including some non-observed predators in the margin strips may contribute to a reduction of aphid infestation close to the wildflower strips (Balzan et al. 2014;[START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]. However, similarly to the natural enemies observed in the aphid colonies, the predation of sentinel aphids did not differ among the strip treatments neither among the classes of distance. Furthermore, the overall treatment effect on the aphid infestation was not significant. The lack of statistical power of our experiment because of a low number of replicated orchards and observations within each orchard treatment is a limitation to interpret such non-significant results. It seems that wildflower strips do not enhance aphid regulation to reduce spring RAA damages compared with less diversified plant strips, which is in agreement with previous observations in apple orchards on other aphid pests (Markó et al. 2013).

Aphid infestation and aphid colony increment were higher on apple trees close to the margin strips than on those that were inside the orchards. Inversely, the highest RAA parasitism rates were observed at the larger distances from the orchard margin. RAA secondary host during summer, Plantago lanceolata L. (Blommers et al. 2004), is a common species in the study region and was similarly abundant in all the strip treatments (6% of the total plant cover on average, Table S2). Although we did not observe any correlation between P. lanceolata cover and aphid infestation in margin strips (Table S2), it is possible that field margins represent a source of RAA infestation counteracting potential positive effects of strip treatments mediated by higher natural enemy densities.

In both years, a rapid and significant increase of aphid infestation was observed resulting in a high increment of aphid colonies and suggesting a relatively low natural regulation potential during early spring. Such a strong and rapid increase of aphid infestation was also observed in a previous study of RAA dynamics in orchards of the same region (Dib et al. 2010). An efficient biological control would require the presence of a sufficient number of natural enemies in March and April when the number of aphids per RAA colony is still low (Lefebvre et al. 2017). Most wildflower strip species started to flower later than April. In order to provide floral resources in time, a higher proportion of early flowering plant species would be necessary for controlling the exponential development of the RAA colonies. Early flowering species such as the arable annuals Veronica hederifolia, Sinapis arvensis and Capsella bursa-pastoris and the perennials Ajuga reptans and Bellis perennis were included in our wildflower strip mixture but their cover was low (Table S1). Similarly, late flowering species in autumn may increase the number of web spiders in the apple orchard [START_REF] Wyss | The impact of spiders on aphid populations in a strip-managed apple orchard[END_REF], which may contribute to reduce aphid damage by catching RAA elates when they migrate back to their primary apple host (Cahenzli et al. 2017). Such autumnal biocontrol may partially explain the reduction of RAA infestation between the two studied years.

We found a positive relationship between aphid colony size and natural enemy density indicating that natural enemies within orchards mainly responded to the available amount of prey or hosts. However, natural enemy numbers did not significantly depend on aphid numbers in the wildflower strip treatment. In absence of aphids, the regression model predicted higher natural enemy densities for the wildflower strip treatment than for the other treatments (regression intercepts), which may be the result of a higher spill-over of natural enemies from the wildflower strip. A relatively high mobility of natural enemies attacking aphid colonies may compensate for a lower spill-over of natural enemies in the other strip treatments.

In conclusion, we found positive effects of wildflower strips on floral resource provisioning increasing the abundance of hoverflies as important natural enemies of RAA in apple orchards. However, the effect of wildflower strips on aphid control was less strong than in studies using annual crops as model system [START_REF] Pfiffner | Impact of wildflower strips on biological control of cabbage lepidopterans[END_REF][START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]. Such differences may be partially due to differences in the experimental design. Most of the studies performed in annual crops have used less attractive controls than we did to evaluate wildflower strip effects (absence of vegetation, crop strips), increasing the probability to obtain significantly positive results (Haaland et al. 2011;[START_REF] Tschumi | High effectiveness of tailored flower strips in reducing pests and crop plant damage[END_REF]. However, differences in insect abundances between wildflower strips and other margin types also depend on the age of the wildflower strips and the time of the year (Haaland et al. 2011). However, we are convinced that a successful conservation biological control approach needs to provide a significantly better control service than spontaneously occurring vegetation to justify higher sowing and management costs. In order to improve pest regulation by wildflower strips, sowing inside orchards should be considered in order to reduce the distance of movements required to reach the target pest species (Albert et al. 2017). Our study also demonstrated the importance of temporal dynamics and the need to provide floral resources at the beginning of the season for an early control of the RAA colonies. Future studies should focus on natural enemy and aphid movements including their temporal dynamics to improve our understanding of interactions between natural enemies and RAAs and to evaluate the efficiency of wildflower planting in orchard margins.

Fig. 1

 1 Fig. 1 Experimental design. Shaded symbols indicate observation trees at three distance classes (1, 5 and 17 m) from the orchard margin treatments

Fig. 2 Fig. 3

 23 Fig. 2 Mean (± SE) cover of entomophilous flowering plants (A, B) and number of plant species (C, D) in 2014 (A, C) and in 2015 (B, D) in each orchard margin treatment; WS wildflower strip, SV spontaneous vegetation strips, GS grass strip. Different lowercase letters above columns indicate significant differences at p < 0.05

Fig. 4

 4 Fig. 4 Relationship between the number of aphids (RAA) and the number of natural enemies (NE) per aphid colony at the second 2015 session (ln-transformed values). Regression lines are presented to illustrate slope and intercept differences between WS (wildflower strip, white circles), SV (spontaneous vegetation strips, grey circles), and GS (grass strip, black circles) treatments. Stars indicate slopes or intercepts that significantly differ from zero (*P < 0.05; ***P < 0.001)

Table 1

 1 Mean number of D.

	plantaginea colonies (aphid		2014		2015
	colonies) and mean occurrence		6 May	3 June	24 April	19 May
	of RAA predators (hoverflies, ladybirds and earwigs) or aphid	Aphid colonies	19.9 [15.3-24.6]	41.9 [31.8-56.0]	1.5 [1.5-1.6]	22.3 [11.3-27.
	mummies (parasitized aphids)
	per apple tree in 2014 and
	in 2015
		Minimum and maximum values per orchard are indicated in brackets

Table 2

 2 Temporal and spatial variation at the apple tree level of aphid infestation (proportion of terminal growing shoots with at least one

		1), number of growing shoots, sentinel aphid predation and natural
		enemy occurences. Temporal and spatial variation in orchard margins
	D. plantaginea colony), aphid colony increment (occurrence of a	of plant species richness, cover of flowering entomophilous plants
	higher number of D. plantaginea colonies at session 2 than session	and hoverfly and ladybird abundances

Acknowledgements This work was supported by the PEERLESS project (ANR-12-AGRO-0006), by the Agropolis Fondation (ANR-10-LABX-0001) and by the "Structure Fédérative de Recherche" TER-SYS. We are also grateful to Elise Thenoux, Claire Estellon and Cécile Thomas for field assistance and data compilation.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Research involving human and animal participants This work does not include experiment with any animal or human subjects performed by any of the authors.

Al Hassan D, Georgelin E, Delattre T, Burel F, Plantegenest M, Kindlmann P, Butet A (2013) Does the presence of grassy strips and landscape grain affect the spatial distribution of aphids and their carabid predators? Agric For Entomol 15:24-33 Albert L, Franck P, Gilles Y, Plantegenest M (2017) Impact of agroecological infrastructures on the dynamics of Dysaphis plantaginea Passerini (Hemiptera: Aphididae) and its natural enemies in apple orchards in northwestern France.


Luan A O Santos

Armin Bischoff

Odair A Fernandes

The effect of forest fragments on abundance, diversity and species composition of predatory ants in sugarcane fields

Keywords: Predatory ants, Biodiversity, Biological control, Habitat fragmentation, Atlantic rain forest

Habitat loss and fragmentation have gradually caused loss of diversity and consequently the decline of ecological services. This study aimed to evaluate the effect of tropical forest fragments as natural habitats (river valley fragments and plateau fragments) on the community of predatory and omnivorous ants in nearby sugarcane fields. Twenty fields adjacent to these fragments were selected and evaluated one (dry season) and four months (rainy season) after harvest. In each field, ants were sampled in five linear plots (10 m inside the fragment, 0 m (field path between field and fragment), 5 m, 50 m and 100 m inside the crop fields). Each plot comprised ten sardine baits in a row parallel to the field edge. Species richness and frequency of ant species decreased with increasing distance from the forest fragments. Inside fields, species richness and frequency were higher during the period of vegetative growth (rainy season) than after harvest (dry season). Ant communities of sugarcane fields and forest fragments were more similar later in the season than directly after sugarcane harvest suggesting recolonization of the fields from the fragments. Several ant species were limited to forest fragments after harvest but occurred later in the season also in sugarcane fields confirming the potential contribution of fragments to the recolonization process and therefore to biological control of sugarcane-dominated pest insects.

Introduction

Agricultural production has been intensified during recent decades resulting in large areas of monocultures, and consequently, in a loss of natural and semi-natural areas and in an increased use of agrochemicals [START_REF] Tscharntke | Landscape perspectives on agricultural intensification and biodiversity-Ecosystem service management[END_REF][START_REF] Kennedy | A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems[END_REF]. With the increase of crop fields, semi-natural habitats have also been increasingly fragmented [START_REF] Tscharntke | Landscape moderation of biodiversity patterns and processes-Eight hypotheses[END_REF]) causing a rapid reduction of species interactions and ecological services [START_REF] Tylianakis | Global change and species interactions in terrestrial ecosystems[END_REF]. The resulting loss of biodiversity [START_REF] Pimm | Biodiversity: Extinction by numbers[END_REF] has led to a simplification and homogenization of plant and animal communities, affecting the stability of natural and agricultural ecosystems [START_REF] Mckinney | Biotic homogenization: A few winners replacing many losers in the next mass extinction[END_REF]. In large-scale monospecific agrosystems, Prasifka, Heinz, and L.A.O. Santos et al. / Basic and Applied Ecology xxx (2017) xxx-xxx [START_REF] Prasifka | Crop colonization, feeding, and reproduction by the predatory beetle, L.A.O. Santos et al. / Basic and Applied Ecology xxx (2017) xxx-xxx Hippodamia convergens, as indicated by stable carbon isotope analysis[END_REF] showed that losses in plant diversity have a negative effect on the composition and stability of arthropod populations.

Species diversity is heterogeneously distributed in different habitats, landscapes, and regions [START_REF] Rosenzweig | Species diversity in space and time[END_REF]. The factors that allow this heterogeneity are variable and depend on the scale of the analysis and the studied organisms [START_REF] Boehning-Gaese | Determinants of avian species richness at different spatial scales[END_REF][START_REF] Rahbek | The role of spatial scale and the perception of large-scale species-richness patterns[END_REF][START_REF] Fahr | Biome transitions as centres of diversity: Habitat heterogeneity and diversity patterns of West African bat assemblages across spatial scales[END_REF]. [START_REF] Tews | Animal species diversity driven by habitat heterogeneity/diversity: The importance of keystone structures[END_REF] found that structurally complex habitats support greater species richness because they provide more ecological niches including available resources (habitat heterogeneity hypothesis). Consequently, the distribution of beneficial arthropods in agricultural landscapes has also consequences for biological control services in various agricultural crops. Morever, the movement of these beneficials between patches is a spreading-risk strategy necessary for their own survival as well as for their progeny.

In Brazil, sugarcane dominated agricultural landscapes represent such an example of large-scale intensive agriculture with few semi-natural habitats. In our study area (São Paulo state), large crop fields are only interrupted by relatively small fragments of the former Atlantic rain forest either along river valleys (gallery forests) or on slopes and plateaus. In addition, the need for larger areas and higher sugarcane production has recently led to the expansion of sugarcane to former citrus orchards and extensive pasture. Information on the contribution of these forest fragments to the biological control of insect pests in agro-ecosystems is scarce.

Ant species are important natural enemies of insect pests in sugarcane and thus contribute to biological control. In the US, the invasive fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) contributes to the regulation of the sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera Crambidae) [START_REF] Adams | Interrelationship of ants and the sugarcane borer in Florida sugarcane fields[END_REF][START_REF] Choate | Ants as biological control agents in agricultural cropping systems[END_REF]. The ant species does not occur in our study area but [START_REF] Rossi | Ant predation of larval Diatraea saccharalis Fab. (Lep., Crambidae) in new sugarcane in Brazil[END_REF] found that generalist ants contribute to the reduction of sugarcane infestation by the sugarcane borer in the Brazilian state of São Paulo. A previous study showed that ants may consume up to 70% of D. saccharalis eggs in sugarcane fields, greatly reducing pest population densities (Santos, unpublished data). When evaluating the myrmecofauna in sugarcane fields of the same region, [START_REF] Rossi | Predaceous ant fauna in new sugarcane fields in the state of São Paulo, Brazil[END_REF] found that Solenopsis was the predominant ant genus. Even non-herbivorous ant species may have negative effects on crop plants if they co-occur with hemipteran pest insects providing honeydew [START_REF] Choate | Ants as biological control agents in agricultural cropping systems[END_REF]. However, in most cases such anthemipteran interactions are beneficial for crop plants since ants attack other more harmful pests [START_REF] Styrsky | Ecological consequences of interactions between ants and honeydew-producing insects[END_REF]. Ant colonies of sugarcane fields are strongly reduced by agricultural practices such as soil tillage and, consequently, re-colonization from outside the fields is required to re-establish populations after sugarcane plantation [START_REF] Choate | Ants as biological control agents in agricultural cropping systems[END_REF]. Semi-natural structures are known to provide resources and other habitat functions for ant species [START_REF] Offenberg | Review: Ants as tools in sustainable agriculture[END_REF]. Thus, it can be assumed that forest frag-ments in sugarcane-dominated landscapes play an important role in such re-colonization processes.

In the present study, we analyzed spatial distribution patterns of predatory ant species along gradients from forest fragments into sugarcane fields. We hypothesized that (1) predatory ant species are more frequent close to forest fragments providing shelter and resources and that their abundance decreases with distance; (2) ant species that colonize sugarcane fields can also be found inside fragments, confirming the hypothesis of potential colonization of field from fragments; (3) ant communities differ between river valley and plateau fragments but distance effects are similar.

Materials and methods

Study sites

The study was carried out in sugarcane plantations located near forest fragments in the Jaboticabal municipality of São Paulo state in Southeastern Brazil (Fig. 1). The climate is characterized by subtropical-mesothermic, dry winter and a rainy summer season, with an annual rainfall of 1285 mm, a mean temperature of 22 • C, and a mean relative humidity of 70.6%. The study area is located in a transition zone between Atlantic rain forest (Mata Atlantica) and the drier savannah systems (Cerrado).

Ants were sampled in twenty different sugarcane fields and in adjacent forest fragments, nine of which were located on plateaus and slopes (plateau fragments) and eleven close to rivers and creeks (river valley fragments, Fig. 1). Plateau fragments are often disturbed, with a higher cover of shrub and liana species compared to river valley fragments. River valley fragments as remnants of gallery forests are under national protection (Permanent Preservation Areas, PPA) to improve water quality of catchment areas. Afforestation of gallery forests is quite common in the study area resulting in a lack of older trees. Moreover, there are also differences in abiotic factors compared with plateau fragments (soil humidity, microclimate). The distance between collection fields was at least 500 m and average field size was 10 ha. Sugarcane was harvested mechanically and the straw (chopped leaves and stalk tips) was left on the soil. No insecticides were applied during the study period.

Design and measurements

At each selected site, a transect was set up from inside the forest fragment to a distance of 100 m into the sugarcane field.

Ants were sampled at five different distances along the transect. Field paths usually separating forest fragments and crop were used as the 0-m line. Sampling inside the fragments was performed at a distance of 10 m from this 0-m line. Inside the sugarcane field, ants were sampled at distances of 5 m, 50 m, and 100 m. Sampling was carried out using bait traps that specifically attract carnivorous and omnivorous but not herbivorous ants [START_REF] Fonseca | Riqueza de formigas (Hymenoptera, Formicidae) epigéicas em povoamentos de Eucalyptus spp. (Myrtaceae) de diferentes idades no Rio Grande do Sul, Brasil[END_REF]. As a bait trap we used five grams of canned sardines that were exposed on paper napkin (20 × 20 cm). At each distance, ten bait traps were placed every 10 m along a line parallel to the field edge resulting in a total of 50 traps per transect. After 30 min of exposure, baits and attracted ants were put into plastic bags and transferred to the lab. Ants were sorted by species and all samples were stored in 80% alcohol before final identification. Sampled ants were identified to species, although in some cases a number was given to species instead of a full name using a reference collection [START_REF] Suguituru | Formigas do Alto Tietê[END_REF]. Ants were sampled twice: one month after sugarcane harvest at the end of the dry period (October 2014), and four months later during the rainy season corresponding to the middle of the growing season (January 2015).

Statistical analysis

Linear models including distance as continuous factor and fragment type as a categorical factor were tested. Both factors were considered as fixed. A repeated measures design was applied using date as repeated measures factor and including all factor × date interactions. Normality and homoscedasticity were tested before analysis. Analyses were performed using PROC MIXED (SAS Institute, Cary, NC, USA). In the case of significant interactions between distance and the two fixed factors, separate regressions were calculated for date and fragment type to analyze the relationship between distance and ant diversity or abundance. We fitted the number of ant species at each distance (over ten bait traps) and the number of traps per distance occupied by each ant species (ant frequency) as response variables. Frequency values used as abundance estimates can reach a maximum value of ten if a species was found in all bait traps at a given distance. In order to analyze biodiversity changes along transects, ␤ diversity was calculated as the difference between ␥ diversity and mean ␣ diversity at each transect site. ␤ diversity was adjusted for ␥ diversity to account for different ␥ diversity levels in the dry and rainy season [START_REF] Anderson | Navigating the multiple meanings of ␤ diversity: A roadmap for the practicing ecologist[END_REF]. Again, a repeated measures model was fitted to compare fragment type effects at the two sampling dates and to evaluate the fragment type × date interaction.

Multivariate statistics was used to compare predatory ant communities along transects and between sampling dates in more detail. The models were run in Canoco 5 [START_REF] Smilauer | Multivariate analysis of ecological data using CANOCO[END_REF]. Following Canoco 5 adviser, we used unimodal DCA instead of linear methods since gradient length was higher than four standard deviations. Due to the leftskewed distribution, data were log(x + 1) transformed prior to analysis. No down-weighting was applied but only the ten species of ants with the highest weight were included in the biplots. Because differences between forest types were small, samples from gallery and plateau forest fragments were not separated in biplots.

Results

In total, 40 ant species belonging to 14 genera were collected (Appendix Table S1 in Supplementary material). The S1 in Supplementary material). After harvest, we found seven species only in forest fragments and three species only in sugarcane fields whereas fifteen species were common to both habitats. Three months later, three species were exclusive to the fragment areas and eight species were exclusive to sugarcane whereas 21 species occurred in both habitats. The species richness of ants was negatively related to the distance from the forest fragments (Table 1, Fig. 2). However, the significant distance × fragment type × date interaction indicated that the distance effect depended on season and fragment type. The distance effect was stronger after the harvest (dry season) than three months later (rainy season) and this was more evident at plateau than at river valley sites. However, the species richness-distance relationship showed a unimodal pattern at the first sampling date in river valleys. Species richness was generally higher close to river valley fragments than close to plateau fragments. The harvest date main effect was significant with lower species richness after sugarcane harvest. The mean ␤ diversity indicating ant community differentiation along transects was not different between fragment types and dates when adjusted for differences in ␥ diversity (Table 1). The mean ␥ diversity significantly increased from the first to the second sampling date (F 1,36 = 8.38, P = 0.0064).

The frequency of ants decreased with distance from forest fragments but the distance effect was only significant at P = 0.09 (Table 1, Fig. 3). Interactions with time and fragment type were not significant indicating that distance effects on frequency are more stable than those on species richness. Again, the date effect was significant with a much higher fre-quency four months after harvest whereas fragment types did not influence overall ant frequency.

Do. brunneus and Ph. oxyops were the most abundant species. The distance effect was significant in both species and could be explained by a decrease in frequency with distance from forest fragments (Table 1). The interactions with sampling date and fragment type were not significant confirming the consistent effect of distance on the dominant species. A higher frequency of Do. brunneus was observed at the second sampling date (rainy season), whereas differences between dates were not significant for Ph. oxyops.

The DCA biplots showed a large overlap of ant communities in forest fragment and sugarcane fields (Fig. 4). However, one month after harvest (Fig. 4A), ant communities were more separated between forest fragments and sugarcane fields than four months after harvest (Fig. 4B). At the first date, forest fragment samples were concentrated in the upper right part and sugarcane samples in the lower left part of the biplots. At the second date, this partial separation disappeared, suggesting a movement of ant species that were related to one of the habitats at the first date. Pheidole radeskowskii Mayr, 1884 and Camponotus crassus Mayr, 1862 occurred at the first date together with forest fragments sites in the upper right part suggesting a preference for this habitat. Both species occurred within sugarcane site polygons at the second sampling date suggesting a colonization from forest fragments into sugarcane fields. In general, the variation between communities largely decreased from the post-harvest to the growing season date.

Discussion

We found a reduction in ant species richness and frequency with increasing distance from forest fragments. Forest fragments comprise a higher variety of plant species providing floral and extra-floral nectar, litter, and branches, which strongly affects the diversity of ant communities. Thus, the greater variability in spatial structure, food and nesting resources may have led to a higher amount of ant species in these habitats [START_REF] Mezger | Partitioning the impact of abiotic factors and spatial patterns on species richness and community structure of ground ant assemblages in four Bornean Rainforests[END_REF][START_REF] Saad | Vinasse and its influence on ant (Hymenoptera: Formicidae) communities in sugarcane crops[END_REF]. Vegetation structure of agroecosystems is less diverse, not allowing a high diversity of ant species [START_REF] Offenberg | Review: Ants as tools in sustainable agriculture[END_REF]. In addition, the presence of trees may provide greater soil coverage, protection against high temperatures and lower humidity variation favoring ant species [START_REF] Gomes | Resposta da comunidade de formigas aos atributos dos fragmentos e da vegetac ¸ão em uma paisagem da Floresta Atlântica Nordestina[END_REF]. These habitat features may influence dominance structure of ant communities and allow the existence of higher ant species numbers in forest fragments [START_REF] Perfecto | Understanding biodiversity loss in agroecosystems: Reduction of ant diversity resulting from transformation of the coffee ecosystem in Costa Rica[END_REF][START_REF] Perfecto | Microclimatic changes and the indirect loss of ant diversity in a tropical agroecosystem[END_REF]. Our data confirm the results of several other studies showing that forest fragments are important to maintain ant and other arthropod diversity in agricultural landscapes [START_REF] Lucey | Tropical forest fragments contribute to species richness in adjacent oil palm plantations[END_REF][START_REF] Gray | Are riparian forest reserves sources of invertebrate biodiversity spillover and associated ecosystem functions in oil palm landscapes?[END_REF] although spill-over effects from fragments into fields were not always very strong [START_REF] Lucey | Spillover of insects from rain forest into adjacent oil palm plantations[END_REF][START_REF] Gray | Do riparian forest fragments provide ecosystem services or disservices in surrounding oil palm plantations?[END_REF][START_REF] Gray | Are riparian forest reserves sources of invertebrate biodiversity spillover and associated ecosystem functions in oil palm landscapes?[END_REF].

The species Cr. quadriformis, Do. brunneus, Ph. oxyops, Ph. radoskowski, and Pseudomyrmex termitarius (Smith, 1855) were frequent in forest fragments and sugarcane fields. Pheidole oxyops was a dominant species in both habitats whereas Do. brunneus was particularly dominant in sugarcane fields. Agroecosystems are intensively managed without decomposing trunks or trees, limiting potential nesting sites and therefore ant diversity [START_REF] Armbrecht | Enigmatic biodiversity correlations: Ant diversity responds to diverse resources[END_REF]. In addition, the high competitiveness of these two ant species may further limit ant species richness in crops (Holldobler & Wilson 1990;[START_REF] Andersen | A global ecology of rain forest ants: Functional groups in relation to stress and disturbance[END_REF]. Dorymyrmex species are very competitive in disturbed [START_REF] Hölldobler | The ants[END_REF][START_REF] Andersen | Functional groups and patterns of organization in North American ant communities: A comparison with Australia[END_REF][START_REF] Majer | Long-term recolonization patterns of ants in Western Australian rehabilitated bauxite mines with reference to their use as indicators of restoration success[END_REF]) and open [START_REF] Cuezzo | The ant genus Dorymyrmex Mayr (Hymenoptera: Formicidae: Dolichoderinae) in Colombia[END_REF] habitats, which explains their high abundance in crop fields compared with forest remnants. Do. brunneus is abundant in sugarcane fields [START_REF] Souza | Ant diversity in a sugarcane culture without the use of straw burning in south-east, São Paulo, Brazil[END_REF] and is an important predator of the sugarcane borer D. saccharalis.

The relatively high overlap of ant species captured in forest fragments and in sugarcane fields indicated that these natural habitats are potential refuges of ant species regulating pest insects in sugarcane fields during unfavorable environmental periods such as harvest or soil tillage. Differences between fragments and sugarcane fields were larger in October after disturbance by sugarcane harvest than later in the growing season. This difference did not result in significant changes in ␤ diversity between these two sampling dates, showing that community shifts based on presence/absence of species were not very strong. However, multivariate analyses taking into account ant frequencies separated ant communities of sugarcane fields after disturbance by sugarcane harvest whereas three months later this separation disappeared. In the postharvest period, the number of ant species occurring in both habitats was lower than later in the season. Three months later most species limited to forest fragments in the first survey were also found in sugarcane fields. Litter cover increasing with crop growth may have favored re-colonization by ant species [START_REF] Silva | Do leaf-litter attributes affect the richness of leaf-litter ants[END_REF]. The contribution of forest fragments to diversity and abundance of arthropods in adjacent crop fields and to related ecosystem services have been demonstrated in several studies (Klein et al. 2006;Gray & Lewis 2012;[START_REF] Lucey | Spillover of insects from rain forest into adjacent oil palm plantations[END_REF] including ant communities [START_REF] Lucey | Tropical forest fragments contribute to species richness in adjacent oil palm plantations[END_REF]). However, effects on functionally important groups were not always apparent. [START_REF] Gray | Are riparian forest reserves sources of invertebrate biodiversity spillover and associated ecosystem functions in oil palm landscapes?[END_REF] found a limited role of such natural habitats as sources of ants and dung beetles in tropical oil palm plantations, and [START_REF] Lucey | Spillover of insects from rain forest into adjacent oil palm plantations[END_REF] failed to show spillover effects from fragments into such plantations for ants.

Plateau fragments showed a lower richness of ant species when compared to river valley fragments. The latter fragment type may have provided more resources for ant species, such as shelter and food availability [START_REF] Tews | Animal species diversity driven by habitat heterogeneity/diversity: The importance of keystone structures[END_REF][START_REF] Stein | Environmental heterogeneity as a universal driver of species richness across taxa, biomes and spatial scales[END_REF]. River valley fragments keep a relatively high humidity even during the dry season with increases productivity whereas drought limits plant growth and thus resource availability in plateau fragments. Species composition of plateau fragments was a subset of river valley fragments confirming that a limited number of ecological niches was available in plateau fragments.

Our study demonstrated that remnant forest fragments are important habitats of predatory and omnivorous ant species that are involved in the regulation of sugarcane crop herbivores [START_REF] Choate | Ants as biological control agents in agricultural cropping systems[END_REF][START_REF] Lucey | Tropical forest fragments contribute to species richness in adjacent oil palm plantations[END_REF][START_REF] Offenberg | Review: Ants as tools in sustainable agriculture[END_REF]. The similarity in species composition between these natural habitats and sugarcane fields confirmed the potential refuge function of forest fragments. Although not visible in ␤ diversity comparisons between sampling dates, multivariate analysis based on ant frequencies confirmed a colonization of crop fields from forest fragments, since habitat differences in community composition after harvest disappeared later on in in the growing season. These findings were similar in sugarcane fields close to river valley and plateau fragments as the major forest remnants of the study region.

Fig. 1 .

 1 Fig. 1. Position of study sites (transects) and forest fragments in a sugarcane-dominated agricultural landscape in Brazil.

Fig. 2 .

 2 Fig. 2. Ant species richness along transects from inside forest fragments (left) into sugarcane fields (right) for two different sampling dates and fragment types: (A): one month after harvest, river valley; (B): one month after harvest, plateau; (C): four months after harvest, river valley; (D): four months after harvest, plateau. Regression lines are provided for significant relationships. Mean values ± SE.

Fig. 3 .

 3 Fig. 3. Ant frequency along transects from inside forest fragments (left) into sugarcane fields (right) for two different sampling dates and fragment types. Ant frequency is the number of occupied bait traps per distance averaged over all species and all sites within date and fragment type. (A) One month after harvest, river valley; (B) one month after harvest, plateau; (C) four months after harvest, river valley; (D) four months after harvest, plateau. Regression lines are provided for significant relationships. Mean values ± SE.

Fig. 4 .

 4 Fig. 4. Detrended correspondence analysis (DCA) on predatory ant communities one month (A, dry season) and four months (B, rainy season) after sugarcane harvest. Polygons indicate the position of the outmost samples within distance classes: forest fragments, field paths between fragment and sugarcane fields (three distances). The first two axes explained 29% of total variation in (A) and 22% in (B).

Table 1 .

 1 Results of mixed model ANOVA on ant species richness, frequency (total and dominant species) and relative ␤ diversity adjusted for ␥ diversity.

	Effect	DF Total richness	Total frequency	Relative ␤ diversity	Dorymyrmex brunneus	Pheidole oxyops
			F	P	F	P	F	P	F	P	F	P
	Fragment type	1	6.19 0.0229 0.14	0.7098 0.12	0.7358 0.46	0.5080 0.97	0.3382
	Distance	4	3.09 0.0174 2.02	0.0935	-		-4.32	0.0024 4.94	0.0009
	Distance × fragment	4	0.47 0.7574 0.52	0.7232	-		-1.02	0.4006 1.44	0.2239
	Date	1	16.63 <0.0001 11.06	0.0011 0.16	0.6880 22.74	<0.0001 0.10	0.7517
	Date × fragment	1	0.23 0.6345 0.69	0.4081 1.23	0.2740 1.41	0.2367 0.16	0.6878
	Distance × date	4	1.07 0.3737 1.25	0.2900	-		-1.60	0.1763 0.91	0.4597
	Distance × date × fragment 4	2.49 0.0450	125	0.2936	-		-1.09	0.3634 0.37	0.8317
	samples taken in October 2014 (dry season, one month after
	harvest) contained 25 species of ants whereas those taken in
	January 2015 (rainy season, four months after harvest) con-
	tained 33 species. Eighteen species were found at both dates,
	seven and 15 species were specific to the October and January
	sampling dates, respectively. The most diverse genera was
	Pheidole, with 18 species (45.0% of the total), followed by

Camponotus with six species (15%). Five species were common to all sites: Crematogaster quadriformis Roger, 1983, Dorymyrmex brunneus Forel, 1908, Pheidole oxyops Forel, 1908, Pheidole radoskowskii Mayr, 1884 and Pseudomyrmex termitarius Smith, 1855 (Appendix Table

L.A.O. Santos et al. / Basic and Applied Ecology xxx (2017) xxx-xxx

Please cite this article in press as: Santos, L. A. O., et al. The effect of forest fragments on abundance, diversity and species composition of predatory ants in sugarcane fields. Basic and Applied Ecology (2017), https://doi.org/10.1016/j.baae.2018.08.009

Available online at www.sciencedirect.comScienceDirect

Acknowledgements

The authors are grateful to Debora Rodrigues de Souza Campana and Otávio Guilherme Morais da Silva, UMC, Mogi das Cruzes, Brazil, who kindly identified the ants. Scholarship was provided to the first author by CAPES (Coordenac ¸ão de Aperfeic ¸oamento de Pessoal de Nível Superior).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in the online version, at https://doi.org/ 10.1016/j.baae.2018.08.009.