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1. Pollinators are declining globally, with climate change implicated as an important driver. Climate change can induce phenological shifts and reduce floral resources for pollinators, but little is known about its effects on floral attractiveness and how this might cascade to affect pollinators, pollination functions and plant fitness. 2. We used an in situ long-term drought experiment to investigate multiple impacts of reduced precipitation in a natural Mediterranean shrubland, a habitat where climate change is predicted to increase the frequency and intensity of droughts. Focusing on three insect-pollinated plant species that provide abundant rewards and support a diversity of pollinators (Cistus albidus, Salvia rosmarinus and Thymus vulgaris), we investigated the effects of drought on a suite of floral traits including nectar production and floral scent. We also measured the impact of reduced rainfall on pollinator visits, fruit set and germination in S. rosmarinus and C. albidus. 3. Drought altered floral emissions of all three plant species qualitatively, and reduced nectar production in T. vulgaris only. Apis mellifera and Bombus gr. terrestris visited more flowers in control plots than drought plots, while small wild bees visited more flowers in drought plots than control plots. Pollinator species richness did not differ significantly between treatments. Fruit set and seed set in S. rosmarinus and C. albidus did not differ significantly between control and drought plots, but seeds from drought plots had slower germination for S. rosmarinus and marginally lower germination success in C. albidus. 4. Synthesis. Overall, we found limited but consistent impacts of a moderate experimental drought on floral phenotype, plant reproduction and pollinator visits. Increased aridity under climate change is predicted to be stronger than the level assessed in the present study. Drought impacts will likely be stronger and this could profoundly affect the structure and functioning of plant–pollinator networks in Mediterranean ecosystems.

Sustainable soil management is essential to prevent agricultural soil degradation and maintain food production and core soil-based ecosystem services. Regenerative agriculture, one approach to sustainable soil management, is rapidly gaining traction in UK farming and policy. However, it is unclear what farmers themselves consider to be sustainable soil management practices, and how these relate to the principles of regenerative agriculture. Further, there is little insight into how sustainable soil management is currently promoted in agricultural knowledge and innovation services (AKIS). To address these knowledge gaps, we undertook the first national-scale survey of sustainable soil management practices in the UK, and complimented it with targeted interviews. We found high levels of awareness (>60%) and uptake (>30%) of most sustainable soil management practices among mixed and arable farmers. Importantly, 92% of respondents considered themselves to be practising sustainable soil management. However, our analysis shows that farmers combine practices in different ways. Not all these combinations correspond to the full set of regenerative agriculture principles of reduced soil disturbance, soil cover and crop diversity. To better understand the relationship between existing sustainable soil management practices in the UK and regenerative agriculture principles, we derive a ‘regenerative agriculture score’ by allocating individual practices among the principles of regenerative agriculture. Farmers who self-report that they are managing soil sustainably tend to score more highly across all five principles. We further find that sustainable soil management messaging is fragmented, and that few AKIS networks have sustainable soil management as their primary concern. Overall, our study finds that there are multiple understandings of sustainable soil management amongst UK farmers and land managers, and that they do not correspond to regenerative agriculture principles in a straight-forward way. This diversity and variety in sustainable soil management needs to be taken into account in future policy and research.

Omnivorous insects make foraging decisions between plant and prey resources depending on their accessibility, availability, and nutritional value. This shapes the stability and complexity of foodwebs, but also pest control services in agroecosystems. The mirid bug Lygus pratensis is a common cotton pest in China, but it also feeds on a variety of prey species. However, little is known about how different types of available resources affect its fitness and foraging behaviour. In laboratory experiments, we measured the fitness (survival, longevity and fecundity) of L. pratensis fed with bean pod only, bean + Aphis gossypii nymphs, or bean + Helicoverpa armigera eggs, and we also conducted focal observations of its foraging behaviour when provided the latter two. Adding H. armigera to its diet increased its fitness (both survival and fecundity), while adding A. gossypii was marginally detrimental. The different diets did not affect the time spent walking (searching for food resources) or preying, but significantly affected the time spent sapping bean tissue depending on L. pratensis life stage. Nymphs spent more time sapping plant when provided with H. armigera than A. gossypii (possibly through higher efficiency of handling prey). In addition, adults spent less time sapping plant than did nymphs (possibly through good efficiency of handling A. gossypii mobile prey and due to higher protein requirements). This special case of life-history omnivory highlights the complexity of natural foodwebs, where a major pest at the juvenile stage may reduce pest damage by preying on other pests species at the adult stage.

Fruit flies (Diptera: Tephritidae) are major pests of fruits and vegetables worldwide. We measured the efficacy of attractive lure mixtures in baited traps on naturally-occurring fruit flies in commercial mosaic guava and vegetables fields in Pakistan. We tested three mixtures (methyl-eugenol [ME] and cue lure [CL]; GF-120 and methyl eugenol; and GF-120 and cue lure) in eleven ratios: 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:0. We recorded three fruit fly species: Bactrocera zonata was the most abundant in baited traps, followed by Bactrocera dorsalis, while Zeugodacus cucurbitae was significantly less attracted to baited traps. We also found that the most attractive mixture and ratio varied among species: B. dorsalis was most attracted by 40CL:60ME, while B. zonata was most and equally attracted by 100ME, 10CL:90ME, 20CL:80ME, 30CL:70ME, and 40CL:60ME. Finally, Z. cucurbitae was most attracted by 10CL:90ME, which resulted in the highest total number of flies counted in 10CL:90ME-baited traps. Mixtures with GF-120 were less attractive to all three species. Our results suggest that lure mixtures in baited traps influence the attraction of fruit flies in a species-specific way. This needs to be considered in the integrated pest management of multiple species of fruit flies simultaneously. If Bactrocera species are most damaging and abundant, a 40CL:60ME mixture in baited traps will likely be most effective to reduce pest abundance and crop damage. However, if Z. cucurbitae is the main pest target causing most crop damage and yield loss, 10CL:90ME-baited traps will be a more effective in their monitoring and management.

Irradiation can be used as an insect pest management technique to reduce post-harvest yield losses. It causes major physiological changes, impairing insect development and leading to mortality. This technique is used to control the melon fly Zeugodacus cucurbitae, a major pest of Cucurbitaceae in Asia. Here, we applied irradiation to melon fly eggs, and the larvae emerged from irradiated eggs were used to conduct comparative transcriptomics and thereby identify key genes involved in the development and survival. We found 561 upregulated and 532 downregulated genes in irradiated flies compared to non-irradiated flies. We also observed abnormal small-body phenotypes in irradiated flies. By screening the 532 downregulated genes, we selected eight candidate genes putatively involved in development based in described functions in public databases and in the literature. We first established the expression profile of each candidate gene. Using RNA interference (RNAi), we individually knocked down each gene in third instar larvae and measured the effects on development. The knockdown of ImpE2 ecdysone-inducible gene controlling life stage transitions–led to major body size reductions in both pupae and adults. The knockdown of the tyrosine-protein kinase-like tok (Tpk-tok) caused severe body damage to larvae, characterized by swollen and black body parts. Adults subject to knockdown of the eclosion hormone (Eh_1) failed to shed their old cuticle which remained attached to their bodies. However, no obvious developmental defects were observed following the knockdown of the heat shock protein 67B1-like (Hsp67), the insulin receptor (Insr), the serine/threonine-protein kinase Nek4 (Nek4), the tyrosine-protein kinase transmembrane receptor Ror (Ror_1) and the probable insulin-like peptide 1 (Insp_1). We argue that irradiation can be successfully used not only as a pest management technique but also for the screening of essential developmental genes in insects via comparative transcriptomics. Our results demonstrate that ImpE2 and Eh_1 are essential for the development of melon fly and could therefore be promising candidates for the development of RNAi-based pest control strategies.

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), has invaded most Afro-Eurasian countries and is threatening worldwide tomato production. Various strategies have been developed and implemented to manage this pest. Here, we present a timely review on the up-to-date development and practical implementation of integrated pest management (IPM) programs for tomato crops across different world regions infested by T. absoluta. While insecticide resistance is a growing concern, biological control via releasing or conserving arthropod natural enemies and sex pheromone-based biotechnical control are the most successful management practices. Agronomic control-related research is an emerging area where the soil fertilization and/or irrigation, as well as breeding of resistant cultivars, has the potential to enhance IPM effectiveness. Grower survey responses in the native areas (i.e., South America), early-invaded areas (i.e., first report between 2006 and 2012) and newly invaded areas (i.e., first report after 2012) showed that the control programs evolved along with the areas and time since invasion. Growers in the early-invaded areas shifted more rapidly from chemical control to biological control compared to those from the native area. In all concerned regions, the pest control failure risk following chemical insecticide applications and the high cost associated with either biological or biotechnical control methods have been the greatest concerns for growers. The information gathered from the native and/or early-invaded areas may help achieve a more effective management in newly invaded areas. Lastly, researchers are expected to break the bottlenecks of some key issues that would enable lowering application cost of novel biorational alternative management options.

A thorough understanding of adaptation and speciation requires model organisms with both a history of ecological and phenotypic study as well as a robust set of genomic resources. For decades, the cactophilicDrosophilaspecies of the southwestern US and northern Mexico have fit this profile, serving as a crucial model system for understanding ecological adaptation, particularly in xeric environments, as well as the evolution of reproductive incompatibilities and speciation. Here, we take a major step towards gaining a complete molecular description of this system by assembling and annotating seven chromosome-lengthde novogenomes across the three speciesD. mojavensis, D. arizonae, andD. navojoa. Using this data, we present the most accurate reconstruction of the phylogenetic history of this clade to date. We further demonstrate a relationship between structural evolution and coding evolution both within and between species in this clade, and use this relationship to generate novel hypotheses for adaptation genes. All of our data are presented in a new public database (cactusflybase.arizona.edu), providing one of the most in-depth resources for the analysis of inter- and intraspecific evolutionary genomic data.

Banker plants increase biological pest control by supporting populations of non-pest arthropod species, used as alternative hosts or prey by natural enemies. Due to the specificity of trophic interactions, banker plants may not efficiently promote natural enemies with different ecologies. Yet in most cropping systems, different pest species are present together and require different biocontrol agents to efficiently control them. In the present study, we tested the combined use of two banker plants and their associated prey/host to enhance populations of the specialist parasitoid Encarsia formosa targeting the main tomato pest Bemisia tabaci, and a polyphagous ladybird Propylea japonica targeting the secondary pest Myzus persicae in tomato crops. In a laboratory and a greenhouse experiment, we measured the abundances of these four species using the Ricinus communis—Trialeurodes ricini banker plant system alone, in combination with the Glycines max—Megoura japonica system, or in absence of banker plants. We found that the first banker plant system enhanced populations of E. formosa, resulting in increased suppression of B. tabaci populations and the suppression of their outbreak in both our laboratory and greenhouse experiment. Conversely, abundances of P. japonica were not affected by this first system, but were significantly increased when the second was present. This resulted in increased control of M. persicae populations and the suppression of their early and late outbreaks. Our study demonstrates the potential for combined banker plants to provide long-term, sustainable control of multiple pests by their target natural enemies in complex agroecosystems.

In the context of global pollinator decline, little is known about the protection status and ecology of many species. This lack of knowledge is particularly important for Mediterranean protected areas that harbor diverse pollinator communities and are subject to considerable anthropogenic pressures. Calanques National Park (85 km2), which is located near Marseille (France), is dominated by Mediterranean low-vegetation habitats, such as phrygana and scrublands. These habitats offer favorable conditions for pollinator species due to the important amount of floral resources. Within a 10-yr period, we recorded bee (Hymenoptera: Apoidea: Anthophila), hover fly (Diptera: Syrphidae), and bee fly (Diptera: Bombyliidae) species and their interactions with the local flora through 10 field campaigns. We caught 250 pollinator species, including 192 bees, 38 hover flies, and 20 bee flies, for a total of 2,770 specimens. We recorded seven threatened bees (six near threatened and one endangered). Among the bee species, 47.9% were below-ground nesting species, and 54.7% were generalist species. Analysis of the pollination network showed that generalist and specialist pollinators do not share the same floral resources. The Cistaceae plant family (Malvales: Cistaceae) acted as a central node in the plant–pollinator network, interacting with 52 different pollinator species, which shows the importance of large open flowers that could be easily visited by both short and long-tongued pollinators in Mediterranean habitats. The occurrence of pollinator species and their ecological traits should strongly contribute to reinforcing the available information to provide or ameliorate the conservation statuses determined by IUCN Red List.

International audience; Flower strips can play an important role in agro-ecosystems by supporting populations of pests' natural enemies, thereby enhancing biological control. However, few studies have considered enhancing habitat for natural enemies around greenhouses. We conducted a two-year field experiment to (i) identify potential flowering species enhancing natural enemy populations but not pest populations; and (ii) evaluate how the presence of flower strips adjacent to greenhouses helped reduce pest abundance and insecticide use by attracting natural enemies inside greenhouses. We tested six flowering species in monofloral plots placed in flower strips adjacent to greenhouses and measured pest and predator abundance in monofloral plots but also on eggplants as well as eggplant yield and insecticide use inside greenhouses. All flowering species attracted more pests and predators than strips of naturally occurring weeds.Cosmos bipinnatusandBorago officinalishosted high predator abundance and low pest abundance. Conversely,Tagetes erectaandVerbena x hybridahosted intermediate predator abundance but high pest abundance, andCirsium setosumandCentaurea cyanushosted lower predator and pest abundances. Overall, both predator and pest numbers were higher at high flower density. Pest abundance was reduced by 43% in greenhouses adjacent to flower strips compared with control greenhouses, while predator numbers were 20 times higher, and insecticide use was reduced by 34%, but yields remained unchanged. Flower strips around greenhouses are therefore a promising, economically viable strategy to enhance pest control and to reduce insecticide use, and mixtures of flowering species in flower strips should be further tested to enhance the diversity of the predator community.

Banker plants increase biological pest control by supporting populations of non-pest arthropod species used as alternative hosts or prey by natural enemies. Due to the specificity of trophic interactions, banker plants may not efficiently promote natural enemies with different ecologies. Yet in most cropping systems different pest species are present together and require different biocontrol agents to efficiently control them. In the present study, we tested the combined use of two banker plants and their associated prey / host to enhance populations of the specialist parasitoid Encarsia formosa targeting the main tomato pest Bemisia tabaci, and a polyphagous ladybird Propylea japonica targeting the secondary pest Myzus persicae in tomato crops. In a laboratory and a greenhouse experiment, we measured the abundances of these four species using the Ricinus communis – Trialeurodes ricini banker plant system alone, in combination with the Glycines max – Megoura japonica system, or in absence of banker plants. We found that the first banker plant system enhanced populations of E. formosa, resulting in higher control of B. tabaci populations and the suppression of their outbreak in both our laboratory and greenhouse experiment. Conversely, abundances of P. japonica were not affected by this first system, but were significantly increased when the second was present. This resulted in high control of M. persicae populations and the suppression of their early and late outbreaks. Our study demonstrates the potential for combined banker plants to provide long-term, sustainable control of multiple pests by their target natural enemies in complex agroecosystems.

Parasitoids are a significant mortality factor in the population dynamics of many arthropods involved in key ecological processes such as herbivore-plant and predator-prey interactions. Parasitoids are therefore widely used in biocontrol programs. Global change phenomena influence these natural and anthropocentric roles of parasitoids and here we review the effects of the main drivers and their interplay. Land use intensification modifies landscape structure and elevates agroecosystem loads of fertilisers and pesticides creating risks for parasitism and loss of biocontrol services. Climate change can affect parasitoids directly, affecting physiology and survival, or indirectly via phenological and other effects (plant chemistry, herbivore-induced plant volatiles HIPVs) on their hosts, endosymbionts and plants. Biological invasions have the potential to modify native host-parasitoid systems and elevate risk of novel pest dynamics, requiring restoration of biocontrol. The interplay between these global change drivers may thus exacerbate the overall risk to parasitism in future agricultural landscapes. To make more accurate predictions, future studies could focus on the impact of interacting global change drivers on parasitoids and the biocontrol services they provide. Moreover, host and parasitoid specificity appear to be a key driver in assessing the effects of global change on parasitoids.

The Asian corn borer, Ostrinia furnacalis , is one of the most important pests of corn crops in Northern China. From 2004 to 2015, a public financial support to biological control of the corn borer resulted in a significant increase in the cultivated area treated with Trichogramma dendrolimi parasitoid applications in corn field in the Jilin Province, in northeastern China. In the present study, we analyzed the impact of these parasitoid releases, from 2000 to 2015 in the Jilin province, on the control of the corn borer as well as on pesticide use. We demonstrated that the widespread large-scale use of T. dendrolimi applications against the Asian corn borer, while being effective for controlling the pest and ensuring competitive corn yields, led to a decrease in insecticide use across the province. The use of Trichogramma is an economically and competitive alternative to insecticide applications in northeastern China.

In agroecosystems, predatory ladybeetles play an important role in restraining aphid population growth and suppressing aphid populations. They can adapt to various habitats and make use of various aphid species associated with multiple host plants during their life cycle. Agricultural landscapes in China are composed of a mosaic of small fields with a diverse range of crops, and how ladybeetles make use of host plant diversity in such landscapes has rarely been documented. In this study, we examined the relationship between aphid densities and ladybeetle densities in two different settings: (i) on the majority of plant species (including crops, trees, and weeds) at a local field scale in 2013 and 2014, and (ii) in paired cotton and maize crop fields at a regional landscape scale in 2013. Overall, we found that aphid abundance determined predatory ladybeetle abundance at both the local field and landscape scales, and there was a positive correlation between aphid densities and ladybeetle densities. However, plant taxa had no significant influence on the predatory ladybeetle abundance at the local field scale. In addition, the effect of aphids on ladybeetles abundance was influenced by the crop type and growing season at the regional landscape scale. There was a significant positive correlation between aphids and ladybeetles populations on cotton only in July and August, whereas the correlation was significant for maize throughout the whole growing season. We also conducted an analysis of the stable carbon isotope ratios of the adult ladybeetles caught in cotton and maize fields (C3 and C4 crops, respectively) in a regional landscape-scale survey in 2013. The &delta, 13Cvalue indicated that most prey aphids for ladybeetles originated from crops where aphids are abundant (cotton in June and July, both maize and cotton in August).These findings improved our understanding of the migration and dispersal of ladybeetles among different habitats and plant species and provided insight into the promotion of the regional conservation and pest control of natural enemies in northern China.

The emergence of third generation sequencing (3GS; long‐reads) is making closer the goal of chromosome‐size fragments in de novo genome assemblies. This allows the exploration of new and broader questions on genome evolution for a number of non‐model organisms. However, long‐read technologies result in higher sequencing error rates and therefore impose an elevated cost of sufficient coverage to achieve high enough quality. In this context, hybrid assemblies, combining short‐reads and long‐reads provide an alternative efficient and cost‐effective approach to generate de novo, chromosome‐level genome assemblies. The array of available software programs for hybrid genome assembly, sequence correction and manipulation are constantly being expanded and improved. This makes it difficult for non‐experts to find efficient, fast and tractable computational solutions for genome assembly, especially in the case of non‐model organisms lacking a reference genome or one from a closely related species. In this study, we review and test the most recent pipelines for hybrid assemblies, comparing the model organism Drosophila melanogaster to a non‐model cactophilic Drosophila, D. mojavensis. We show that it is possible to achieve excellent contiguity on this non‐model organism using the DBG2OLC pipeline.

The emergence of third generation sequencing (3GS; long-reads) is making closer the goal of chromosome-size fragments in de novo genome assemblies. This allows the exploration of new and broader questions on genome evolution for a number of non-model organisms. However, long-read technologies result in higher sequencing error rates and therefore impose an elevated cost of sufficient coverage to achieve high enough quality. In this context, hybrid assemblies, combining short-reads and long-reads provide an alternative efficient and cost-effective approach to generate de novo, chromosome-level genome assemblies. The array of available software programs for hybrid genome assembly, sequence correction and manipulation is constantly being expanded and improved. This makes it difficult for non-experts to find efficient, fast and tractable computational solutions for genome assembly, especially in the case of non-model organisms lacking a reference genome or one from a closely related species. In this study, we review and test the most recent pipelines for hybrid assemblies, comparing the model organism Drosophila melanogaster to a non-model cactophilic Drosophila, D. mojavensis. We show that it is possible to achieve excellent contiguity on this non-model organism using the DBG2OLC pipeline.

International audience

Agricultural landscapes are fast-changing systems due to crop planting and harvesting. These events strongly influence movements of arthropod pests and their natural enemies, yet they are insufficiently considered to implement informed pest management strategies. In China, the adoption of Bt-cotton crops at very large scales has given rise to the recent pest status of mirid bugs such as Apolygus lucorum in cotton fields. In this study we relied on carbon 13 stable isotope analysis to estimate the dispersal of A. lucorum in the Bt-cotton agricultural landscape, composed of a mosaic of cotton and maize and other minor crops. We showed that a diet on C3-plants including cotton induced a significantly different signature than the C4-plant maize. Based on δ13C ratios, we showed that more than 75% of mirid bugs caught in maize fields did not originate in situ, since they had a C3-diet and therefore most likely dispersed from neighbouring cotton fields. Conversely, less than 10% of mirid bugs in cotton fields had a diet on C4-plants, so the vast majority of them did not disperse from maize fields but instead likely stayed in cotton fields. We also observed a delayed establishment of A. lucorum populations in maize fields compared to cotton fields, likely due to host phenology. Indeed we showed in laboratory that juveniles’ survival rate and adults’ fecundity are high on maize silk and grain only, whose resources are available in the field shortly before harvest. Unidirectional movements of mirids from cotton to maize associated with poor developmental success on maize highlight the high potential of maize fields to act as a sink for A. lucorum mirid bug pests. This could be wisely implemented in IPM programs to enhance the management of mirid bug population outbreaks in cotton fields and reduce yield loss on cotton.

International audience; 1. Conservation biological control aims to control pests by promoting wild populations of natural enemies. One challenge is to attract and retain efficient natural enemies in crop fields, which often are a suboptimal environment. Towards this goal, the attract-and-reward strategy relies on combining attractive synthetically produced herbivore-induced plant volatiles (HIPVs) with companion plants (non-crop plants which provide alternative resources to the targeted natural enemies). Although severely overlooked, the spatial arrangement of HIPV dispensers and rewards inside crop fields may strongly influence the foraging behaviour and persistence of natural enemies and thus the success of this pest management strategy.2. We tested the impact of two contrasting spatial arrangements of HIPV dispensers and rewards, alternatively inside and around a block of target apple trees, on the efficacy of the biological control of Aphis citricola populations by the common predatory ladybird Propylea japonica in apple orchards in northern China. We used synthetic methyl salicylate (MeSA) as an attractant and the companion plant Calendula officinalis as a reward. To better understand how the spatial arrangement of MeSA dispensers and companion plants affected the attraction and foraging behaviour of adult ladybirds, we conducted indoor experiments in a flight mill, an olfactometer and a wind-tunnel.3. Blocks of target trees treated with MeSA dispensers inside and companion plants around provided the most efficient pest control in orchards, compared with the opposite spatial arrangement.4. The synthetic MeSA dispenser and the companion plant synergistically attracted ladybirds in the olfactometer and enhanced their flight activity in the flight mill. In the wind-tunnel, MeSA served as a spatial cue for ladybirds to find nearby prey, while companion plants were sought in the absence of prey.5. Synthesis and applications. The present study will help further improvements of aphid control in apple orchards through a careful spatial arrangement of herbivore-induced plant volatiles dispensers (HIPVs) and rewards (companion plants) in optimized attract-and-reward strategies. Without such assessment, these strategies may be hazardous even with well-identified targeted natural enemies. Associated lab experiments highlight that HIPVs and companion plants interactively influence ladybird foraging pattern, and that their spatial arrangement can modulate the ability of such key predators to find their prey. KEYWORDS attract-and-reward, foraging behaviour, integrated pest management, methyl salicylate, natural enemies, semiochemicals,synomone How to cite this article: Jaworski CC, Xiao D, Xu Q, et al. Varying the spatial arrangement of synthetic herbivore-induced plant volatiles and companion plants to improve conservation biological control. J Appl Ecol. 2019;00:1-13.

International audience; 1. Spatial processes have a major influence on the stability of species interaction networks and their resilience to environmental fluctuations. Here, we combine field observations and a dynamic model to understand how spatial processes may affect a network composed of the flowering plant Antir-rhinum majus, its cohort of pollinators, and a specialist seed-predator and its parasitoid.2. The interactions taking place within this system were investigated by determining the fate of flowers and fruits on flowering and fruiting stems at 16 study sites. We then used this information to estimate spatial and temporal variation in the pollination rate, parasitism rate and hyperparasitism rate.3. We found that the plants were pollinator-limited, with relatively variable fruit-to-flower ratios across sites. On almost all sites, plants were both parasitized and hyperparasitized, at a low to moderate rate.4. Comparing our field observations with a tritrophic Nicholson-Bailey model, we found that empirical data are not always consistent with the conditions for local tritrophic persistence. This suggests that other mechanisms such as random disturbances and recolonizations (patch dynamics) or inter-site migration through metacommunity dynamics (source-sink dynamics) play a role in this system. Model simulations showed that dispersal could contribute to increasing tritrophic persistence in this system, and that source-sink structure, not just environmental stochasticity, may cause the observed pattern of spatial variation.5. Synthesis. We defined and measured metrics related to species interactions and densities. This led us to suggest that the functioning of the A. majus metacommunity is more consistent with source-sink than patch metacommunity dynamics, highlighting the extent to which dispersal explains the persistence of the system.

Erratum : http://link.springer.com/article/10.1007/s10340-015-0705-8/fulltext.html (doi: 10.1007/s10340-015-0705-8); International audience; Increased pest control by generalist predators has been successfully achieved in several cases by promoting apparent competition, which is the reciprocal negative interactions between prey mediated by their shared predator. However, the presence of alternative prey does not always result in an improved control of the target pest species, due to the complexity and specificity of biotic interactions. To increase the effectiveness of IPM programs, a fine understanding of the interactions among co-occurring pest species and their biocontrol agents is necessary. We tested the occurrence of apparent competition between the major tomato pests Tuta absoluta and Bemisia tabaci when preyed on by a generalist mirid bug Macrolophus pygmaeus, by monitoring pest and predator population dynamics in a greenhouse experiment. We also measured the cascading effect of the shared predator on plant and fruit damage due to pests. We observed higher predator population growth and reduced population densities of both prey in treatments with two prey, as compared to treatments with one prey, showing that apparent competition occurred. Plant and fruit damage caused by B. tabaci was reduced in the presence of T. absoluta, but damage due to T. absoluta, which accounted for the major part, was not reduced in the presence of B. tabaci, resulting in similar levels of total damage when pests co-occurred. This study demonstrates that, even if promoting apparent competition leads to actual reduction in pest densities, yield loss may not be reduced when this strategy is applied to major pests such as T. absoluta.

Erratum de la notice de "Apparent competition between major pests reduces pest population densities on tomato crop, but not yield loss" http://prodinra.inra.fr/record/335895; International audience