Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Spiders in wheat elds and semi-desert in the Negev (Israel)

Volume: 36Start Page: 368End Page: 37

Non-crop habitats in the landscape enhance spider diversity in wheat fields of a desert agroecosystem

Spiders (Araneae) are an important group of generalist predators in arable land. In temperate climates, spiders recolonise cropland annually from the surrounding landscape. In arid climates however, irrigated crops and the surrounding landscape matrix offer sharply different habitat conditions and this might negatively affect spider migration into crops. We studied whether the spider fauna in desert crops is influenced by the surrounding landscape in a similar way to that found in temperate climates. Spiders were sampled with pitfall traps in 13 wheat fields (Triticum aestivum L.) in the Negev Desert (Israel). The fields were situated along a gradient from crop- to non-crop-dominated landscapes (1–72% non-crop habitats). Species richness of spiders in wheat fields increased with the percentage of non-crop habitats in the landscape. In addition, activity-densities of crab spiders (Thomisidae) and cobweb spiders (Theridiidae) were enhanced by high percentages of non-crop habitats in the surrounding landscape. Activity-densities of the dominant sheetweb spiders (Linyphiidae) showed no significant response to landscape composition. As the immigrant spider families employ different foraging strategies than the dominant sheetweb spiders, they functionally enriched the spider fauna in crops and potentially increase the range of prey types consumed by spiders. Thus, non-crop habitats can be expected to increase the potential for biological control by spiders in nearby crops

Data from: Various competitive interactions explain niche separation in crop-dwelling web spiders

Competition for resources is a major organizing principle in communities of organisms that share similar ecological niches. Niche separation by means of exploitation or interference competition was investigated in two taxa of crop-inhabiting spiders that overlap in microhabitat use and have similar web design. Competition for prey and web sites was tested in microcosm experiments with the most common species that build sheet-webs: Enoplognatha gemina (Theridiidae) and Alioranus pastoralis (Linyphiidae). A field survey over the crop season provided data on spatial and temporal dispersion of Enoplognatha spp. (Theridiidae) and linyphiid spiders (Linyphiidae) and on availability of prey over the season. In the microcosm experiments, both taxa took springtails as prey, but only Enoplognatha fed on aphids. Differences in diet, however, could not be attributed to either exploitative or interference competition. Spatial separation of websites was attained by vertical displacement of webs in the vegetation (Enoplognatha) and by avoidance of patches occupied by conspecific or heterospecific individuals (linyphiids). In the field, densities of linyphiids and Enoplognatha were correlated negatively and webs were over-dispersed relative to a random distribution. Both taxa colonized the field at the start of the season; linyphiids colonized as adults, quickly reproduced, and had a second adult peak; Enoplognatha matured in the middle of the season and their numbers remained fairly constant over the season. The combined experimental manipulations and field data suggest that niche separation occurs at different scales. The hypothesis of competition for websites was partially supported, while prey preference (or tolerance) and temporal differences in life history stages also may explain the negative correlations between densities of the two taxa

Collections of spiders and prey from wheat fields (Israel)

Web building spiders (Linyphiidae and Theridiidae) were collected in 1X1m plots. Potential prey was collected using sticky traps located horizontally above groun

Predation of springtails and aphids by spiders

Results of microcosm experiment that tested the predation of Collembola and aphids by spiders (Lhinyphiidae and Theridiidae)

Effects of non-native Eucalyptus plantations on epigeal spider communities in the northern Negev desert, Israel

Volume: 43Start Page: 101End Page: 10

Modeling trophic dependencies and exchanges among insects’ bacterial symbionts in a host-simulated environment

Abstract Background Individual organisms are linked to their communities and ecosystems via metabolic activities. Metabolic exchanges and co-dependencies have long been suggested to have a pivotal role in determining community structure. In phloem-feeding insects such metabolic interactions with bacteria enable complementation of their deprived nutrition. The phloem-feeding whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) harbors an obligatory symbiotic bacterium, as well as varying combinations of facultative symbionts. This well-defined bacterial community in B. tabaci serves here as a case study for a comprehensive and systematic survey of metabolic interactions within the bacterial community and their associations with documented occurrences of bacterial combinations. We first reconstructed the metabolic networks of five common B. tabaci symbionts genera (Portiera, Rickettsia, Hamiltonella, Cardinium and Wolbachia), and then used network analysis approaches to predict: (1) species-specific metabolic capacities in a simulated bacteriocyte-like environment; (2) metabolic capacities of the corresponding species’ combinations, and (3) dependencies of each species on different media components. Results The predictions for metabolic capacities of the symbionts in the host environment were in general agreement with previously reported genome analyses, each focused on the single-species level. The analysis suggests several previously un-reported routes for complementary interactions and estimated the dependency of each symbiont in specific host metabolites. No clear association was detected between metabolic co-dependencies and co-occurrence patterns. Conclusions The analysis generated predictions for testable hypotheses of metabolic exchanges and co-dependencies in bacterial communities and by crossing them with co-occurrence profiles, contextualized interaction patterns into a wider ecological perspective