Landscape composition influences patterns of native and exotic lady beetle abundance

Establishment and Expansion Scenario of Drosophila suzukii (Diptera: Drosophilidae) in Central Brazil

Drosophila suzukii Matsumura (Diptera: Drosophilidae), also known as spotted wing drosophila (SWD), is an important pest that damages various wild and cultivated soft fruits worldwide, especially in the Northern Hemisphere. In Brazil, it occurs mainly in the subtropical climates of the southern and southeastern regions. However, SWD has also been sporadically found in the central region of the country in the natural vegetation of the tropical Brazilian Savanna. In this study, we investigated the occurrence of SWD at the northern limit of its range in South America - the central region of Brazil - by monitoring an established drosophilid community in an orchard located in the Brazilian Federal District. We also investigated the current geographical distribution of this pest in Brazil and its potential geographical distribution using species distribution models under two different future shared socioeconomic pathways scenarios (2040 and 2060, optimist and pessimist). Twenty drosophilid species were detected among the 6,396 captured specimens, most of which are exotic in the Neotropical region. The fly community greatly fluctuated throughout the year, and the highest abundance of SWD (3.5% relative abundance and 1.38 flies/trap/day) was recorded in April during the rainy season. Potential distribution models indicate that suitable areas for SWD spread will decrease in the south and southeast but increase in the central region of Brazil. We recommend continuous SWD monitoring and improving bioclimatic forecast models for mitigating damage to local fruit production.

Avian regulation of crop and forest pests, a meta-analysis

BACKGROUND

Birds have been shown to reduce pest effects on various ecosystem types. This study aimed to synthesize the effect of birds on pest abundance, product damage and yield in agricultural and forest systems in different environments. Our hypothesis is that birds are effective pest regulators that contribute to a reduction in pest abundance, enhancement of yield quality and quantity and economic profit, and that pest regulation may depend on moderators such as the type of ecosystem, climate, pest, and indicator (ecological or economic).

RESULTS

We performed a systematic literature review of experimental and observational studies related to biological control in the presence and absence of regulatory birds. We retained 449 observations from 104 primary studies that were evaluated through qualitative and quantitative analyses. Of the 79 studies with known effects of birds on pest regulation, nearly half of the 334 observations showed positive effects (49%), 46% showed neutral effects, and very few (5%) showed negative effects. Overall effect sizes were positive (mean Hedges' d = 0.38 ± 0.06). A multiple model selection retained only ecosystem and indicator types as significant moderators.

CONCLUSION

Our results support our hypothesis that there is a positive effect of avian control of pests for each analyzed moderator and this effect was significant for both ecological and economic indicators. Avian regulation of pests is a potential effective approach for environmentally friendly pest management that can reduce pesticide use regardless of the context of implementation. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Promoting Beneficial Arthropods in Urban Agroecosystems: Focus on Flowers, Maybe Not Native Plants

(1) Urbanization threatens biodiversity, yet urban native plants support native biodiversity, contributing to conservation and ecosystem services. Within urban agroecosystems, where non-native plants are abundant, native plants may boost the abundance and richness of beneficial arthropods. Nevertheless, current information focuses on pollinators, with little attention being paid to other beneficials, like natural enemies. (2) We examined how the species richness of native plants, garden management, and landscape composition influence the abundance and species richness of all, native, and non-native bees, ladybeetles, ants, and ground-foraging spiders in urban agroecosystems (i.e., urban community gardens) in California. (3) We found that native plants (~10% of species, but only ~2.5% of plant cover) had little influence on arthropods, with negative effects only on non-native spider richness, likely due to the low plant cover provided by native plants. Garden size boosted native and non-native bee abundance and richness and non-native spider richness; floral abundance boosted non-native spider abundance and native and non-native spider richness; and mulch cover and tree and shrub abundance boosted non-native spider richness. Natural habitat cover promoted non-native bee and native ant abundance, but fewer native ladybeetle species were observed. (4) While native plant richness may not strongly influence the abundance and richness of beneficial arthropods, other garden management features could be manipulated to promote the conservation of native organisms or ecosystem services provided by native and non-native organisms within urban agroecosystems.

A roadmap for ladybird conservation and recovery

Ladybirds (Coleoptera: Coccinellidae) provide services that are critical to food production, and they fulfill an ecological role as a food source for predators. The richness, abundance, and distribution of ladybirds, however, are compromised by many anthropogenic threats. Meanwhile, a lack of knowledge of the conservation status of most species and the factors driving their population dynamics hinders the development and implementation of conservation strategies for ladybirds. We conducted a review of the literature on the ecology, diversity, and conservation of ladybirds to identify their key ecological threats. Ladybird populations are most affected by climate factors, landscape composition, and biological invasions. We suggest mitigating actions for ladybird conservation and recovery. Short-term actions include citizen science programs and education, protective measures for habitat recovery and threatened species, prevention of the introduction of non-native species, and the maintenance and restoration of natural areas and landscape heterogeneity. Mid-term actions involve the analysis of data from monitoring programs and insect collections to disentangle the effect of different threats to ladybird populations, understand habitat use by taxa on which there is limited knowledge, and quantify temporal trends of abundance, diversity, and biomass along a management-intensity gradient. Long-term actions include the development of a worldwide monitoring program based on standardized sampling to fill data gaps, increase explanatory power, streamline analyses, and facilitate global collaborations.

Ladybird communities in rural woodlands: Does an invader dominate?

The invasive alien species Harmonia axyridis (Coleoptera: Coccinellidae) was first observed in the UK in 2004. Previous studies have demonstrated the adverse effects on other species of H. axyridis during its early stages of establishment. However, habitat factors are important in determining distribution and population trends of ladybirds. Whilst the abundance of H. axyridis is well known in the UK within urban and other managed habitats, much less is known about its abundance in the wider countryside. Here we present the results of surveys from rural woodland habitats to assess whether or not H. axyridis dominates coccinellid communities in these rural habitats. Additionally, we explored the relationship between coccinellid and aphid abundance within these habitats. All field sites were in Cambridgeshire or Suffolk, East Anglia, UK and were surveyed between May and October 2016 and 2017. Three deciduous sites and three coniferous sites were included in the study. Surveys were conducted using a standardised approach involving sweep-netting within grass margins and tree beating to sample ladybirds from trees. Three distinct vegetation structures or layers were surveyed within both the coniferous and deciduous sites; tree, shrub and herb layer. All captured coccinellids were identified to species-level. Seventeen species of coccinellid and over 1300 individuals were recorded during the study period from two distinct site types (deciduous, coniferous). Species richness was lower at deciduous sites (n = 12) in comparison to coniferous (n = 16) sites. The coccinellid community also did not appear to be dominated by H. axyridis at rural sites, in contrast to urban areas. Deciduous woodland appeared to be a lesser preferred habitat of H. axyridis than coniferous woodland. Additionally, there was a distinct difference in the coccinellid community in relation to vegetation structure (across the tree, shrub and herb layers) between coniferous and deciduous sites. Our results indicate that there appear to be distinct native coccinellid communities at deciduous and coniferous sites. We discuss the way in which rural woodlands could act as a refuge for some native coccinellids.

Declining Abundance of Coccinellidae (Coleoptera) Among Crop and Prairie Habitats of Eastern South Dakota, USA

Lady (= ladybird) beetles (Coleoptera: Coccinellidae) provide agroecosystem services as major predators of aphids and other pests of field crops. Several native coccinellids in North America have declined in association with the introduction of invasive species of lady beetles. In particular, populations of three native species declined drastically (Coccinella transversoguttata richardsoni) or effectively disappeared (Coccinella novemnotata, Adalia bipunctata) from agricultural landscapes in eastern South Dakota, U.S.A., following establishment of an invasive coccinellid (Coccinella septempunctata) in the 1980s. Since then, two other non-native coccinellids (Harmonia axyridis and Hippodamia variegata) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous coccinellid guild is lacking. This paper summarizes long-term results from 14 years (2007–2020) of sampling coccinellids by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,338 aphidophagous coccinellids comprising 10 species were sampled. Two invasive species (Coc. septempunctata, Har. axyridis) were the third- and fourth-most abundant species, respectively. The seven most abundant species constituted 99% of all coccinellids sampled and were recorded from all six habitats. However, coccinellid species ranged considerably in their evenness of habitat use, resulting in differences in rank abundance among habitats. Coccinellid assemblages were similar for alfalfa and winter wheat, but not for other habitats, which possessed distinct coccinellid assemblages based on rank abundance. Annual abundance of coccinellids varied considerably within habitats, but declining trends were evident from significant negative regressions in annual abundance for adult and immature coccinellids in corn and adults in soybean. As a group, native adult coccinellids showed a significant declining trend in corn but not in other habitats, whereas trends for non-native adult coccinellids were non-significant in all habitats. Sample rates of coccinellids in alfalfa, spring grains, and corn in this study were 74, 26, and 6%, respectively, compared to that of a previous study from the region, further indicating substantial decreases in coccinellid abundance. Possible explanations and implications for observed patterns in coccinellid diversity and individual species abundances in field crops and restored prairie of eastern South Dakota are discussed with respect to prey, agronomic trends, and landscape factors.

Does the non-native Harlequin ladybird disrupt the feeding behaviour of the native two-spot ladybird?

Since its arrival in 2004, the non-native Harlequin ladybird Harmonia axyridis (Coleoptera: Coccinellidae) has rapidly spread throughout Britain, and it is now the most common coccinellid in England. There have since been concerns about the detrimental effects it may have on native coccinellids because there is a strong correlation between the arrival of H. axyridis and the decline in native species, including the two-spot ladybird, Adalia bipunctata. However, there have been few studies of the behavioural interactions between these two species, which occupy a high-niche overlap. This study investigated if the presence of H. axyridis impacts the feeding behaviour of A. bipunctata through direct competition for aphid prey. Foraging and interactive behaviour of A. bipunctata and H. axyridis were investigated within microcosms. Adalia bipuncata exhibited a similar consumption rate and time in the presence of H. axridis, yet H. axyridis consumed 3.5 times more prey items and were seven times faster compared to A. bipuncata. Observations showed that H. axyridis does not directly disrupt the feeding behaviour of A. bipunctata, but rather indirectly excludes the native species through being a superior competitor for prey items. Results indicate that the decline in native coccinellid species may be a consequence of H. axyridis competitive advantage, but that the concept of coexistence should not be dismissed.

Community science data suggests that urbanization and forest habitat loss threaten aphidophagous native lady beetles

Community scientists have illustrated rapid declines of several aphidophagous lady beetle (Coccinellidae) species. These declines coincide with the establishment of alien coccinellids. We established the Buckeye Lady Beetle Blitz program to measure the seasonal occupancy of coccinellids within gardens across a wide range of landscape contexts. Following the Habitat Compression Hypothesis, we predicted that gardens within agricultural landscapes would be alien-dominated, whereas captures of natives would be higher within landscapes encompassing a high concentration of natural habitat.Within the state of Ohio, USA, community scientists collected lady beetles for a 7-day period across 4 years in June and August using yellow sticky card traps. All identifications were verified by professional scientists and beetles were classified by three traits: status (alien or native), mean body length, and primary diet. We compared the relative abundance and diversity of coccinellids seasonally and determined if the distribution of beetles by size, status, and diet was related to landscape features.Alien species dominated the aphidophagous fauna. Native aphidophagous coccinellid abundance was positively correlated with forest habitat while alien species were more common when gardens were embedded within agricultural landscapes. Urbanization was negatively associated with both aphidophagous alien and native coccinellids. Synthesis and Applications: Our census of native coccinellid species within residential gardens-a widespread and understudied habitat-was enabled by volunteers. These data will serve as an important baseline to track future changes within coccinellid communities within this region. We found that native coccinellid species richness and native aphidophagous coccinellid abundance in gardens were positively associated with forest habitat at a landscape scale of 2 km. However, our understanding of when and why (overwintering, summer foraging, or both) forest habitats are important remains unclear. Our findings highlight the need to understand how declining aphidophagous native species utilize forest habitats as a conservation priority.

Effects of Aphid Density and Plant Taxa on Predatory Ladybeetle Abundance at Field and Landscape Scales

Simple Summary

In agroecosystems, predatory ladybeetles play an important role in suppressing aphid populations. How ladybeetles make use of host plant diversity in multicropping landscapes has rarely been documented in China. In this study, we examined the relationship between aphid densities and ladybeetle densities at both the local field and landscape scales. Overall, we found that there was a positive correlation between aphid densities and ladybeetle densities. However, plant taxa had no significant influence on 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 aphid and ladybeetle populations on cotton only in July and August, whereas the correlation was significant for maize throughout the whole growing season. The δ¹³C value 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 regional conservation and pest control of natural enemies in Northern China.

Abstract

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 δ¹³Cvalue 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.

Landscape configuration and habitat complexity shape arthropod assemblage in urban parks

The urbanization process systematically leads to the loss of biodiversity. Only certain arthropods are resilient to the urbanization process and can thrive in the novel conditions of urbanized landscapes. However, the degree to which arthropod communities survive in urban habitats depends on landscape and local effects and biological interactions (e.g., trophic interactions). In the present study, we examined the relative importance of various factors at landscape (isolation, edge density and area of surrounding greenery) and local (size of park, canopy cover, understory vegetation cover, defoliation depth, weight of dried leaves, soil temperature, soil moisture, and soil pH) spatial scales on the diversity of ants, beetles and spiders in urban parks. Our results indicated that park edge density was negatively correlated with diversity metrics in ants, beetles, and spiders in urban parks relative to the degree of proximity with the peri-urban forest. In other words, parks that located adjacent to the peri-urban forest may not necessarily have high biodiversity. The results suggested that man-made structures have been effective dispersal barriers that limit the spillover effects of ants and spiders but not the spillover of comparatively strong fliers, such as beetles. However, the area of surrounding greenery may have facilitated the colonization of forest-dependent taxa in distant parks. Large parks with reduced edge density supported a higher arthropod diversity because of the minimal edge effect and increased habitat heterogeneity. Vegetation structure consistently explained the variability of ants, beetles, and spiders, indicating that understory plant litter is crucial for providing shelters and hibernation, oviposition, and foraging sites for the major taxa in urban parks. Therefore, efforts should focus on the local management of ground features to maximize the conservation of biological control in urban landscapes.

Thiamethoxam Differentially Impacts the Survival of the Generalist Predators, Orius insidiosus (Hemiptera: Anthocoridae) and Hippodamia convergens (Coleoptera: Coccinellidae), When Exposed via the Food Chain

Insect predators are seldom considered during toxicological trophic assessments for insecticide product development. As a result, the ecological impact of novel insecticides on predators is not well understood, especially via the food chain, i.e., when their prey is exposed to insecticides. Neonicotinoids are systemic insecticides widely used in agriculture to control herbivorous insects, but their effects on predatory insects via the food chain have not been well characterized. In this study, we documented the time-course effects of the neonicotinoid thiamethoxam on the survival of two predators, the insidiosus flower bug Orius insidiosus (Say) and the convergent lady beetle Hippodamia convergens Guérin-Méneville, when preying upon the aphids Aphis glycines Matsumura (Hemiptera: Aphididae), Aphis gossypii Glover (Hemiptera: Aphididae), and Myzus persicae (Sulzer) (Hemiptera: Aphididae). Aphids were exposed to thiamethoxam-treated or untreated plants every week over the course of 5 wk. After transferring aphids to Petri dishes, predators were allowed to feed on aphids. We found that the survival of the insidiosus flower bug, but not the convergent lady beetle, was reduced after consuming aphids reared on thiamethoxam-treated plants compared to untreated plants. Survival reduction of the insidiosus flower bug was observed only during the first weeks after thiamethoxam application; no reduction occurred 28 d after treatment or beyond. These results demonstrate that a systemic application of thiamethoxam could be compatible with convergent lady beetles and insidiosus flower bugs, if the time of predator release does not coincide with thiamethoxam activity. These findings are critical for the development of future pest control programs that integrate biological and chemical control.

Diversified Farming in a Monoculture Landscape: Effects on Honey Bee Health and Wild Bee Communities

In the last century, a global transformation of Earth's surface has occurred due to human activity with extensive agriculture replacing natural ecosystems. Concomitant declines in wild and managed bees are occurring, largely due to a lack of floral resources and inadequate nutrition, caused by conversion to monoculture-based farming. Diversified fruit and vegetable farms may provide an enhanced variety of resources through crops and weedy plants, which have potential to sustain human and bee nutrition. We hypothesized fruit and vegetable farms can enhance honey bee (Hymenoptera: Apidae, Apis mellifera Linnaeus) colony growth and nutritional state over a soybean monoculture, as well as support a more diverse wild bee community. We tracked honey bee colony growth, nutritional state, and wild bee abundance, richness, and diversity in both farm types. Honey bees kept at diversified farms had increased colony weight and preoverwintering nutritional state. Regardless of colony location, precipitous declines in colony weight occurred during autumn and thus colonies were not completely buffered from the stressors of living in a matrix dominated with monocultures. Contrary to our hypothesis, wild bee diversity was greater in soybean, specifically in August, a time when fields are in bloom. These differences were largely driven by four common bee species that performed well in soybean. Overall, these results suggest fruit and vegetable farms provide some benefits for honey bees; however, they do not benefit wild bee communities. Thus, incorporation of natural habitat, rather than diversified farming, in these landscapes, may be a better choice for wild bee conservation efforts.

Geostatistical Assessment of Frankliniella schultzei (Thysanoptera: Thripidae) Spatial Distribution in Commercial Watermelon Crops

Spatial distribution studies of insect pests make it possible to determine their colonization and dispersal patterns. Watermelon (Citrullus lanatus (Thunb.) Matsum. et Nakai) is among the most frequently consumed fruits in the world, and the common blossom thrips, Frankliniella schultzei (Trybom) (Thysanoptera: Thripidae), is one of the most important insect pests of this plant. The objective of this study was to determine the spatial distribution of F. schultzei in commercial watermelon crops using geostatistics. The studied F. schultzei populations presented an aggregated distribution. The colonization of thrips began at the borders of the crops, especially in the areas located in the opposite direction to that of the prevailing winds. The highest densities of thrips occurred in crops that had cucurbits in the surrounding areas. When monitoring for F. schultzei populations, greater attention should be given to sampling that part of the crop located in the opposite direction to that of the prevailing winds because this is where colonization begins. Even at low densities, the aggregation points of thrips in the crop should be located and controlled so that they do not cause damage. In sampling programs for F. schultzei, samples should be taken at distances greater than 9 m apart because this is the distance up to which densities of this species show spatial dependence. Planting watermelon crops close to other cucurbits should be avoided, as these alternate hosts may act as a source of infestation by this pest.

Native habitat mitigates feast-famine conditions faced by honey bees in an agricultural landscape

Intensive agriculture can contribute to pollinator decline, exemplified by alarmingly high annual losses of honey bee colonies in regions dominated by annual crops (e.g., midwestern United States). As more natural or seminatural landscapes are transformed into monocultures, there is growing concern over current and future impacts on pollinators. To forecast how landscape simplification can affect bees, we conducted a replicated, longitudinal assessment of honey bee colony growth and nutritional health in an intensively farmed region where much of the landscape is devoted to production of corn and soybeans. Surprisingly, colonies adjacent to soybean fields surrounded by more cultivated land grew more during midseason than those in areas of lower cultivation. Regardless of the landscape surrounding the colonies, all experienced a precipitous decline in colony weight beginning in August and ended the season with reduced fat stores in individual bees, both predictors of colony overwintering failure. Patterns of forage availability and colony nutritional state suggest that late-season declines were caused by food scarcity during a period of extremely limited forage. To test if habitat enhancements could ameliorate this response, we performed a separate experiment in which colonies provided access to native perennials (i.e., prairie) were rescued from both weight loss and reduced fat stores, suggesting the rapid decline observed in these agricultural landscapes is not inevitable. Overall, these results show that intensively farmed areas can provide a short-term feast that cannot sustain the long-term nutritional health of colonies; reintegration of biodiversity into such landscapes may provide relief from nutritional stress.

Environmental and spatial filtering of ladybird beetle community composition and functional traits in urban landscapes

Urban community gardens provide habitat for biodiversity within urban landscapes. Beneficial insects, those that provide important ecosystem services like pollination and pest control, are among the many inhabitants of these green spaces. Garden management and the composition of the urban matrix in which they are embedded can affect not only the abundance and species richness of beneficial insects but also their community composition and functional traits. During 2014 and 2015 (June to September), we collected ladybird beetles (Coleoptera: Coccinellidae) in 19 community gardens in three counties of the California Central Coast. We examined the effects of garden- and landscape-level characteristics on ladybird community composition and functional traits. Out of the 19 species collected, only 3 were non-native to California (3 were not identified to species). Similarities in ladybird species composition were not driven by geographic distance between gardens, which suggest that beetles in these landscapes are not experiencing dispersal limitation. Instead, three landscape-level environmental variables and seven garden-scale ones correlated with changes in community composition. Even though we perceive cities as highly disturbed low-quality landscapes, our results suggest that highly mobile arthropods such as ladybird beetles, may not perceive the urban matrix as a barrier to movement and that urban gardens can be inhabited by native species with different sizes, diet breadths and diets. Nevertheless, our results also suggest garden specific management practices, such as altering ground cover, can affect the taxonomic and functional composition of ladybird beetles with potential implications to their ecosystem services.

Local pesticide use intensity conditions landscape effects on biological pest control

Complex landscapes including semi-natural habitats are expected to favour natural enemies thereby enhancing natural pest biocontrol in crops. However, when considering a large number of situations, the response of natural biocontrol to landscape properties is globally inconsistent, a possible explanation being that local agricultural practices counteract landscape effects. In this study, along a crossed gradient of pesticide use intensity and landscape simplification, we analysed the interactive effects of landscape characteristics and local pesticide use intensity on natural biocontrol. During 3 years, using a set of sentinel prey (weed seeds, aphids and Lepidoptera eggs), biocontrol was estimated in 80 commercial fields located in four contrasted regions in France. For all types of prey excepted weed seeds, the predation rate was influenced by interactions between landscape characteristics and local pesticide use intensity. Proportion of meadow and length of interface between woods and crops had a positive effect on biocontrol of aphids where local pesticide use intensity was low but had a negative effect elsewhere. Moreover, the landscape proportion of suitable habitats for crop pests decreased the predation of sentinel prey, irrespectively of the local pesticide use intensity for weed seeds, but only in fields with low pesticide use for Lepidoptera eggs. These results show that high local pesticide use can counteract the positive expected effects of semi-natural habitats, but also that the necessary pesticide use reduction should be associated with semi-natural habitat enhancement to guarantee an effective natural biocontrol.

Mixed effects of landscape complexity and insecticide use on ladybeetle abundance in wheat fields

BACKGROUND

Although the abundance of insect natural enemies in crop fields may be influenced by the surrounding landscape and local field management, particularly insecticide use at the local scale, few studies have examined these factors simultaneously. In this study, we investigated the effects of landscape context and insecticide use in local fields on ladybeetle abundance in wheat fields in northern China.

RESULTS

Woodlots and fallow land were the most important landscape variables enhancing ladybeetle abundance. We used the cumulative percentage of these land types to characterize landscape complexity. Comparing the change in ladybeetle abundance in wheat fields within different landscapes and with different in-field insecticide regimes, we found that although more complex landscapes enhanced ladybeetle abundance, the negative effects of insecticide use on ladybeetle populations were not offset by landscape complexity. Additionally, the positive effects of more complex landscapes on ladybeetle abundance were not significant in wheat fields subjected to high insecticide use.

CONCLUSION

Ladybeetle abundance is enhanced by landscape complexity, but this is modified by insecticide use in local fields. Within-field efforts to maximize the conservation biological control of pests to improve crop yield should take into account the influence of the surrounding landscape. © 2018 Society of Chemical Industry.

Differences in the Phenology of Harmonia axyridis (Coleoptera: Coccinellidae) and Native Coccinellids in Central Europe

Harmonia axyridis (Pallas), an invasive non-native species in central Europe, can outcompete other aphidophagous species. The distribution and abundance of H. axyridis vary depending on different host plants, and its effects on native coccinellid communities may change accordingly. The distribution and abundance of coccinellids in central Europe (50°N, 14°E) were investigated from 2010 to 2016. Coccinellids were counted at regular intervals on cereals (Avena, Hordeum, and Triticum), herbaceous plants (Matricaria and Urtica) and trees (Acer, Betula, and Tilia). Additionally, the occurrence over time of each species on these plants was assessed and used as an index of persistence. Across all years, the adults and larvae of H. axyridis were the dominant species of coccinellid on trees. However, H. axyridis was less abundant on herbaceous plants and cereals than on trees. Populations of native coccinellids and H. axyridis co-occurred on trees and persisted for the same length of time, while native coccinellids persisted longer than H. axyridis on herbaceous plants and cereals. Compared to 1976-1986, in the 2010s, the abundance of native species decreased on all plants by 50-70%. The presence of H. axyridis could be considered as a factor driving changes in the assemblages of native coccinellids.

Demographic histories of three predatory lady beetles reveal complex patterns of diversity and population size change in the United States

Predatory lady beetles (Coccinellidae) contribute to biological control of agricultural pests, however, multiple species frequently compete for similar resources in the same environment. Numerous studies have examined ecological interactions among the native North American convergent lady beetle (Hippodamia convergens) and two introduced species, the seven-spotted lady beetle (Coccinella septempunctata) and the Asian lady beetle (Harmonia axyridis), in agricultural fields and described multiyear population dynamics. However, the evolutionary dynamics of these interacting species of predatory beetles are uncharacterized. We utilize publicly available multilocus genotype data from geographically disjunct populations of these three species to estimate demography across North American populations. Coalescent analyses reveal (1) a recent (∼4-5 years) decline (>12 fold) in microsatellite effective population size of H. convergens, while expanding (mutation scaled growth rate in 1/u generations = 2910, SD = 362) over evolutionary time scales, (2) a massive (>150 fold), and very recent, effective population size decline in Ha. axyridis, and (3) population size growth (mutation scaled growth rate = 997, SD = 60) over recent and evolutionary time scales in C. septempunctata. Although these estimates are based on genetic data with different mutation rates and patterns of inheritance (mitochondrial versus nuclear), these dynamic and differing population size histories are striking. Further studies of the interactions of these predatory lady beetles in the field are thus warranted to explore the consequences of population size change and biological control activities for evolutionary trajectories in North America.

Predation and Parasitism of Halyomorpha halys (Hemiptera: Pentatomidae) Eggs in Minnesota

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), has spread across North America and is causing serious economic damages. Current management of this pest is based primarily on use of insecticides, which can disrupt integrated pest management programs. Alternatively, biological control is a more benign management tactic. This study provides the first examination of potential impact of parasitoids and predators of pentatomid eggs in Minnesota. Over 2 yr, 10,074 fresh and 9,870 frozen H. halys eggs were deployed in two forest and two soybean habitats in St. Paul, Minnesota from June to August. Our results demonstrate that rates of parasitism and predation were low, accounting for only 0.4 and 3.7%, respectively, across years, habitats, and egg states. In general, the parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae), had higher impacts on H. halys eggs in soybean, and generalist predators were more prevalent in forest habitats. Overall, predation was higher on fresh versus frozen eggs, and parasitism was not consistent across egg states. Although the rates of H. halys mortality due to natural enemies were low, results of our study may be conservative estimates of their true impact. Also, sentinel egg mass surveys should account for undeveloped parasitoids to better quantify H. halys egg mortality by native parasitoids. Alternative management tactics, such as the introduction of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), could be considered to improve biological control of H. halys. Our findings serve as the foundation for future work on biological control of this pest and other pentatomids.

Gut microbiomes of mobile predators vary with landscape context and species identity

Landscape context affects predator–prey interactions and predator diet composition, yet little is known about landscape effects on insect gut microbiomes, a determinant of physiology and condition. Here, we combine laboratory and field experiments to examine the effects of landscape context on the gut bacterial community and body condition of predatory insects. Under laboratory conditions, we found that prey diversity increased bacterial richness in insect guts. In the field, we studied the performance and gut microbiota of six predatory insect species along a landscape complexity gradient in two local habitat types (soybean fields vs. prairie). Insects from soy fields had richer gut bacteria and lower fat content than those from prairies, suggesting better feeding conditions in prairies. Species origin mediated landscape context effects, suggesting differences in foraging of exotic and native predators on a landscape scale. Overall, our study highlights complex interactions among gut microbiota, predator identity, and landscape context.

Scaling up our understanding of non-consumptive effects in insect systems

Non-consumptive effects (NCEs) of predators on prey is an important topic in insect ecology with potential applications for pest management. NCEs are changes in prey behavior and physiology that aid in predation avoidance. While NCEs can have positive outcomes for prey survival there may also be negative consequences including increased stress and reduced growth. These effects can cascade through trophic systems influencing ecosystem function. Most NCEs have been studied at small spatial and temporal scales. However, recent studies show promise for the potential to manipulate NCEs for pest management. We suggest the next frontier for NCE studies includes manipulating the landscape of fear to improve pest control, which requires scaling-up to field and landscape levels, over ecologically relevant time frames.

Spatial and temporal changes in the abundance and compostion of ladybird (Coleoptera: Coccinellidae) communities

Because of their services to agriculture most ladybirds (Coleoptera: Coccinellidae) are intensively studied predators of mainly phytophagous pests. The study of the long-term variation in the composition of their communities was stimulated by recent dramatic changes in the abundance of some species. We review and evaluate possible effects of the main causes cited in the literature. Agricultural and habitat changes (particularly urbanization) affect coccinellid abundance, both negatively and positively. In the temperate zone dominant species occur most frequently associated with abundant prey populations on crops, weeds and planted stands of trees resulting from human activity. Invasive non-native species of coccinellids may endanger native species through intraguild predation or competition for resources, but their supposed serious negative effects on native species can differ considerably. Climatic change may influence coccinellid species in several ways, including indirect effects through lower trophic levels and desynchronisation of the phenologies of host plants, prey and coccinellid populations. In the near future we do not expect climate warming to have important effects on ladybird diversity globally, but local changes in the composition of coccinellid communities and abundance of particular species could occur.

Trap Height Affects Capture of Lady Beetles (Coleoptera: Coccinellidae) in Pecan Orchards

There is scarce information regarding the vertical stratification of predaceous Coccinellidae in tall trees. Although numerous studies have been done in orchards and forests, very few studies have assessed the occurrence of predaceous Coccinellidae high in tree canopies. The objective of this study was to examine the abundance of Coccinellidae at different heights in mature pecan, Carya illinoinensis (Wangenh.) K. Koch, orchards with tall trees. From spring through late fall during 2013 and 2014, yellow pyramidal Tedders traps were suspended in the pecan canopy at 6.1 and 12.2 m, in addition to being placed on the ground (0 m). The exotic species Harmonia axyridis and Coccinella septempunctata accounted for a high percentage of trap capture during this study. Except for Olla v-nigrum, low numbers of native species (Hippodamia convergens, Coleomegilla maculata, Cycloneda munda, Scymnus spp., and Hyperaspis spp.) were captured. However, significantly more were captured in ground traps rather than in canopy traps with the exception of O. v-nigrum. Similar to most native species, significantly more C. septempunctata were captured in ground traps than canopy traps. This contrasts sharply with H. axyridis captured similarly at all trap heights. The ability to exploit resources across vertical strata, unlike many intraguild predators, may be an underestimated factor helping to explain the invasiveness of H. axyridis.

Landscape Factors Influencing Stink Bug Injury in Mid-Atlantic Tomato Fields

Landscape structure and diversity influence insect species abundance. In agricultural systems, adjacent crop and non-crop habitats can influence pest species population dynamics and intensify economic damage. To investigate the influence of landscape factors on stink bug damage in agricultural systems, we assessed stink bug damage from 30 processing tomato fields in the mid-Atlantic United States and analyzed landscape structure and geographic location. We found that forest shape and size, and geographic location strongly influenced stink bug damage. Landscapes with larger forest edge in southern portions of the mid-Atlantic region experienced the greatest damage, perhaps owing to the introduction of the invasive brown marmorated stink bug. We conclude that landscape structure will likely influence damage rates in nearby agricultural fields.

Explicit modeling of abiotic and landscape factors reveals precipitation and forests associated with aphid abundance

Increases in natural or noncrop habitat surrounding agricultural fields have been shown to be correlated with declines in insect crop pests. However, these patterns are highly variable across studies suggesting other important factors, such as abiotic drivers, which are rarely included in landscape models, may also contribute to variability in insect population abundance. The objective of this study was to explicitly account for the contribution of temperature and precipitation, in addition to landscape composition, on the abundance of a widespread insect crop pest, the soybean aphid (Aphis glycines Matsumura), in Wisconsin soybean fields. We hypothesized that higher soybean aphid abundance would be associated with higher heat accumulation (e.g., growing degree days) and increasing noncrop habitat in the surrounding landscape, due to the presence of the overwintering primary hosts of soybean aphid. To evaluate these hypotheses, we used an ecoinformatics approach that relied on a large dataset collected across Wisconsin over a 9-year period (2003-2011), for an average of 235 sites per year (n = 2,110 fields total). We determined surrounding landscape composition (1.5-km radius) using publicly available satellite-derived land cover imagery and interpolated daily temperature and precipitation information from the National Weather Service COOP weather station network. We constructed linear mixed models for soybean aphid abundance based on abiotic and landscape explanatory variables and applied model averaging for prediction using an information theoretic framework. Over this broad spatial and temporal extent in Wisconsin, we found that variation in growing season precipitation was positively related to soybean aphid abundance, while higher precipitation during the nongrowing season had a negative effect on aphid populations. Additionally, we found that aphid populations were higher in areas with proportionally more forest but were lower in areas where minor crops, such as small grains, were more prevalent. Thus, our findings support our hypothesis that including abiotic drivers increases our understanding of crop pest abundance and distribution. Moreover, by explicitly modeling abiotic factors, we may be able to explore how variable climate in tandem with land cover patterns may affect current and future insect populations, with potentially critical implications for crop yields and agricultural food webs.

The Influence of Exotic Lady Beetle (Coleoptera: Coccinellidae) Establishment on the Species Composition of the Native Lady Beetle Community in Missouri

The diversity and abundance of native lady beetles (Coccinellidae) in North America has declined in recent decades. This decline is often correlated with the introduction and establishment of exotic lady beetle species, including Coccinella septempunctata L. and Harmonia axyridis Pallas, suggesting that exotic species precipitated the decline of native lady beetles. We examined species records of native coccinellids in Missouri over 118 yr and asked whether the species composition of the community experienced a shift following the establishment of the exotic species. We found that the contemporary native coccinellid community is different from the community that was present nearly a century ago. However, there was no evidence for a recent abrupt shift in composition triggered by the establishment of exotic species. Instead, our data suggest that the native lady beetle community has been undergoing consistent and gradual change over time, with some species decreasing in abundance and others increasing. While not excluding exotic species as a factor contributing to the decline of native lady beetle species, our findings suggest that other continuous factors, like land use change, may have played a more influential role in determining the composition of the native coccinellid communities within our region.

Influence of Landscape Diversity and Composition on the Parasitism of Cotton Bollworm Eggs in Maize

We deployed >50,000 Helicoverpa armigera eggs in maize fields to assess the rate of parasitism by Trichogramma chilonis across 33 sites during a three-year span (2012–2014) in northern China. Subsequently, we used a partial least squares (PLS) regression approach to assess the relationship of landscape diversity with composition and parasitism potential. The parasitism rate of H. armigera eggs by T. chilonis ranged from 0–25.8%, with a mean value of 5.6%. Landscape diversity greatly enhanced parasitism at all four different spatial scales (0.5, 1.0, 1.5 and 2.0 km radius). Both the proportion of arable area and the total planting area of two major crops (cotton and maize) had a negative correlation to the parasitism rate at each scale, whereas parasitism was positively correlated to the proportion of host crops of H. armigera other than cotton and maize at the 0.5 to 2.0 km radius scales as well as to that of non-crop habitat at the 0.5 and 1.0 km radius scales. The study indicated that maintaining landscape diversity provided an important biocontrol service by limiting H. armigera through the egg parasitoid T. chilonis, whereas rapid agricultural intensification would greatly reduce the presence and parasitism of T. chilonis in China.

Lady Beetle (Coleoptera: Coccinellidae) Communities in Soybean and Maize

Coccinellids provide the most effective natural control of soybean aphid, but outbreaks remain common. Previous work suggests that native coccinellids are rare in soybean, potentially limiting soybean aphid control. We compared the coccinellid community in soybean with that of maize to identify differences in how coccinellid species use these habitats. As maize has long been used by coccinellids in the Americas, we hypothesized that coccinellids native to the Americas would use maize habitats, while exotic coccinellids would be more common in soybean. We identified and quantified aphids and all species and stages of coccinellids in a randomized complete block experiment with four blocks of 10 by 10 -m plots of soybean and maize in central Minnesota during 2008 and 2009. Coccinellid egg masses were identified by hatching in the laboratory. We used repeated-measures ANOVA to identify the dominant species in each habitat and compared species richness and Shannon's diversity with a paired t-test. Aphids and coccinellids had a similar phenology across habitats, but the coccinellid species composition differed significantly between soybean and maize. In soybean, the exotic, Harmonia axyridis Pallas, was the dominant species, while in maize, H. axyridis and the native, Coleomegilla maculata De Geer, were co-dominant. Eggs of H. axyridis were abundant in both habitats. In contrast, C. maculata eggs were very rare in soybean, despite being abundant in adjacent plots of maize. Species diversity was higher in maize. These findings were consistent with other published studies of coccinellid communities in these habitats.

Reproduction in Risky Environments: The Role of Invasive Egg Predators in Ladybird Laying Strategies

Reproductive environments are variable and the resources available for reproduction are finite. If reliable cues about the environment exist, mothers can alter offspring phenotype in a way that increases both offspring and maternal fitness (‘anticipatory maternal effects’—AMEs). Strategic use of AMEs is likely to be important in chemically defended species, where the risk of offspring predation may be modulated by maternal investment in offspring toxin level, albeit at some cost to mothers. Whether mothers adjust offspring toxin levels in response to variation in predation risk is, however, unknown, but is likely to be important when assessing the response of chemically defended species to the recent and pervasive changes in the global predator landscape, driven by the spread of invasive species. Using the chemically defended two-spot ladybird, Adalia bipunctata, we investigated reproductive investment, including egg toxin level, under conditions that varied in the degree of simulated offspring predation risk from larval harlequin ladybirds, Harmonia axyridis. H. axyridis is a highly voracious alien invasive species in the UK and a significant intraguild predator of A. bipunctata. Females laid fewer, larger egg clusters, under conditions of simulated predation risk (P+) than when predator cues were absent (P-), but there was no difference in toxin level between the two treatments. Among P- females, when mean cluster size increased there were concomitant increases in both the mass and toxin concentration of eggs, however when P+ females increased cluster size there was no corresponding increase in egg toxin level. We conclude that, in the face of offspring predation risk, females either withheld toxins or were physiologically constrained, leading to a trade-off between cluster size and egg toxin level. Our results provide the first demonstration that the risk of offspring predation by a novel invasive predator can influence maternal investment in toxins within their offspring.

Effect of Lures and Colors on Capture of Lady Beetles (Coleoptera: Coccinellidae) in Tedders Pyramidal Traps

Purposeful attraction and aggregation of adult Coccinellidae at target sites would be useful for sampling purposes and pest suppression. We field-tested 1) lures in yellow and black pyramidal traps and 2) pyramidal traps that had been painted one or two colors (without lures) to determine if lures or trap color affected capture of adult Coccinellidae. In only one experiment with lures did a single rate of limonene increase trap capture, whereas no other lure ever did. Yellow traps, regardless of using a lure, always captured significantly more lady beetles than black traps. When single-color red, orange, yellow, green, blue, purple, black, and white traps (without lures) were tested, yellow traps captured significantly more lady beetles. Of all species of Coccinellidae captured in these single-color traps, 95% were the exotic species Harmonia axyridis (Pallas) and Coccinella septempunctata L. H. axyridis alone dominated trap capture comprising 74.1% of all lady beetles. Two-color traps (yellow-green, yellow-orange, yellow-white, and yellow-black) never captured more than single-color yellow traps. These results demonstrate that yellow pyramidal traps can be used to purposefully attract, and when used without a collection device, possibly aggregate adult Coccinellidae at targeted field sites.

Survey of Soybean Insect Pollinators: Community Identification and Sampling Method Analysis

Soybean, Glycine max (L.) Merrill, flowers can be a source of nectar and pollen for honey bees, Apis mellifera L. (Hymenoptera: Apidae), wild social and solitary bees (Hymenoptera: Apoidea), and flower-visiting flies (Diptera). Our objectives were to describe the pollinator community in soybean fields, determine which sampling method is most appropriate for characterizing their abundance and diversity, and gain insight into which pollinator taxa may contact soybean pollen. We compared modified pan traps (i.e., bee bowls), yellow sticky traps, and sweep nets for trapping pollinators in Iowa soybean fields when soybeans were blooming (i.e., reproductive stages R1-R6) during 2011 and 2012. When all trap type captures were combined, we collected 5,368 individuals and at least 50 species. Per trap type, the most pollinators were captured in bee bowls (3,644 individuals, 44 species), yellow sticky traps (1,652 individuals, 32 species), and sweep nets (66 individuals, 10 species). The most abundant species collected include Agapostemon virescens F. and Lasioglossum (Dialictus) species (Hymenoptera: Halictidae), Melissodes bimaculata Lepeletier (Hymenoptera: Apidae), and Toxomerus marginatus Say (Diptera: Syrphidae). To determine if these pollinators were foraging on soybean flowers, we looked for soybean pollen on the most abundant bee species collected that had visible pollen loads. We found soybean pollen alone or intermixed with pollen grains from other plant species on 29 and 38% of the bees examined in 2011 and 2012, respectively. Our data suggest a diverse community of pollinators-composed of mostly native, solitary bees-visit soybean fields and forage on their flowers within Iowa.

Landscape-scale pest suppression is mediated by timing of predator arrival

There is increasing evidence that biological control of agricultural pests is affected by the landscape context, although the mechanisms behind this pattern have received little attention. Ecological theory predicts that one key mechanism mediating successful pest suppression is early predator immigration to agricultural fields. However, the importance of this population process under different landscape contexts remains unknown. Here, we elucidate the relative importance of landscape context and timing of predator immigration on aphid suppression by manipulating exposure to predation in agroecosystems located across a gradient of landscape complexity in a subtropical horticultural region in Australia. Aphid suppression varied with landscape context, from populations escaping control to almost complete pest suppression. In general, we found higher aphid suppression when predators were allowed immediate and continuous access to aphids than when predators were delayed or excluded for a week, but responses varied in each landscape. Contrary to previous reports from temperate agricultural landscapes, aphid suppression was neutral or negatively associated with natural and seminatural vegetation, whereas aphid suppression was positively associated with landscapes with a higher proportion of alfalfa. When landscapes were classified according to their levels of complexity, we showed that early predation resulted in similar levels of pest suppression in simplified landscapes (i.e., with low proportions of alfalfa and habitat diversity) as late predation in complex landscapes (i.e., with high proportions of alfalfa and habitat diversity). Our data show that timing of predator arrival to agricultural fields is as important as landscape complexity for mediating pest control in agroecosystems. Furthermore, our results suggest that key distributions of suitable habitats that facilitate natural enemy movement can enhance biological control in simplified landscapes.

Comparison of Relative Bias, Precision, and Efficiency of Sampling Methods for Natural Enemies of Soybean Aphid (Hemiptera: Aphididae)

Generalist natural enemies play an important role in controlling soybean aphid, Aphis glycines (Hemiptera: Aphididae), in North America. Several sampling methods are used to monitor natural enemy populations in soybean, but there has been little work investigating their relative bias, precision, and efficiency. We compare five sampling methods: quadrats, whole-plant counts, sweep-netting, walking transects, and yellow sticky cards to determine the most practical methods for sampling the three most prominent species, which included Harmonia axyridis (Pallas), Coccinella septempunctata L. (Coleoptera: Coccinellidae), and Orius insidiosus (Say) (Hemiptera: Anthocoridae). We show an important time by sampling method interaction indicated by diverging community similarities within and between sampling methods as the growing season progressed. Similarly, correlations between sampling methods for the three most abundant species over multiple time periods indicated differences in relative bias between sampling methods and suggests that bias is not consistent throughout the growing season, particularly for sticky cards and whole-plant samples. Furthermore, we show that sticky cards produce strongly biased capture rates relative to the other four sampling methods. Precision and efficiency differed between sampling methods and sticky cards produced the most precise (but highly biased) results for adult natural enemies, while walking transects and whole-plant counts were the most efficient methods for detecting coccinellids and O. insidiosus, respectively. Based on bias, precision, and efficiency considerations, the most practical sampling methods for monitoring in soybean include walking transects for coccinellid detection and whole-plant counts for detection of small predators like O. insidiosus. Sweep-netting and quadrat samples are also useful for some applications, when efficiency is not paramount.

The impact of prairie strips on aphidophagous predator abundance and soybean aphid predation in agricultural catchments

Reconstructing prairie vegetation in row crop-dominated agricultural landscapes may contribute to several ecosystem services, including the biological control of insect pests, such as the soybean aphid Aphis glycines Matsumura. The influence of the amount and configuration of reconstructed prairie vegetation on the delivery of ecosystem services was investigated in several small catchments at Neal Smith National Wildlife Refuge in Iowa. Treatments include catchments entirely in row crops under a no-till, corn-soybean (Zea mays L.-Glycine max [L.] Merrill) rotation, catchments with 10% of the land in prairie located at the base, and catchments with 10 or 20% of the land in multiple contour strips of prairie. During 2009 and 2011 growing seasons, we measured abundance and diversity of aphidophagous insect predators in response to treatment and habitat type (i.e., soybean, prairie). In 2011, we further studied the biological control of soybean aphids by artificially infesting uncaged and caged plants to prevent exposure from predators. While aphidophagous predators were more abundant in prairie, populations of key aphid predators did not significantly differ among treatments. Biological control of the soybean aphid did not differ among treatments or with distance from prairie. Our results suggest that prairie strips, in addition to providing soil and water quality benefits, may increase the populations of beneficial insects, but may not directly impact biocontrol. We propose several hypotheses to explain why we did not observe more soybean aphid predation with the increased abundance of aphidophagous predators in catchments containing prairie.

Habitat filtering by landscape and local forest composition in native and exotic New Zealand birds

Untangling the relative influences of environmental filtering and biotic interactions on species coexistence at various spatial scales is a long-held issue in community ecology. Separating these processes is especially important to understand the influences of introduced exotic species on the composition of native communities. For this aim, we investigated coexistence patterns in New Zealand exotic and native birds along multiple-scale habitat gradients. We built a Bayesian hierarchical model, contrasting the abundance variations of 10 native and 11 exotic species in 501 point counts spread along landscape and local-scale gradients of forest structure and composition. Although native and exotic species both occurred in a wide range of habitats, they were separated by landscape-level variables. Exotic species were most abundant in exotic conifer plantations embedded in farmland matrices, while native birds predominated in areas dominated by continuous native forest. In exotic plantation forests, and to a lesser extent in native forests, locally co-occurring exotic and native species were segregated along a gradient of vegetation height. These results support the prediction that exotic and native bird species are segregated along gradients related to anthropogenic disturbance and habitat availability. In addition, native and exotic species overlapped little in a multivariate functional space based on 10 life history traits associated with habitat selection. Hence, habitat segregation patterns were probably mediated more by environmental filtering processes than by competition at landscape and local scales.

Biodiversity loss following the introduction of exotic competitors: does intraguild predation explain the decline of native lady beetles?

Exotic species are widely accepted as a leading cause of biodiversity decline. Lady beetles (Coccinellidae) provide an important model to study how competitor introductions impact native communities since several native coccinellids have experienced declines that coincide with the establishment and spread of exotic coccinellids. This study tested the central hypothesis that intraguild predation by exotic species has caused these declines. Using sentinel egg experiments, we quantified the extent of predation on previously-common (Hippodamia convergens) and common (Coleomegilla maculata) native coccinellid eggs versus exotic coccinellid (Harmonia axyridis) eggs in three habitats: semi-natural grassland, alfalfa, and soybean. Following the experiments quantifying egg predation, we used video surveillance to determine the composition of the predator community attacking the eggs. The extent of predation varied across habitats, and egg species. Native coccinellids often sustained greater egg predation than H. axyridis. We found no evidence that exotic coccinellids consumed coccinellid eggs in the field. Harvestmen and slugs were responsible for the greatest proportion of attacks. This research challenges the widely-accepted hypothesis that intraguild predation by exotic competitors explains the loss of native coccinellids. Although exotic coccinellids may not be a direct competitor, reduced egg predation could indirectly confer a competitive advantage to these species. A lower proportion of H. axyridis eggs removed by predators may have aided its expansion and population increase and could indirectly affect native species via exploitative or apparent competition. These results do not support the intraguild predation hypothesis for native coccinellid decline, but do bring to light the existence of complex interactions between coccinellids and the guild of generalist predators in coccinellid foraging habitats.

Graph and circuit theory connectivity models of conservation biological control agents

The control of agricultural pests is an important ecosystem service provided by predacious insects. In Midwestern USA, areas of remnant tallgrass prairie and prairie restorations may serve as relatively undisturbed sources of natural predators, and smaller areas of non-crop habitats such as seminatural areas and conservation plantings (CP) may serve as stepping stones across landscapes dominated by intensive agriculture. However, little is known about the flow of beneficial insects across large habitat networks. We measured abundance of soybean aphids and predators in 15 CP and adjacent soybean fields. We tested two hypotheses: (1) landscape connectivity enhances the flow of beneficial insects; and (2) prairies act as a source of sustaining populations of beneficial insects in well-connected habitats, by using adaptations of graph and circuit theory, respectively. For graph connectivity, incoming fluxes to the 15 CP from connected habitats were measured using an area- and distance-weighted flux metric with a range of negative exponential dispersal kernels. Distance was weighted by the percentage of seminatural area within ellipse-shaped landscapes, the shape of which was determined with correlated random walks. For circuit connectivity, effective conductance from the prairie to the individual 15 CP was measured by regarding the flux as conductance in a circuit. We used these two connectivity measures to predict the abundance of natural enemies in the selected sites. The most abundant predators were Anthocoridae, followed by exotic Coccinellidae, and native Coccinellidae. Predator abundances were explained well by aphid abundance. However, only native Coccinellidae were influenced by the flux and conductance. Interestingly, exotic Coccinellidae were negatively related to the flux, and native Coccinellidae were highly influenced by the interaction between exotic Coccinellidae and aphids. Our area- and distance-weighted flux and the conductance variables showed better fit to field data than area-weighted flux or Euclidean distance from the prairie. These results indicate that the network of seminatural areas has greater influence on the flow of native predators than that of exotic predators, and that the prairie acts as a source for native Coccinellidae. Managers can enhance conservation biocontrol and sustain the diversity of natural enemies by optimizing habitat networks.