Field Borders Provide Winter Refuge for Beneficial Predators and Parasitoids: A Case Study on Organic Farms

Mbega

et al. 2022

Insects

Field margins support important ecosystem services including natural pest regulation. We investigated the influence of field margins on the spatial and temporal distribution of natural enemies (NEs) of bean pests in smallholder farming systems. We sampled NEs from high and low plant diversity bean fields using sweep netting and coloured sticky traps, comparing monocropped and intercropped farms. NEs collected from within crops included predatory bugs, lacewings, predatory flies, parasitic flies, parasitic wasps, lady beetles, and a range of other predatory beetles; with the most dominant group being parasitic wasps. Overall, high plant diversity fields had a higher number of NEs than low-diversity fields, regardless of sampling methods. The field margin had a significantly higher number of lacewings, parasitic wasps, predatory bugs, syrphid flies, and other predatory beetles relative to the crop, but beneficial insects were collected throughout the fields. However, we observed marginally higher populations of NEs in intercropping than in monocropping although the effect was not significant in both low and high plant diversity fields. We recommend smallholder farmers protect the field margins for the added benefit of natural pest regulation in their fields.

Section: Discussionsupporting

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Plant-Rich Field Margins Influence Natural Predators of Aphids More Than Intercropping in Common Bean

Mbega

et al. 2022

Insects

“…We detected one female Eu. americanus emerging from an overwintering state in a crop field in central Illinois during April (Clem & Harmon‐Threatt, 2021), and in sampling for flies during spring as part of the 2019 isotope assessment, males were not detected until late May (Appendix S1: Table S2). This information suggests that some Eu.…”

Section: Discussionmentioning

confidence: 99%

Do Nearctic hover flies (Diptera: Syrphidae) engage in long‐distance migration? An assessment of evidence and mechanisms

Clem

Hobson

Harmon‐Threatt

2022

Ecological Monographs

Long‐distance insect migration is poorly understood despite its tremendous ecological and economic importance. As a group, Nearctic hover flies (Diptera: Syrphidae: Syrphinae), which are crucial pollinators as adults and biological control agents as larvae, are almost entirely unrecognized as migratory despite examples of highly migratory behavior among several Palearctic species. Here, we examined evidence and mechanisms of migration for four hover fly species (Allograpta obliqua, Eupeodes americanus, Syrphus rectus, and Syrphus ribesii) common throughout eastern North America using stable hydrogen isotope (δ2H) measurements of chitinous tissue, morphological assessments, abundance estimations, and cold‐tolerance assays. Although further studies are needed, nonlocal isotopic values obtained from hover fly specimens collected in central Illinois support the existence of long‐distance fall migratory behavior in Eu. americanus, and to a lesser extent S. ribesii and S. rectus. Elevated abundance of Eu. americanus during the expected autumn migratory period further supports the existence of such behavior. Moreover, high phenotypic plasticity of morphology associated with dispersal coupled with significant differences between local and nonlocal specimens suggest that Eu. americanus exhibits a unique suite of morphological traits that decrease costs associated with long‐distance flight. Finally, compared with the ostensibly nonmigratory A. obliqua, Eu. americanus was less cold tolerant, a factor that may be associated with migratory behavior. Collectively, our findings imply that fall migration occurs in Nearctic hover flies, but we consider the methodological limitations of our study in addition to potential ecological and economic consequences of these novel findings.

Insect Conserv Diversity

“…Trophic interactions in the form of pesticide‐mediated changes in herbivore community composition (Atwood et al, 2018) and predator preferences were beyond the scope of the current study but deserve further exploration. In the absence of this information, long exposure to contaminated soils during vulnerable life stages—such as overwintering predators in semi‐natural habitats that border agricultural fields (Clem & Harmon‐Threatt, 2021)—may explain the observed loss of predator biomass. The toxicity of neonicotinoids compounds with exposure time (Charpentier et al, 2014; Hayasaka et al, 2019; Suchail et al, 2001) and chronic contact with contaminated soils has been suggested as an important yet understudied route of exposure for taxa with similar life histories (Anderson & Harmon‐Threatt, 2019, 2021).…”

Section: Resultsmentioning

confidence: 99%

Changes in predator biomass may mask the negative effects of neonicotinoids on primary consumers in field settings

Harmon

Harmon‐Threatt

Anderson

2022

1. The non-target effects of pesticides, particularly those that are long-lasting and move easily through the environment, could have community-level impacts on beneficial arthropods and hinder conservation efforts in agrolandscapes 2. We assessed the impacts of a neonicotinoid insecticide, clothianidin, and possible synergisms with a fungicide by quantifying predator, herbivore, and pollinator biomass and morphospecies richness in simulated prairie restorations.3. Predator biomass was 66% lower in plots treated with clothianidin compared to controls and this effect persisted across the growing season. 4. Herbivore biomass was 51% lower in clothianidin-treated plots in June, but the effect waned over the growing season, and no difference was detected in July or August. There was a synergistic effect of clothianidin and fungicide in lowering herbivore morphospecies richness by 12%.