Crop diversity and within field multi-species interactions mediate herbivore abundances in agricultural landscapes

Authors: KHEIRODIN, ARASH - University Of Georgia; DE TOLEDO, PEDRO FELIPE - University Of Georgia; Simmons, Alvin; SCHMIDT, JASON - University Of Georgia

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2023
Publication Date: 1/2/2024
Citation: Kheirodin, A., De Toledo, P., Schmidt, J., Simmons, A.M. 2024. Crop diversity and within field multi-species interactions mediate herbivore abundances in agricultural landscapes. Biological Control. https://doi.org/10.1016/j.biocontrol.2023.105386.
DOI: https://doi.org/10.1016/j.biocontrol.2023.105386

Interpretive Summary: The abundance of insect pests in agricultural fields may be affected by the particular mixture of crops in the landscape, as well as by the particular mixture of predators that eat the insect pests. We conducted a study to assess the impact that a complex of pests and a complex of predators may have on changes in the population of insect pests in various cotton landscapes. The studied pests were whiteflies and aphids, and the primary predators of these insects in the study were lady beetles, spiders, minute pirate bugs, and big-eyed bugs. Crop diversity directly and indirectly suppressed whitefly and aphid abundances in the fields, and landscape types such as wetlands and pastures promoted aphid abundance. The results indicate that abundance of whiteflies and aphids in the cotton fields depends on landscape complexity and within field interactions among the insects. This information will be useful for the research community to develop strategies to manage whiteflies and aphids in cotton landscapes.

Technical Abstract: Insect herbivore abundances in agricultural fields partly depend on surrounding landscape compositional heterogeneity (i.e., crop and non-crop habitat diversity, and landscape complexity). Landscape complexity can directly (i.e., dilution and concentration of host crops) and indirectly (through promoting herbivore biocontrol rates), regulate herbivore populations in agricultural fields. While the indirect effect on pest populations through promoting biocontrol has been widely studied, one question remains; can landscape complexity could also regulate herbivore populations by mediating within field multi-species interactions among herbivores and their shared natural enemies? For instance, an increase in the abundance of one shared prey (e.g., aphids) may alter predator feeding on whitefly through predator-prey preference or prey switching behavior. Therefore, these within field multi-herbivore-predator interactions can jointly or independently from landscape complexity explain pest control in the agricultural fields, which remain unexplored. During 2019 and 2020, we estimated the abundance of Bemisia tabaci and Aphis gosypii, their dominant predators (coccinellids, spiders, Orius, and Geocoris), and their interaction (using molecular gut content analysis) in 35 cotton fields along a gradient of landscape diversity (0.61 to 0.88 Simpson diversity) across Georgia, USA. We used multi-model inference to select best-fitting generalized linear models to determine scale-dependent landscape complexity effects on the abundance of B. tabaci and A. gosypii, their predators and predation frequency. At the field scale, we assessed the effect of predator abundances, correlation in B. tabaci and A. gossypii abundance, and predation frequency on herbivores on B. tabaci, and A. gossypii abundance in cotton fields. Crop diversity directly and indirectly suppressed B. tabaci and A. gosypii abundances in cotton fields, which suggests crop diversification is a factor in cotton pest control. In addition, cover types such as wetlands and pastures promoted aphid abundance, which suggests context dependency in pest-pest interactions triggered by landscape context. Furthermore, we found a complex interaction among pests at the field scale, with higher aphid abundance correlated with decreased whitefly abundance. Interestingly, higher whitefly abundance potentially resulted in apparent competition with aphids, as evidenced by a reduced predation frequency on aphids. Overall, our study indicates the abundance of whiteflies and aphids in cotton fields depends on the combined effects of landscape complexity and within field species interactions.