PS 48-235 - Unmasking the effects of local and landscape factors on natural enemies and herbivore groups in urban agroecosystems

Wednesday, August 9, 2023

5:00 PM – 6:30 PM PDT

Location: ESA Exhibit Hall

Presenting Author(s)

EG

Edith M. Gonzales

Ph.D. student
University of California, Santa Cruz
Santa Cruz, California, United States

Coauthor(s)

MM

Marily Muñoz-Serrano

Undergraduate
California State University,Monterrey Bay
Monterrey, United States
SP

Stacy M. Philpott, Ph.D.

Professor
University of California, Santa Cruz
Santa Cruz, California, United States

Abstract: Insect biodiversity is a significant indicator of agroecosystem health and insects may also play important functional roles within agroecosystems. For instance, natural enemies, such as parasitoids and predators, can regulate herbivores in urban agroecosystems. Yet, the degree to which natural enemies provide ecosystem services may depend on their abundance and richness, as well as on local (within garden) and landscape management characteristics that influence arthropod communities. In this study, we examined how local (e.g., ground cover, floral abundance, plant species richness) and landscape (e.g., urban cover within 2 km) characteristics influence natural enemy and herbivore abundance in urban gardens on the central California coast. We identified a focal crop, Cucurbita pepo (squash, pumpkin etc.), and sampled 10 plants across 21 urban gardens two times during the summer of 2021 with visual surveys. We identified all insects to family and species or morphospecies. We also assessed several garden and landscape features. We then ran general linear models (GLM) guided by the approach of multimodel inference principles to identify significant factors driving arthropod abundances.

We found that neither abundance of natural enemies nor herbivores was influenced by local or landscape variables, however, individual taxonomic groups responded to specific environmental factors. For individual natural enemy taxa, parasitoid abundance decreased with an increase in urban cover (p=0.045), whereas predatory bug abundance marginally increased with urban cover in the landscape (p=0.09). Ant abundance increased with garden size (p=0.07), and the abundance of spiders tended to increase with floral abundance (p=0.08) and tended to decrease with flower species richness (p=0.09). The abundance of non-aphid herbivores did not vary with local or landscape factors, but herbivores in the family Chrysomelidae (e.g., cucumber beetles, flea beetles) were more abundant (p=0.048) in gardens with more flowers but less abundant in gardens with more flowering species (p=0.031). Thus, the natural enemy abundance of individual groups was influenced by local and landscape factors, whereas only local factors influenced the abundance of chrysomelid herbivores. Moreover, examining natural enemy or herbivore groups together masked the individual effects on certain taxa. These results inform our understanding of insect communities in urban agroecosystems. In particular, we highlight which groups of ecosystem service providers and herbivores may be influenced by agricultural management at the local scale for a common garden crop (C. pepo), and therefore influence garden management processes.