Aphids and associated parasitoids exhibit vertical canopy distribution differences in pecans

Authors: SLUSHER, EDDIE KYLE - University Of Georgia; Acebes-Doria, Angelita; Cottrell, Ted; SCHMIDT, JASON - University Of Georgia

Submitted to: BioControl
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2022
Publication Date: 11/27/2022
Citation: Slusher, E., Acebes-Doria, A.L., Cottrell, T.E., Schmidt, J. 2022. Aphids and associated parasitoids exhibit vertical canopy distribution differences in pecans. BioControl. 67:563–570. https://doi.org/10.1007/s10526-022-10169-z.
DOI: https://doi.org/10.1007/s10526-022-10169-z

Interpretive Summary: Insect pest and beneficial populations across different heights on a tree is an important consideration particularly for perennial tree crop systems including pecans. This study investigated the relative difference in the numbers of pecan aphids, parasitized pecan aphids and pecan aphid parasitoids along various vertical points in the pecan tree canopy. Results show that aphid populations, both live and parasitized, were more abundant in the lower parts of pecan trees regardless of tree height. The adult parasitoid populations were more abundant in the lower half of the older, taller (~15 m) trees and in the upper canopy of the young, shorter (~9 m) trees. These implies that monitoring for aphid populations in the lower canopy of trees can provide a good estimate of the aphid population. The capacity of the aphid parasitoid wasps to disperse in the upper canopy may help reduce aphid populations in areas where insecticidal materials cannot be applied through ground-based sprayers.

Technical Abstract: In agricultural systems, aphids (Hemiptera: Aphididae) have been shown to exhibit differences in within plant vertical distribution in vegetation. In addition, natural enemies, such as parasitoids, may have canopy micro-climate preferences. Currently, the within plant vertical distribution of aphids is primarily documented in row crops with few studies in tree systems. Pecan orchards under commercial production range from new to old with variable tree height between these orchards. This height difference highlights the need to examine the vertical canopy distribution of pecan aphids in trees of varying height. In this study, we evaluated the vertical canopy distribution patterns of aphids, parasitized aphids (i.e., mummies), and the primary parasitoid Aphelinus perpallidus (Gahan) (Hymenoptera: Aphelinidae) in pecan trees (Fagales: Juglandaceae) within younger (~'9 m) and older trees (~'15 m). Pecan aphids and mummies were often more abundant in the lower canopy, especially in older trees. Conversely, parasitoid adults were observed at higher abundance in the upper canopy of younger trees in 2021 and in both the lower and upper half of older trees, but there was variability in parasitoid distributions between years. Results indicate that scouting the lower canopy for aphids may be sufficient to estimate populations. The presence of A. perpallidus in the upper canopy can be beneficial as it may allow for biological control in areas where insecticide application may fail.