COS 134-2 - Effects of isolated red oak foliar phenolics on Lymantria dispar growth and behavior

Tuesday, August 8, 2023

3:45 PM – 4:00 PM PDT

Location: D138

Presenting Author(s)

BR

Brian J. Rehill

Professor
United States Naval Academy, United States

Coauthor(s)

AL

Amanda Lau

Physician
United States Naval Academy, United States
AH

Adam Hammer

United States Naval Academy, United States
AK

Amy Krick

Surface Warfare Officer
United States Naval Academy, United States
LM

Lianne Marquez

United States Naval Academy, United States
EK

Erin Kusuda

United States Naval Academy, United States
HA

Hazel Acosta

Surface Warfare Officer
United States Naval Academy, United States
CT

Caitlyn Thompson

Surface Warfare Officer
United States Naval Academy, United States
VM

Venus Molony

United States Naval Academy, United States

Abstract: Outbreaks of forest defoliators have effects at community, ecosystem and landscape levels. Lymantria dispar, an invasive forest defoliator in North American, undergoes irruptive outbreaks on 10-12 year cycles, and these cycles appear to be controlled by interactions among the defoliating larvae, natural enemies including a species-specific virus (LdNPV), and induced plant defenses. To better understand the irruptive outbreaks of Lymantria dispar, we performed a series of experiments investigating the interactions between Lymantria dispar larvae and one of their preferred host plants, red oak (Quercus rubra). Chromatographically separated fractions of red oak leaf phenolics were added to artificial diet and fed to neonate larvae for periods of 12-14 days. In three of the four feeding experiments, larvae gained 30-40% less fresh mass with diets amended with the most non-polar red oak phenolics versus the unamended diet, but in one experiment this pattern was reversed. Further experiments demonstrated that the unusual response was due to the larvae used, and that significant variation in response to artificial diet exists among larvae from different parents. Behavioral assays indicated that larvae feeding diet amended with the least polar fractions move more than larvae feeding on the control (unamended artificial diet). Thus it appears that higher concentrations of less polar phenolics in red oak leaves may cause gypsy moth larvae to move more frequently, making them more likely to encounter LdNPV, be infected, and die. This may explain why induced defenses in host plants of Lymantria dispar can lead to higher mortality due to the LdNPV.