An herbivore-induced plant volatile from saltcedar(tamarix spp.)is repellent to Diorhabda carinulata (Colepter: Chrysomelidae)

Authors: Gaffke, Alexander; SING, CHARLENE - US Department Of Agriculture (USDA); MILLAR, JOYCELYN - University Of California Agriculture And Natural Resources (UCANR); DUDLEY, TOM - University Of California; BEAN, DANIEL - Colorado Department Of Agriculture; PETERSON, ROBERT - Montana State University; WEAVER, DAVID - Montana State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2020
Publication Date: 7/29/2020
Citation: Gaffke, A.M., Sing, C.E., Millar, J.G., Dudley, T.L., Bean, D.W., Peterson, R.K., Weaver, D.K. 2020. An herbivore-induced plant volatile from saltcedar(tamarix spp.)is repellent to Diorhabda carinulata (Colepter: Chrysomelidae). Environmental Entomology. XX(XX),2020, 1-8. https://doi.org/10.1093/ee/nvaa079.
DOI: https://doi.org/10.1093/ee/nvaa079

Interpretive Summary: The northern tamarisk beetle is an insect used for the control (classical biological control agent) of the invasive plant saltcedar, which is damaging ecosystems throughout the western United States. It was initially thought the beetles could not survive in the southwestern U.S. However, after rapid adaptation to the new environment the beetle expanded its range into the southwestern U.S. There are now concerns the beetle may indirectly impact the endangered southwestern willow flycatcher. A USDA-ARS scientist at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL in collaboration with Montana State University, U.S. Forest Service, Colorado Department of Agriculture, and University of California investigated potential repellent compounds that could be used to prevent these indirect impacts. We determined that a compound produced by saltcedar was repellent to the beetle. Use of this compound for its ability to repel the beetle in a field setting requires further testing; however if successful, it may allow land managers to limit indirect impacts of the beetle.

Technical Abstract: The leaf beetle Diorhabda carinulata Desbrochers (Coleoptera: Chrysomelidae) was introduced into the United States in 1999 for classical biological control of the exotic woody invader saltcedar (Tamarix spp.). However, the recent southern expansion of the range of D. carinulata in the United States has precipitated conflict between proponents of biological control of Tamarix and those with concerns over habitat conservation for avian species. Several semiochemicals that mediate the formation of aggregations by this species have been reported, but no repellent compounds have been identified thus far. Here, we report a new repellent compound, 4-oxo-(E)-2-hexenal, induced by adult D. carinulata feeding on saltcedar foliage. Collection of headspace volatiles, identification of candidate compounds, and electroantennographic analyses indicated that this compound might influence the beetle’s behavior. Behavioral and exposure assays were conducted to test for repellency in adult beetles, and toxicity in adults and larvae. Headspace volatiles were also collected from adult males exposed to 4-oxo-(E)-2-hexenal to determine the impact exposure might have on aggregation pheromone emission. 4-Oxo-(E)-2-hexenal elicited electrophysiological responses in adults of both sexes. Behavioral responses indicated repellency across multiple doses for reproductive D. carinulata adults but not in non-reproductive adults. Exposure assays indicated altered behaviors in first instars and adults, but not in third instars. Collection of headspace volatiles indicated that exposure to 4-oxo-(E)-2-hexenal did not alter emission of the aggregation pheromone by adult males. The continued development and field deployment of this repellent compound may provide a new tool for the management of D. carinulata.