Accelerated Development and Toxin Tolerance of the Navel Orangeworm Amyelois transitella (Lepidoptera: Pyralidae) in the Presence of Aspergillus flavus

Authors: BUSH, DANIEL - University Of Illinois; Siegel, Joel; BERENBAUM, MAY - University Of Illinois

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2018
Publication Date: 10/28/2018
Citation: Bush, D.S., Siegel, J.P., Berenbaum, M.R. 2018. Accelerated Development and Toxin Tolerance of the Navel Orangeworm Amyelois transitella (Lepidoptera: Pyralidae) in the Presence of Aspergillus flavus. Journal of Chemical Ecology. 44(12):1170-1177. https://doi.org/10.1007/s10886-018-1027-0.
DOI: https://doi.org/10.1007/s10886-018-1027-0

Interpretive Summary: There are over 1.4 million acres of almonds and pistachios planted in California with a farm gate value exceeding $6 billion annually. The primary moth pest of these two crops is the navel orangeworm (Amyelois transitella), and this insect is strongly associated with the fungus Aspergillus flavus. While both species directly damage tree nuts, the fungus also produces aflatoxins, which are potent carcinogens that contaminate the nuts as well. A series of experiments were conducted in order to determine how this fungus improves the growth and survival of navel orangeworm. Our interest was on the ability of A. flavus to detoxify both natural plant defensive chemicals and insecticides. We used two strains of moth, one of which was resistant to pyrethroid insecticides. Growth rates and survivorship of larvae from the pyrethroid-resistant and susceptible moths were measured after growing these insects on almond meal with and without the toxic chemicals. Additionally, fungi were grown in liquid diets containing the toxic chemicals to determine if they could break them down. Adding A. flavus to the diet improved survival and decreased developmental time. Our results support the hypothesis that A. flavus enhances navel orangeworm growth and development and contributes to detoxification of host protective chemicals and synthetic insecticides.

Technical Abstract: There are over 1.4 million acres of almonds and pistachios planted in California with a farm gate value exceeding $6 billion annually. The navel orangeworm (Amyelois transitella) is the most important lepidopteran pest for both crops, and its relationship with the fungus Aspergillus flavus constitutes a facultative mutualism, forming an important pest complex in tree nuts in California. A series of laboratory experiments were conducted with A. flavus focusing on the role played by this fungus in enhancing the growth and survival of navel orangeworms by detoxifying host phytochemicals(bergapten and xanthotoxin) and synthetic insecticides (spinosyns and pyrethroids). Growth rates and survivorship of larvae from a pyrethroid-resistant (R347) and a susceptible (CPQ) strain were measured on potato dextrose agar (PDA) diet containing almond meal with and without the toxic chemicals. Additionally, fungi were incubated in liquid diets individually containing each of the four test chemicals, and larvae were reared on almond PDA containing extracts of these fungal diets. Adding A. flavus to the diet improved survival and decreased developmental time. This had the greatest impact when larvae were exposed to xanthotoxin, but the addition of the fungus also improved survival for navel orangeworm resistant to pyrethroid insecticides. Our results support the hypothesis that A. flavus enhances navel orangeworm growth and development and contributes to detoxification of host phytochemicals and synthetic insecticides.