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Title: Toxic and behavioral effects of free fatty acids on western corn rootworm (Coleoptera: Chrysomelidae) larvae

Author
item BERNKLAU, ELISA - Colorado State University
item Hibbard, Bruce
item BJOSTAD, LOUIS - Colorado State University

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2016
Publication Date: 12/20/2016
Publication URL: https://handle.nal.usda.gov/10113/5695364
Citation: Bernklau, E.J., Hibbard, B.E., Bjostad, L.J. 2016. Toxic and behavioral effects of free fatty acids on western corn rootworm (Coleoptera: Chrysomelidae) larvae. Journal of Applied Entomology. 140(10):725-735. doi:10.1111/jen.12312.

Interpretive Summary: Insects typically utilize various chemical and/or physical factors to recognize and accept their hosts. These cues may also be of use in pest management. Feeding behavior, feeding intensity and staying behavior of newly hatched western corn rootworm larvae were evaluated in response to synthetic feeding stimulant blends. The feeding stimulant blends (media) were developed to test the efficacy of free fatty acids to acts as cues and as such contained individual free fatty acids at three different concentrations. The analyses showed that several of the fatty acids significantly increased the percentage of larvae feeding, but did not increase food consumption per larva. Most of the free fatty acids elicited “arrestant” behavior causing the larvae to stay in place. At the lowest dose of the majority of the fatty acids elicited “staying” however at the highest dose many fatty acids were toxic to the larvae. These synthetic blends were also compared with extracted maize root liquid and with a maize root extract. Feeding intensity and staying behavior on both root extracts were significantly greater than on any of the synthetic blends, suggesting the presence of additional compounds in maize roots that serve as feeding cues for western corn rootworm larvae. Knowledge of rootworm chemical ecology will lead to additional management options for this major pest.

Technical Abstract: Feeding behavior, feeding intensity and staying behavior of neonate western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae were evaluated in response to synthetic feeding stimulant blends. All of the treatments contained a 3-sugar blend (glucose:fructose:sucrose, 30:4:4 mg per ml) and one of twelve free fatty acids. Each free fatty acid was tested in this blend at three different concentrations. The addition of the 12:0, 16:0, 16:1, 18:0, 18:1, 18:2 and 18:3 free fatty acids to the sugar blend significantly (P < 0.05) increased the percentage of larvae feeding, but did not increase food consumption per larva. Most of the free fatty acids elicited arrestant behavior. At the lowest dose (0.1 mg per ml) all of the free fatty acids except the 18:0 and the 20:0 elicited “staying” by significantly more larvae than the sugar blend, and at the highest dose (1.0 mg per ml), eight free fatty acids (8:0 10:0, 12:0, 14:0, 16:1, 18:1, 18:2 and 18:3) caused more larvae to stay compared to the sugar blend. Larvae were visibly impaired after exposure to some of the free fatty acids. At the highest dose, the 8:0, 10:0, 12:0, 14:0, 16:1, 18:1 and 18:2 free fatty acids were toxic to the larvae. At least 60% of larvae were impaired after exposure to the 12:0, 16:1 and 18:2 free fatty acids and the 8:0 and 10:0 free fatty acids caused 100% impairment or death. Synthetic blends were compared with extracted maize root liquid and with a methanol extract of maize roots. Feeding intensity and staying behavior on both root extracts were significantly greater than on any of the synthetic blends, suggesting the presence of additional compounds in maize roots that serve as feeding cues for western corn rootworm larvae.