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

E. J. Bernklau, B. E. Hibbard, L. B. Bjostad
Journal of applied entomology 2016 v.140 no.10 pp. 725-735
Diabrotica virgifera virgifera, blended foods, corn, death, feeding behavior, food consumption, free fatty acids, fructose, glucose, larvae, liquids, methanol, neonates, phagostimulants, plant extracts, roots, sucrose, synthetic products, toxicity
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.