The effect of rearing larvae of Trichoplusia ni on individual feeding deterrents and on mixtures of deterrents on their subsequent gustatory sensitivity was measured in paired choice leaf disc bioassays. Our working hypothesis was that mixtures of deterrent compounds would mitigate desensitization in phytophagous insects. Neonate larvae were reared on cabbage leaves treated with the feeding deterrents digitoxin, thymol, or xanthotoxin, binary mixtures of these three compounds, or a tertiary mixture until the third larval instar. Deterrence to each compound or mixture was then determined by the leaf disc bioassay. All of the mixtures showed synergistic effects (deterrence) when presented to naïve larvae. Larvae reared on each of the individual antifeedants became significantly desensitized to them except for digitoxin, whereas larvae reared on the mixtures did not become desensitized to the mixtures. Our experiment supports the hypothesis (Jeremy, 1986) that mixtures of deterrents can prevent desensitization, and provides one explanation for the multiplicity of chemical defenses found in many plants.
Species 1: Lepidoptera Noctuidae Trichoplusia ni (cabbage looper)
Keywords: desensitization, feeding deterrents
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA