Patterns of Behavioural Responses in a Generalist and a Specialist: Lessons for Attract-and-Kill

Abstract

We compared olfactometer responses of a highly polyphagous moth ('Helicoverpa armigera', for which we have a commercial attract-and-kill technology) with those of an oligophagous moth ('Plutella xylostella', for which no similar technology yet exists). For 'H. amigera', 33 out of 38 plants were attractive, including many not suitable for larval development. Only 7 of 34 volatiles from these plants were attractive on their own, and the level of attraction was much lower than the best plants. However, 21 of 31 blends were attractive, and the best of these gave attraction comparable to the best plants. None of these blends mimicked real plants, and some of the best had few components in common. These results are not compatible with the dominant paradigm of ratio-specific attraction to volatiles, mimicking host plants. In field trials, 'H. armigera' could be attracted and killed by many of these non-host blends when they were sprayed on foliage, but would not enter traps baited with them. This suggests a multi-modal response with generalized olfactory mechanisms important only in initial stages. For the brassica specialist 'P. xylostella', two host plants were attractive. Of 12 volatiles tested, only one (a brassica-specific compound) was attractive, but on its own it gave attraction comparable to the host plants. Blending it with other volatiles, including some present in host plants, reduced attractiveness. This suggests a unique volatile response, with perhaps a ratio-specific component to distinguish non-host plants. The implications for developing plant volatile-based attract-and-kill strategies for generalists vs specialists are discussed.