Responses of a natural enemy to pest-induced plant volatiles in complex environments

Abstract

Plants produce volatiles in response to attacks by arthropod herbivores, and these volatiles can be used as cues by natural enemies to find their prey. Because these volatiles are within a variety of other odour blends, here referred to as background volatiles, natural enemy response towards prey-associated plant volatiles may be affected. Thus, this research aimed to evaluate the effect of mixing blends of volatiles under controlled conditions on the foraging behaviour of the predatory mite Phytoseiulus macropilis. Moreover, we investigated whether background volatiles and other cues in a release-recapture experiment under semi-field conditions would affect the response of this predatory mite. Mixing the blends emitted by Tetranychus urticae- infested bean plants with uninfested coriander under controlled conditions, led to a preference of predatory mites towards blends emitted by infested-bean alone over the combination. Also, I found that the volatiles of an uninfested mint plant were attractive to the predatory mite when offered against no odour source. Besides, released-recapture experiments showed a low recapture percentage for every combination of plants tested, suggesting that background volatiles from both companion plants and the environment might have hindered P. macropilis in localizing the plants with prey. These results indicate that experiments under semi-field conditions have a higher accuracy in predicting natural enemy behaviour when compared to olfactometer experiments, that in spite of its importance, does not allow us to predict a behaviour under more complex conditions. Keywords: T. urticae. Herbivore-induced plant volatiles. Companion plants. Semi-field experiments.