Mechanisms underlying the innate attraction of an aphidophagous coccinellid to coriander plants: Implications for conservation biological control

Abstract

Intercropping tomato plants with coriander is known to attract natural enemies of aphids, mostly coccinellids, but the cues involved in such attraction are not yet known. We investigated why coriander plants attract Cycloneda sanguinea, a generalist aphid predator. We performed a series of controlled experiments with coriander plants in vegetative and reproductive stages to examine the cues attracting C. sanguinea adults and larvae. In a Y-tube olfactometer, C. sanguinea adults were attracted by coriander volatiles produced during the vegetative plant stage suggesting an innate attraction to coriander. Attraction increased when aphid-infested tomato plants were offered together with coriander plants. Moreover, C. sanguinea females used coriander plants as oviposition sites, regardless of plant stage, which could partially explain the attraction to coriander volatiles during vegetative stage. Larvae hatching on coriander plants without prey were able to find nearby aphid-infested tomato plants within about three days after hatching. Additionally, a diet of coriander flowers increased female survivorship, but oviposition only occurred when females had aphids in their diet. Our results indicate that C. sanguinea adults orient to coriander nearing bloom and then use coriander pollen and/or nectar as a supplementary food before aphids become available. The implications of these findings for conservation biological control are discussed.