How important is vision in short-range host-finding by Trichogramma ostriniae used for augmentative biological control?

Abstract

ABSTRACTAlthough the scientific literature is replete with reports that host and plant volatiles elicit behavioural responses in Trichogramma, most do not compare the relative importance of olfaction, vision, or their interaction; this may be an oversight. We conducted experiments to evaluate whether vision, odour, or their interaction mediated host location by T. ostriniae over small spatial scales. T. ostriniae were given choices between odour cues and visual cues from Ephestia kuehniella, Ostrinia nubilalis, Manduca sexta, and polymer and glass beads, or between visual cues with and without an odour component. There generally was no preference for an odour component, suggesting that random encounter or visual guidance was the likely mechanism of location. For females who successfully located a cue, we found little evidence that odour was the primary mode of detection. However, when M. sexta eggs were the odour source, and compared to eggs washed with solvent to remove volatiles, females showed a predilection toward visual cues with an odour component. However, when Manduca spp. moth scales were applied to glass beads under conditions of high visual contrast, there was no significant preference for odourised visual cues. There is little doubt that Trichogramma rely on olfaction, but many studies include no visual components, no evaluation of the magnitude of olfaction relative to vision nor their interaction. We offer that random movement and vision may determine much of host-finding, especially with Trichogramma augmentatively released into monocultures, but there is likely some interaction with odours at some small spatial scale.