Abstract
Pre-release host specificity testing can reliably predict the environmental safety of weed biological control agent (BCA) candidates but typically does not consider their host-finding behavior. Therefore, BCA candidates that do not utilize non-target plants in the field post-release, despite development on such plants in pre-release tests, may be prematurely disqualified for release. We addressed this issue with the seedpod weevil Ceutorhynchus peyerimhoffi, a BCA candidate for the invasive Eurasian mustard Isatis tinctoria. Ceutorhynchus peyerimhoffi weevils, both naive and experienced, were tested for their responses to olfactory, visual, and combined olfactory and visual cues of Braya alpina , Caulanthus heterophyllus, and the US federally listed Boechera hoffmannii. These responses were compared to I. tinctoria or control treatments in a modified Y-tube olfactometer set-up. Na & iuml;ve and weevils with prior experience on I. tinctoria responded with attraction to olfactory, visual, and combined cues of I. tinctoria. In contrast, there was no attraction by either na & iuml;ve or experienced weevils to non-target plant cues, except for attraction to C. heterophyllus combined cues by experienced weevils. Furthermore, visual cues of B. alpina and B. hoffmannii were repellent to experienced weevils, and olfactory cues of B. alpina were repellent to na & iuml;ve weevils. We conclude that C. peyerimhoffi uses visual and olfactory cues to discriminate between its host plant I. tinctoria and North American non-targets. Behavioral host selection studies involving multimodal cues can provide a mechanistic explanation of host selection and complement environmental safety assessments of weed BCA candidates.