Locomotory responses to olfactory cues during host‐finding can inform environmental safety assessments of biological weed control agents

Abstract

AbstractIn weed biological control programs, the safety assessment of an agent currently relies on no‐choice and choice feeding, development, and oviposition cage tests. However, confined conditions restrict insect behavior, potentially producing false positive host‐use results that can prematurely disqualify agents, reducing opportunities for successful weed biocontrol. To minimize risks of nontarget attack and maximize successful biocontrol outcomes, it is useful to investigate an agent’s pre‐contact responses to olfactory cues from target and nontarget plant species during host‐selection. Here, we tested how the locomotory behavior of the biocontrol agent Mogulones crucifer Pallas (Coleoptera: Curculionidae) differed when exposed to olfactory cues from its host, the invasive herbaceous Cynoglossum officinale L. (Boraginaceae), versus cues from closely related nontarget species. We used olfactometer behavioral assays, comparing M. crucifer responses to volatiles from C. officinale and nontarget plant species. We observed and measured the duration of resting and walking behaviors, as well as frequencies of arrestment or persisted resting, by M. crucifer in response to these odor sources. In total, 22 confamilial plant species were tested, including five species federally listed as threatened or endangered (T&E) in the USA. Mogulones crucifer consistently responded to C. officinale volatiles with greater duration of resting and frequencies of arrestment behavior compared to other plant species. In contrast, M. crucifer behavior was unaffected by odors of confamilials of C. officinale or responded with repellence to these odors in the olfactometer. These data suggest that in the invaded North American range, M. crucifer is unlikely to use nontarget olfactory cues to find or come into contact with tested nontarget plants, including the tested T&E species. Results from this study improve predictions of M. crucifer’s host‐use in the introduced range and illustrate the potential of this novel approach as a component of pre‐release environmental safety assessments of weed biocontrol agents.