Assessing olfactory and visual cues involved in the host selection behavior of the potential biological control agent Mogulones borraginis to improve pre-release host range predictions

While much of pre-release host range testing focuses on differing test conditions to either assess the fundamental host range (no-choice) or the realized host range (choice and field tests), little research is directed at the underlying cues triggering or preventing a potential biological control  female’s host choice. This is true for the seed-feeding weevil, Mogulones borraginis (F.), currently proposed as a biological control agent for the Eurasian herbaceous houndstongue, C. officinale, a noxious and invasive weed of western rangelands. Previous pre-release host range tests for M. borraginis have been complicated by the fact that threatened and endangered native North American confamilials could not be obtained and/or propagated under greenhouse conditions or in common gardens. We assessed olfactory and visual host plant attraction of the weevil using houndstongue and two sensitive native confamilial plants in a controlled research (quarantine) facility. We specifically designed two devices for this purpose: 1) a portable volatile collection system (PVCS) for collecting floral and leaf volatile organic compounds (VOCs) in the field, and 2) a double stacked Y-tube (olfactory) device (D-SYD) for assessing behavioral responses of the weevil to olfactory-, visual- or both cues simultaneously. Based on our preliminary data, we suggest that the deployment of chemical ecological techniques in pre-release host range assessments for weed biocontrol agents offers an improvement of current practices because it allows the assessment of risks to sensitive and threatened native plant species reliably based on quantifiable host selection behavior data.