Examining olfactory and visual cues governing host-specificity of a weed biological control candidate species to refine pre-release risk assessment

In weed biological control programs, pre-release host-specificity testing relies traditionally on no-choice and choice feeding, oviposition, and development tests. Rarely have they included detailed examination of behavioral responses to olfactory and visual cues of biological control candidates, although a better understanding of the mechanisms underlying host recognition may explain potential discrepancies between choice and no-choice tests, and/or between tests conducted in the lab versus field conditions. We investigated how the seed-feeding weevil, Mogulones borraginis, distinguishes its host plant, Cynoglossum officinale, from three native confamilial non-target species in North America. In behavioral bioassays, M. borraginis responded to olfactory and visual cues individually and, to an even greater extent, to both plant cue modalities when offered simultaneously. In tests with the combined cues, M. borraginis was attracted to C. officinale but responded with indifference or was repelled by non-target plants. In electrophysiological experiments, we identified that M. borraginis responded to ten volatile compounds and four wavelengths of lights from inflorescences of C. officinale. We propose that studies of responses to multimodal plant cues can advance our understanding of how biocontrol candidate species discriminate among host plants and closely related non-target species, thereby increasing the accuracy of environmental safety assessments pre-release.     

Host recognition by Rhinocyllus conicus of floral scents from invasive and threatened thistles

One of the main obstacles of classical biological control is that biological control organisms cannot be recalled once they are released in nature. It is particularly true for the flowerhead weevil, Rhinocyllus conicus Frölich, which was released as a biological control organism for the invasive musk thistle, Carduus nutans L. (MT). While weevils successfully suppressed introduced populations of musk thistles and other invasive thistle species, non-target attacks have been reported on multiple native thistles including federally listed threatened and endangered (T&E) thistle species. To investigate the foraging behavior of female weevils on invasive and native thistles, we examined volatile organic compounds (VOCs) emitted from MT and a T&E plant species, Sacramento Mountains thistle, Cirsium vinaceum Wooton & Standley (SMT) in the Lincoln National Forest, New Mexico. We used a dynamic headspace volatile collection system and gas chromatography-mass spectrometry to compare volatile profiles between MT and SMT. Female weevils reacted to 7 electrophysiologically active chemical compounds in the blends based on gas chromatography-electroantennography. The behavioral response of female weevils was indifferent when VOCs from both thistles were offered in y-tube olfactometry experiments. Yet, they preferred VOCs collected from MT to purified air. The searching time of female weevils was longer to VOCs collected from SMT over controls. Investigating signals during the initial host recognition of released biological control organisms may open new opportunities to reduce non-target attacks on T&E plant species.

     

Evaluating quantum yield and ultraviolet–visible reflectance in baby pumpkins: Implications for oviposition behavior of pumpkin fruit flies

Frugivorous insects utilize both olfactory and visual cues to locate their host plants. Although volatiles have been extensively studied for detecting infested fruits, the role of visual cues in oviposition site selection remains mostly unknown among frugivorous insects. To investigate physiological changes in a host plant, we measured the quantum yield and reflectance of three wavelengths of light (350, 450 and 520 nm) after puncturing the surfaces of commercially grown pumpkins using insect pins during two different seasons outdoors. Quantum yields did not show significant differences between undamaged and simulated oviposition sites. Two wavelengths within the visual spectrum were similar between the two treatments. However, photon counts at 350 nm, in the ultraviolet range, were 1.76 fold higher in simulated oviposition sites than in undamaged sites, which was consistently observed across three field seasons. Considering that frugivorous insects and other phytophagous insects recognize the 350 nm wavelength for host identification and oviposition, we conclude that the disparities in ultraviolet reflectance can serve as a baseline for assessing the actual oviposition response of fruit flies. This finding contributes to the role of visual cues in the oviposition behavior of frugivorous insects and the development of a nondestructive detection method for pumpkin fruit flies.