Settlement decisions of twospotted spider mites: Using behaviour and electrophysiology to understand the role of silk-bound chemical cues

Twospotted spider mites (Tetranychus urticae), are phytophagous pests that cause damage to crops around the world. These mites produce silk, which is used for protection, to support movement and dispersal, and as a substrate for pheromones. Previous work has shown that 1-day old mated females respond to conspecific silk cues when choosing a microhabitat, preferring to settle in the presence of conspecifics and thus increasing the chance of survival. However, the identity of the semiochemicals present on silk is yet unknown. We replicated and extended previous behavioural results using the same two-choice assay, in which mites had the choice to settle on a section of a bean leaf which had silk covering one half and no silk on the other half. We confirmed that 1-day old female mites significantly preferred to settle in the presence of silk laid by other adult females and that older adult females had the same response. Furthermore, male mites also showed a significant response to silk produced by females, but not to the silk of other males. To determine the chemicals that may be responsible for mite responses to female-produced silk, we will use gas-chromatography/mass-spectrometry and coupled gas-chromatography electro-tarsography. Compounds that elicit electrophysiological responses when passed over chemoreceptors on the tarsi of mites will be identified and then tested for behavioural responses. This research is important in understanding the mechanisms underlying chemo-detection and settlement decisions by spider mites and may help to inform and implement more precise pest management strategies.