Identification of a receptor for the sex pheromone of the vine mealybug, Planococcus ficus

Authors: Corcoran, Jacob; Mahaffee, Walter - Walt

Submitted to: Current Research in Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2024
Publication Date: 1/25/2024
Citation: Corcoran, J., Mahaffee, W.F. 2024. Identification of a receptor for the sex pheromone of the vine mealybug, Planococcus ficus. Current Research in Insect Science. https://doi.org/10.1016/j.cris.2024.100072.
DOI: https://doi.org/10.1016/j.cris.2024.100072

Interpretive Summary: Grapevine leafroll disease is one of the most destructive and economically devastating diseases of the grape industry, worldwide. The disease is caused by several closely related viruses that are transmitted between grapevines by mealybugs. Mealybugs infestations in vineyards can be difficult to detect due to the fact that they spend most of their lives living underneath the bark of grapevines. This characteristic also makes it difficult to efficiently and effectively control mealybugs through traditional methods, such as the use of biological control agents and contact insecticides. Female mealybugs produce species-specific sex pheromones that they release into the environment to attract males during reproductive periods. These molecules can be used in a practice called mating disruption, in which synthetic versions are deployed during these reproductive periods to impair the ability of male mealybugs to find the females, however this control tactic is relatively expensive compared to alternatives due to the high cost of synthetic mealybug pheromones. In this study we identified candidate receptors for the vine mealybug sex pheromone from genetic resources and tested them for their ability to respond to the vine mealybug sex pheromone, as well as several volatiles known to be produced by grapevines, by expressing the receptors in mammalian cell lines. Using this approach we identified one receptor that responds to the common grape volatile, Beta-farnesene, and one receptor that responds to lavandulyl senecioate, the sole constituent of the vine mealybug sex pheromone. Identification of a receptor for the vine mealybug sex pheromone will facilitate high-throughput screening campaigns aiming to identify receptor activators or inhibitors that can be used in mating disruption campaigns, as well as in the development of vine mealybug-detecting biosensors.

Technical Abstract: The vine mealybug, Planococcus ficus, is a significant pest of vineyards in all major grape growing regions of the world. This pest causes significant aesthetic damage to berry clusters through its feeding behavior and secretion of "honeydew", which leads to significant decreases in crop marketability. More importantly, the vine mealybug is a vector of several grapevine viruses which are the causal agent of grapevine leafroll disease, one of the most destructive and economically devastating diseases of the grape industry worldwide. As there is no cure for grapevine leafroll disease the only control measures available to reduce its spread are to remove infected vines whilst simultaneously controlling mealybug populations. Here, using transcriptomic libraries prepared from male and female mealybugs, as well as a draft genome, we have identified and evaluated expression levels of members of the odorant receptor gene family. Interestingly, of the 52 odorant receptors identified from the P. ficus genome, only 12 were found to be expressed in male or female adult mealybugs. Heterologous expression of eight of these receptors, along with the obligate co-receptor, Orco, in HEK293 cells allowed for the identification of two receptors that respond to lavandulyl senecioate, the sole constituent of the sex pheromone used by this species. Interestingly, one of these receptors, PficOR8 also responded to the main component of the sex pheromone used by the Japanese mealybug, Planococcus kraunhiae. The odorant receptor gene expression data presented here represent the first report of this important gene family in soft-scale insects, and the functional data represent the first report of a sex pheromone receptor in a hemipteran insect. The identification of a receptor for the vine mealybug sex pheromone will allow for the development of novel, species-specific pest control tools and monitoring devices.