Reverse chemical ecology in a moth: machine learning on odorant receptors identifies new behaviorally active agonists.

The concept of reverse chemical ecology (exploitation of molecular knowledge for chemical ecology) has recently emerged in conservation biology and human health. Here, we extend this concept to crop protection. Targeting odorant receptors from a crop pest insect, the noctuid moth Spodoptera littoralis, we demonstrate that reverse chemical ecology has the potential to accelerate the discovery of novel crop pest insect attractants and repellents. Using machine learning, we first predicted novel natural ligands for two odorant receptors, SlitOR24 and 25. Then, electrophysiological validation proved in silico predictions to be highly sensitive, as 93% and 67% of predicted agonists triggered a response in Drosophila olfactory neurons expressing SlitOR24 and SlitOR25, respectively, despite a lack of specificity. Last, when tested in Y-maze behavioral assays, the most active novel ligands of the receptors were attractive to caterpillars. This work provides a template for rational design of new eco-friendly semiochemicals to manage crop pest populations.

A plant volatile alters the perception of sex pheromone blend ratios in a moth.

Mate finding in most moths is based on male perception of a female-emitted pheromone whose species specificity resides in component chemistry and proportions. Components are individually detected by specialized olfactory receptor neurons (ORNs) projecting into the macroglomerular complex (MGC) of the male brain. We asked how robust ratio recognition is when challenged by a plant volatile background. To test this, we investigated the perception of the pheromone blend in Agrotis ipsilon, a moth species whose females produce a blend of Z7-dodecenyl acetate (Z7-12:Ac), Z9-tetradecenyl acetate (Z9-14:Ac), and Z11-hexadecenyl acetate in a 4:1:4 ratio optimally attractive for males. First, we recorded the responses of specialist ORNs for Z7 and Z9 and showed that heptanal, a flower volatile, activated Z7 but not Z9 neurons. Then, we recorded intracellularly the responses of MGC neurons to various ratios and showed that heptanal altered ratio responses of pheromone-sensitive neurons. Finally, we analyzed the behavior of males in a wind tunnel and showed that their innate preference for the 4:1:4 blend was shifted in the presence of heptanal. Pheromone ratio recognition may thus be altered by background odorants. Therefore, the olfactory environment might be a selective force for the evolution of pheromone communication systems.

Cuticular Hydrocarbon Compounds in Worker Castes and Their Role in Nestmate Recognition in Apis cerana indica.

Differences in cuticular hydrocarbons (CHCs) among worker castes and colonies were examined in Apis cerana indica. The roles of tetracosanoic acid, hexadecanoic acid, pentacosane, and (Z)-9-tricosene in nestmate recognition were studied. The CHC profiles of different castes, i.e., newly emerged bees, nurse bees, and forager bees, were found to differ among colonies. The CHC profiles of nurse bees were similar across different colonies, but forager bees in all colonies had significantly greater amounts of alkanes. In nestmate recognition experiments, guard bees reacted significantly more aggressively to foragers treated with tetracosanoic acid, hexadecanoic acid, and (Z)-9-tricosene. Pentacosane provoked no such effect.

Production of Early Diploid Males by European Colonies of the Invasive Hornet Vespa velutina nigrithorax.

The invasive yellow-legged hornet Vespa velutina nigrithorax was accidentally introduced in Europe in the early 2000s. As is the case in colonies of other wasp and hornet species, V. velutina colonies are known to produce sexuals (males and new queens) at the end of the summer. We show that early-stage colonies in French populations frequently produce males well before the usual reproductive period. The vast majority of the males produced are diploid, which is consistent with the loss of genetic diversity previously reported in introduced populations in France. Since males do not participate in colony activities, the production of early diploid males at the expense of workers is expected to hamper colony growth and, ultimately, decrease the expansion of the species in its invasive range in Europe.