Pheromone Emission Rate by Rhyzopertha dominica (Coleoptera: Bostrichidae) in Response to Adult Starvation and Presence of Conspecifics

Males of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) produce the aggregation pheromones dominicalure-1 (DL1) and dominicalure-2 (DL2), which attract both sexes of the beetle to food source and for mating. The insect only releases these male-produced pheromones during feeding, and volatile emissions from other insect or plant species are not known to contain DL1 or DL2. Studies have suggested that overcrowding and the nutritional state of the adult could have an important effect upon life history parameters such as longevity, mating, and reproduction in the insect. In the current study, we used quantitative gas chromatographic techniques to examine the effect of temporary starvation and beetle density on pheromone dynamics in the insect. R. dominica males that were unfed immediately before testing released less quantity of pheromones compared with fed insects, but pheromone release returned to normal over time on resumption of feeding. Pheromone signaling in the beetle was affected by the interactions between food quantity and male density. The interactive effect showed that by increasing the quantity of food, thus reducing the density of males per quantity of food, the hitherto low rate of pheromone release observed in the insect was reversed and individual males release more pheromone, and thus a stronger signal for responders, as if they were alone with adequate food. The study also showed that the quantity of pheromone emitted per male declined with increasing beetle density and that this effect is stronger in the presence of other males than of females.