No abstract

2-Ethyl-3,5-dimethylpyrazine is an isomer of 2-ethyl-3,6-dimethylpyrazine, the alarm pheromone component of the red imported fire ant, Solenopsis invicta Buren. The pyrazine was synthesized and its alarm activity was investigated under laboratory conditions. It elicited significant electroantennogram (EAG) activities, and released characteristic alarm behaviors in fire ant workers. The EAG and alarm responses were both dose-dependent. Two doses of the pyrazine, 1 and 100 ng, were further subjected to bait discovery bioassays. Fire ant workers excited by the pyrazine were attracted to food baits, and their numbers increased over time. Ants displayed very similar response patterns to both low and high doses of the pyrazine. The pyrazine impregnated onto filter paper disc attracted significantly more fire ant workers than the hexane control for all observation time intervals at the low dose, and in the first 15 min period at the high dose. The pyrazine loaded onto food bait directly tended to attract more fire ant workers than the hexane control. These results support the potential use of 2-ethyl-3,5-dimethylpyrazine to enhance bait attractiveness for the control of S. invicta in invaded regions.

Chemoreceptive sensilla are abundantly distributed on antennal lamellae of scarab beetles. Olfactory reception by these sensory lamellae plays a major role in feeding behaviors and sexual communication of these beetles. A new electroantennogram (EAG) recording technique is here described for evaluation of electrophysiological responses of antennal lamellae of Pseudosymmachia flavescens to sex pheromones and host plant-related compounds. EAG responses were recorded simultaneously from each lamella and the closed antennal club. All test stimuli elicited similar EAG depolarization profiles in all the three lamellae and the closed club although EAG amplitudes from the same lamella or the club varied widely among different chemical stimuli. The mid lamella tended to produce significantly greater EAG responses. EAG responses evoked by a sex pheromone component, anisole, showed a significant correlation with the density of sensilla placodea subtype 1 (SP1). However, no general patterns were obtained for correlations between the density of any test sensilla type and EAG amplitudes evoked by all the six plant volatiles. Single sensillum recordings are needed to elucidate the specific roles of these sensilla in intraspecific sexual communication and perception of host plant volatiles.