Aphid sex pheromone components: Age-dependent release by females and species-specific male response

Abstract

Summary Sex pheromone released by Megoura viciae oviparae was collected and analysed for the quantity and relative amounts of each of the two biologically active components. Pheromone was not produced until the second day of the adult stadium, increasing in quantity up to day 6 and then declining. The ratio of (-)-(1R, 4aS, 7S, 7aR)-nepetalactol: (+)-(4aS,7S,7aR)-nepetalactone pheromone mixture changed from ca 1:5 on days 2-6 after adult moult to 1:12 on days 7 and 8, but returned to the original composition by day 10. The behaviour of male aphids from three species, Aeyrthosiphon pisum, Aphis fabae, and M. viciae, was observed in an olfactometer and in two mating bioassays, using both synthetic and natural sex pheromone. The two active components were combined in ratios which mimicked the pheromone released by these and other aphid species. It was found that: 1. M. viciae males were attracted by the synthetic sex pheromone in the olfactometer, with maximal attraction to the conspecific ratio. On the other hand, A. pisum and A. fabae males did not respond to any pheromone mixtures in the olfactometer. 2. Males of all three species could be induced to attempt copulation with conspecific virginoparae treated with synthetic pheromone (virginoparae reproduce asexually and do not produce the sex pheromone). The response in M. viciae and A. fabae was equivalent to that elicited by natural pheromone released by calling conspecific oviparae, but in A. pisum it was slightly lower. 3. In M. viciae, the relative activities of the nepetalactol and the nepetalactone were reversed in the two assays. Thus the former was more potent in the mating bioassay, the latter in the olfactometer. The nepetalactol appeared to act as an aphrodisiac and the nepetalactone as an attractant. 4. Mating response was greatest at the species-specific ratio of the two components, but males were also significantly responsive to mixtures mimicking the sex pheromone of other species.