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

Abstract

SummarySex 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, increäsing 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 attractänt. 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.The results are discussed in relation to mate seeking, together with the mechanisms involved in speciesspecific mating. Key wordsconspecific mating, attraction, sex pheromone, olfactometer, nepetalactol, nepetalactone, Homoptera, Aphidae, Acyrthosiphon pisurn, Aphis fabae, Megoura viciae lntroduction Pettersson (1970aPettersson ( , 1971 and Marsh (1972) first observed that sexual female aphids (oviparae) released a sex pheromone which attracted males. The pheromone was released from scent plaques on the hind tibiae and detected by olfactory sensilla on male antennae. They also reported that

Structure, ratios and patterns of release in the sex pheromone of an aphid, Dysaphis plantaginea

“…Findings are discussed broadly in relation to the biology of the aphid. Dawson et al, 1990;Hardie et al, 1990;Steffan, 1990;Lilley and Hardie, 1996). A similar lack of pheromone specificity has also been reported from field trapping, as a given ratio sometimes catches many species of male aphid (Boo et al, 2000;Goldansaz et al, 2004).…”

“…Oviparae of potato aphids (Macrosiphum euphorbiae) do not display calling behaviour until·2-3 days into the adult stadium (Goldansaz and McNeil, 2003), and the pheromone components A. Stewart-Jones and others were not detected until the second day into the adult stadium for the vetch aphid (M. viciae) (Hardie et al, 1990). Our first day of sampling was on the second day of the adult stadium, and low levels of pheromone were detected.…”

“…Also, Aphis fabae calling behaviour was observed to intensify until day 8 of the adult stadium (Thieme and Dixon, 1996). Similarly, chemical studies that sampled for 24·h periods from M. viciae found pheromone release to be highest on day 6 (Hardie et al, 1990). These slight variations in age-related maximal pheromone output/attractiveness might be species characteristics or may be due to different temperatures used in rearing.…”

“…When sampled by air entrainment, aphid oviparae (sexual females) have been shown to release the two iridoid pheromone components in a ratio that is relatively species-specific (Table·1); however, there are some studies that indicate that ratios change with aphid age (Hardie et al, 1990;Jeon et al, 2003;Goldansaz et al, 2004). Males generally show strongest behavioural responses towards their typical conspecific ratio but some laboratory studies have reported response to a broad range of synthetic ratios and even to a pheromone ratio released by a different species of aphid (Petterson, 1971;Marsh, 1975; Insect communication is primarily via chemicals.…”

“…If nepetalactol and nepetalactone are ubiquitous aphid sex pheromone components, as has been suggested , ratio combinations are limited and additional mechanisms for species isolation are likely to exist. Numerous factors have been proposed and these include the use of different blends of diastereoisomers or enantiomers of nepetalactol and nepetalactone (Campbell et al, 1990;Hardie et al, 1997), the presence of unidentified additional constituents (Guldemond et al, 1993;Lilley and Hardie, 1996), interactions with host-plant volatiles (Petterson et al, 1970a;Campbell et al, 1990;Hardie et al, 1994b;Losël et al, 1996), differences in oviparae colour and species-specific movements (Steffan, 1990), genitalia incompatibility, spatial and seasonal separation of populations (Hardie et al, 1990), and circadian or diel separation of pheromone release (Guldemond and Dixon, 1994;Thieme and Dixon, 1996).…”