Identification of Two Sex Pheromone Components of the Potato Aphid, Macrosiphum euphorbiae (Thomas)

Abstract

Females of the potato aphid Macrosiphum euphorbiae exhibit typical calling behavior, with virgin female oviparae raising their back legs off the substrate to release sex pheromone from glands on the tibia. Airborne collections from calling oviparae were analyzed by GC and GC-MS to determine if, like the majority of aphids examined to date, they produced (1R,4aS,7S,7aR)-nepetalactol (1) and (4aS,7S,7aR)-nepetalactone (2). Both components were present and produced in ratios that varied with age from 4:1 to 2:1. The relative stereochemical configurations of these components were determined by GC-coinjection of the aphid-derived sample with synthetic standards on both HP-1 and DB-Wax GC columns. The absolute stereochemical configuration of the nepetalactol (determined from approximately 15 microg of material in an air entrainment sample) was determined as (1R,4aS,7S,7aR)-1 by derivatization of the aphid sample with (S)-(+)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride (Mosher's acid chloride) to generate a diastereoisomer that was compared to synthetic samples by NMR spectroscopy and GC. In bioassays in the wind tunnel, M. euphorbiae males responded to potato plants with oviparae but not to unattacked plants or those infested with parthenogenetically reproducing apterae. In no-choice laboratory bioassays, the same level of male response was observed to virgins and to the 3:1-5:1 synthetic blends of nepetalactol (1):nepetalactone (2). However, the time taken to reach the source was significantly less to virgin females than to the synthetic pheromone blends. In all cases, males walked rather than flew to the source. Males showed lower responses to a 1:1 synthetic mixture and did not respond to either of the components when presented alone. Under field conditions, few M. euphorbiae males were captured in traps baited with different ratios of the synthetic pheromone. Possible reasons for the different responses under laboratory and field conditions are discussed.

Sex Pheromone of the Soybean Aphid,Aphis glycinesMatsumura, and Its Potential Use in Semiochemical-Based Control

“…Thus far, pheromones have been identiÞed from Ͻ15 aphid species worldwide , Boo et al 2000, Goldansaz et al 2004). All reported aphid pheromone structures are comprised of either a mixture of the monoterpenoids (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol or one of these two compounds alone, except the damson-hop aphid, Phorodon humili, which uses only (1S and R,4aR,7S,7aS)-nepetalactol as its pheromone (Birkett and Pickett 2003).…”

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

“…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). 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.…”

“…By sampling 24 times per day, we have certainty in our measurements, and the low variability in our dataset does support the idea that species-specific ratios are an important component of intraspecies recognition. Interestingly, the two other studies in which ratios have been quantified over age also report a slight decrease in the relative amount of nepetalactol with age (Jeon et al, 2003;Goldansaz et al, 2004). There may be a biological function for this change -for example, to optimise attractant or aphrodisiac properties of the pheromone -as suggested by Hardie et al (Hardie et al, 1990).…”

“…H NMR spectroscopy was performed using a pulse angle of 30°, an acquisition time of 5T1 (with T1 measured to be 2.5·s) and a delay of 5·s. The NMR analysis was compared to diastereoisomeric derivatives from the two enantiomers of synthetic nepetalactol (1 and 2), and full details are described elsewhere (Goldansaz et al, 2004).…”

“…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.…”