Original aggregation pheromone of the rhinoceros beetle Scapanes australis (Coleoptera, Scarabaeida, Dynastinae)

Scapanes australis is a major coconut pest in Papua New Guinea. Males exhibit a calling behaviour at night by emitting a liquid secretion at the abdomen tip. Attraction of both sexes to calling males was evidenced in field and olfactometer. Slightly greater EAGs were recorded to male than female volatile collections obtained by conventional adsorbent trapping. EAG activity was lost after concentration and GC failed in disclosing male-specific chemicals. Raw male secretion elicited weak but dose-dependent EAGs. Solid phase micro-extraction (SPME) allowed a decisive breakthrough in isolating and identifying the pheromone. A 84:12:4 (w:w) blend of 1: 2-butanol (67:33 (R)-(-):(S)-(+) ratio), 2: acetoin and 3: 2,3-butanediol (43:17:40 (R,R)-(-): (S,S)-(+):meso ratio) characterised the headspace of male secretion. Chemicals were identified by GC-MS using conventional and chiral capillary columns. Synthetic racemic 1:2:3 blends (8-300 mg/d) plus sugarcane attracted both sexes (2 females:1 male ratio) in field trapping, catching twice to 4 times more beetles than 1 live male in sugarcane. This prompted us to develop a pheromone-based trapping strategy. Comparisons of all possible blends of 1, 2 and 3 evidenced that optimal catches required 1 + 2 while 3 had no effect. The pheromone is thus a blend of 1 and 2, which are the smallest (74<MW<88) molecules known as insect pheromones to date and totally differ from the pheromones of the related Oryctes spp. (Texte intégral