Aggregation pheromones of two geographical isolates of the New Guinea sugarcane weevil, Rhabdoscelus obscurus

The aggregation pheromones were studied from two geographical isolates (Hak alau, Hawaii, and Silkwood, Queensland, Australia) of the New Guinea sugarc ane weevil, Rhabdoscelus obscurus. Coupled gas chromatographic-electroanten nographic detection (GC-EAD) and GC-mass spectrometric (MS) analyses of Por apak Q volatile extract from male and from female Hawaiian R. obscurus reve aled a single EAD-active, male-specific candidate pheromone, which was iden tified as 2-methyl-4-octanol (1). Corresponding volatile analyses from male and from female Australian R. obscurus consistently revealed three EAD-act ive, male-specific candidate pheromone components that were identified as 1 , (E2)-6-methyl-2-hepten-4-ol (rhynchophorol) (2), and 2-methyl-4-heptanol (3). In field experiment 1 in Hakalau, Hawaii, traps baited with a stereois omeric mixture of synthetic 1 (3 mg/day) plus sugarcane captured more weevi ls than did traps baited with 1 or sugarcane alone or no bait, indicating t hat 1 is the pheromone of the Hawaiian R. obscurus population. In field exp eriment 2, conducted in Silkwood, Australia. traps baited with stereoisomer ic mixtures of synthetic 1, 2. and 3 (3 mg/day each) plus sugarcane caught more weevils than did unbaited traps or traps baited with 1, 2, and 3 or su garcane. Testing candidate pheromone components 1, 2, and 3 in experiments 2-5 in all possible binary, ternary, and quaternary combinations with sugar cane. indicated that 1 and 2 in combination, but not singly, are pheromone components of the Australian R. obscurus population. Weevils from several l ocations in Australia and Hawaii could not be differentiated using traditio nal morphological characters or ultrastructural comparisons with scanning e lectron microscopy (SEM). However, comparisons of mtDNA sequences (cytochro me oxidase I: regions 11 to M4; 201 base pairs) revealed 5.5% variation bet ween the Hawaiian (N = 2) and the Australian (N = 4) samples. There was no intrapopulation variation in sequence data from the weevils from Hawaii ver sus Australia, suggesting that they are sibling species.