7‐methylheptacosane is a major component of the contact sex pheromone of the cerambycid beetle Neoclytus acuminatus acuminatus

Male Neoclytus acuminatus acuminatus (F.) (Coleoptera: Cerambycidae) attempt to mate with females only after touching them with their antennae, suggesting that mate recognition is mediated by contact pheromones in the cuticular wax layer of females. Consistent with that hypothesis, males exhibit similar responses to dead females in laboratory bioassays, but not to solvent‐washed dead females with their cuticular hydrocarbons removed. The mating response of males is restored when solvent extracts are reapplied to carcasses of solvent‐washed females, indicating that the contact pheromone is present in solvent extracts. Solvent extracts of the female cuticle contain six methylalkanes that are not present in extracts of males, three of which (7Me‐C 25 , 7Me‐C 27 and 9Me‐C 27 ) constitute almost 40% of the total hydrocarbons. The bioactivity of these three compounds is tested by applying synthetic standards to solvent‐washed carcasses of females and presenting them to males. Standards are tested singly, pairwise and as the complete blend; freeze‐killed females serve as controls. Males attempt to couple with solvent‐washed female carcasses treated with 7Me‐C 27 alone and in combination with 9Me‐C 27 but only the complete blend elicits the same number of mounting and coupling attempts as does the control. These findings suggest that 7Me‐C 27 (7‐methylheptacosane) is the major component of the contact sex pheromone of N. a. acuminatus and that 7Me‐C 25 and 9Me‐C 27 act as synergists.