Role of Host Volatiles in Mate Location by the Japanese Pine Sawyer, <I>Monochamus alternatus</I> Hope (Coleoptera: Cerambycidae)

Abstract

We evaluated the responses of male and female Monochamus alternatus Hope (Coleoptera: Cerambycidae) to various terpenes commonly associated with host trees. Electroantennogram (EAG) tests were conducted with 12 plant volatile compounds and ethanol. Antennae of both sexes were highly sensitive to (R)-(+)-alpha-pinene, (+)-3-carene, (-)-beta-pinene, and terpinolene. Both sexes of M. alternatus were attracted by traps baited with (+)-alpha-pinene, (-)-beta-pinene, (+)-3-carene, or terpinolene. Our results support the first of the three-stage hypothesis posed by Ginzel and Hanks that suggests that location of stressed trees by cerambycids involves three stages: (1) both sexes locate larval hosts by using plant volatiles as kairomones; (2) males produces sex pheromones to attract females after both sexes land on the larval hosts; (3) males and female recognize each other by contract pheromones in their epicuticular wax layer. Males and females showed differences in their EAG responses to several compounds, including (R)-(+)-alpha-pinene, (-)-beta-pinene, myrcene, (+)-3-carene, (R)-(+)-limonene, terpinolene, and trans-caryophyllene. In all cases, males exhibited greater sensitivity than females. In laboratory assays, male M. alternatus showed strong preference for 1% (+)-alpha-pinene and 1% (-)-beta-pinene over other compounds. In field assays, traps baited with (+)-alpha-pinene, (-)-beta-pinene, (+)-3-carene, or terpinolene caught more beetles than control traps. We found strong male bias in beetle catches in baited traps and those captured on the stem of stressed trees despite a strong female bias in emerging beetles in 2004. We hypothesize that male M. alternatus are more responsive than females to plant volatiles and that males have more capacity than females in finding mating locations.