Christian Y. Oseto

Discrimination of sunflower volatiles by the red sunflower seed weevil

Five principle monoterpenoid and other constituent volatile chemicals of sunflower heads were combined to resemble two lines of sunflower (Helianthus annuus L.): one U.S.D.A. standard line and one French line which was ‘poorly visited by insects’ (Etievant et al., 1984). Field trials of attraction to red sunflower seed weevils (Smicronyx fulvus Le Conte, Coleoptera: Curculionidae) showed that one was clearly preferred over the other. The more attractive mixture contained α‐pinene, β‐pinene, limonene, camphene and bornyl acetate in a ratio resembling that of Flath et al. (1985) rather than that described by Etievant et al. (1984). One or two volatiles were deleted from the optimal blend but only mixtures of five volatiles showed the highest attraction. Substitution of sabinene, another volatile prominent in sunflower, for one of the five in the optimal blend also decreased attraction of seed weevils. When the monoterpenoid components and ‘green leaf volatiles’ in the traps resembled the ratios of most of the prominent volatiles of sunflower, attraction was significantly greater than controls.

Structure of the stridulatory apparatus and analysis of the sound produced by Smicronyx fulvus and Smicronyx sordidus (Coleoptera, Curculionidae, Erirrhininae, Smicronychini)

Wing folding spicules, elytral binding patches, and elytral locking devices of adult male and female seed weevils, Smicronyx fulvus LeConte and S. sordidus LeConte, involved in stridulation are described. Sound is produced by both sexes of the two species when the plectrum, paired conical teeth located along the anterior margin of the dorsally elevated seventh sternite, is struck against an elongate file, the pars stridens, on the under surface of the apical portion of each elytron. A second plectrum, on the sixth tergite, is well‐developed in males of both species and is used by males to produce sound before and during mating.