Studies on a sex pheromone in Stegobium paniceum (L.) (Coleoptera; Anobiidae)

Abstract

The sex pheromone system of Stegobium paniceum (L.) was studied in the laboratory by means of live female assay experiments as well as extraction of the pheromone from females using solvent and volatilisation techniques. Female beetles were shown to attract only males, which were themselves attractive to neither sex. Female Stegobium were capable of controlled pheromone emission even when body content levels were high. Newly eclosed females contained small quantities of pheromone which reached maximum levels in 6 to 9-day-old insects. Very little emission occurred until females were 2.5-3.5 days old, after which maximum emission rates were reached rapidly between days 3 and 4, the age at which the first mature oocytes were found in the calyx of female ovaries. A series of dilutions of solvent pheromone extracts were bioassayed with males and a theoretical minimum threshold level of response extrapolated to 0.0004 female equivalents. By comparison with a "wild" strain of Stegobium it was suggested that mass rearing over a long period increased male sensitivity to the pheromone but lengthened the period necessary to reach maximum response levels after adult emergence. Mating slightly reduced female pheromone content, but pheromone emission fluctuated markedly after mating for reasons not fully understood. The number of eggs laid per female increased from about 1.5 to over 40 if copulation occurred. Male presence during oviposition increased the percentage of females producing eggs but decreased the number of eggs laid per female of those laying. This reflects decreased fertility of females with age. The antennal sensilla of Stegobium were surveyed by means of light and scanning electron microscopy. The main types present were trichoidea, basiconica, chaetica and coeloconica, and there was no apparent sexual dimorphism of sensilla numbers or distribution. Male antennectomy completely inhibited sex pheromone response and progressive removal of club segments increasingly diminished male response intensity.