Aspects of the Behavioural Ccology of Stegobium paniceum (L.) (Coleoptera Anobiidae)

Abstract

Large numbers of individual live insects were followed through their life cycle, and aspects of their behaviour and ecology were the subjects of observation and experiment. The pheromone system (discovered by previous authors) was found to be situated in the female abdomen. The mating efficiency of both sexes was found to increase steadily with age after adult eclosion, reaching a peak at 9 days. Female pheromone production/release was significantly reduced after 3 minutes in copula, as was female receptivity to the male. These phenomena are cumulatively induced by mating and are probably the result of the passage of male accessory gland substance. Eleven main units of male pre-copulatory behaviour are described. An ethogram is given showing the chronological relationships of these units during mating encounters. The use of the male antennae, palps, tarsal claws, and aedeagus during mating and amplexus is related to their morphology and their function in stimulating and being stimulated by the female. Mating experience, while not affecting a male's response to pheromone, does impair his mating efficiency. There is evidence that males learn correct orientation to the female during mating experience. Oviposition begins within 16 hours after copula, and 61% of the eggs are laid within 24 hours. Female age does not affect fecundity, but an increase in age increases the oviposition rate. At least 2-5 minutes in copula are required to stimulate oviposition, but the full term (mean: 61 minutes) is required for 100% fecundity. Specific tactile stimuli are needed to initiate oviposition. Female dispersal is caused by overcrowding and mating. Mating directly causes an increase in female locomotory activity and tendency to fly. The increase in locomotory activity rises proportionately to the length of time in copula. These changes are probably partly produced by the passage of male accessory gland substance. The adaptive significance of these phenomena is discussed. An increased density of eggs causes a corresponding significant increase in the mortality of developing insects. The slight preponderance of female numbers also becomes significant at high population densities. Density-dependent control appears to be the result of cannibalism of the eggs by early larvae. A life table is given of the mean percentage survival at different stages in the life cycle. The largest mortality is at hatching and among early larvae. Thirty-nine percent of larvae did not construct a cocoon. Cocoons have a significant effect on reducing mortality and wing deformation. Cocoons are shown to be adaptively positioned.