Reproductive Behaviour of the Lesser Waxmoth, Achroia Grisella (Pyralidae: Galleriinae): Signalling, Pair Formation, Male Interactions, and Mate Guarding

Field: Agricultural and Biological Sciences (Life Sciences)

Laboratory experimentation and field observations of the lesser waxmoth revealed marked differences in reproductive behaviour from other Lepidoptera. Males emit a long-range signal, stationary wing-fanning combined with release of a 2-component pheromone, continuously during scotophase. Pheromonal release rates are 10-1000 x those known for female-emitted pheromones in other moths. However, the energetic cost of wing-fanning is very low relative to known values for similar activities in other male insects. In the field, signalling occurs in the vicinity of the larval food resource, beehives, the precise location (within or on the exterior of the hive) depending on the honeybee population size. Matings were observed during the initial half of the night. During pair formation, females usually run directly toward a signalling male. Female approach behaviour at close range is rather unstereotyped. They may directly contact the male, wing-fan and/or circle in close proximity, or remain stationary until the male initiates courthip. When provided with a choice of a wing-fanning male and a non-wingfanning one separated by > 10 cm, females always approach the wing-fanning individual. If only non-Wing-Fanning males are present, young females never approach, but older females, which typically move more extensively than younger individuals, sometimes approach and mate. Males in close proximity to one another, whether in laboratory chambers or at beehives, interact in various ways. A higher proportion of males in groups signal than solitary males, and when the first male in a group begins signalling, the other moths initiate signalling shortly thereafter. Nevertheless, a small proportion of males signal infrequently or not at all, and these males sometimes remain very close to signallers. When a female is presented with a pair of males as above, she occasionally mates with the non-signaller. In these circumstances, the non-signaller responded to the female's close-range approach and began wing-fanning. Non-signalling males do not enjoy greater longevity in the laboratory, despite their reduced consumption of energy. Aggregated males fight by running, while wing-fanning, at neighbours. The respondents of such attacks are usually signalling males. Males usually resume signalling soon after copulation. Individuals that remate within a short period remain in copula for a very extended length of time. These extended copulations occur because the male cannot immediately transfer a spermatophore, and therefore comprise a form of pre-fertilization mate guarding. Females show no preference for virgin or previously-mated males and do not attempt to interrupt extended copulations. The unusual system, for Lepidoptera, of pair formation in the lesser waxmoth is viewed as a response to an aggregated resource structure which renders searching for mates relatively low in risk and expenditure of energy. Consequently, females assume this role. The other non-lepidopteran aspects of the mating system evolved as a result of this sex-role reversal in pair formation and the aggregation of adult males at the larval food resource.