Effects of temperature on mating duration, sperm transfer and remating frequency in Callosobruchus chinensis.

Insect body temperature is usually determined by ambient temperature. Therefore, most biochemical and physiological processes underlying behavioural patterns are temperature dependent. Mating duration is also dependent on temperature, and therefore temperature should influence on sperm transfer and female remating frequency. In the adzuki bean beetle, Callosobruchus chinensis, we found negative relationships between ambient temperature and mating duration, sperm transfer and sperm transfer duration. Female remating frequency at lower temperature (17 degrees C) was lower than at other temperatures (25 degrees C and 33 degrees C). The physiological and behavioural significance of these results is discussed. The number of ejaculated sperm was significantly lower at 33 degrees C than at 17 degrees C; the effect of temperature on sperm transfer is discussed in relation to the intensity of female refusal behaviour directed against males.

Katsuki M ，Miyatake T 《JOURNAL OF INSECT PHYSIOLOGY》

Intra-specific variation in female remating in Callosobruchus chinensis and C. maculatus.

The effects of mating duration on female remating (exp. 1) and under different male densities (exp. 2) were examined in two strains of the adzuki bean beetle, Callosobruchus chinensis and in one strain of the bruchid beetle, C. maculatus. In experiment 1, the frequency of female remating was markedly different between the two strains of C. chinensis. Females of the jC strain, reared long-term in the laboratory, did not remate after being allowed to mate freely (=monogamy), whereas females of the isC strain, recently established from the field, showed high remating frequencies (=polyandry). In both strains, the frequency of female remating increased after the duration of the first mating was deliberately shortened. The relation between mating duration and remating frequency was significantly different, however, between the two strains. In a closely related species, C. maculatus, which manifests polyandry, this relation was more similar to that of the field-derived (=isC) than to that of the laboratory-derived (=jC) strain of C. chinensis. The reasons for the inter-strain variation observed in the remating frequencies of C. chinensis are also discussed. In experiment 2, the mating duration of the three strains was compared under different male densities. Only the lab-derived strain demonstrated a significantly shorter mating duration when one female was placed together with five males than when paired with one male. The shorter mating duration (approximately 26 s) was similar to that of females allowed to remate in the monogamous strain in experiment 1.

Miyatake T ，Matsumura F 《JOURNAL OF INSECT PHYSIOLOGY》

Intra-specific variation in strategic ejaculation according to level of polyandry in Callosobruchus chinensis.

Optimal sperm allocation should differ according to the level of polyandry within a population, because the risk of sperm competition depends on the re-mating frequency of females. We compared the number of sperm ejaculated by males into the female reproductive organ between strains with different levels of polyandry in the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae) when males were reared in different larval densities in a bean. The results showed that males derived from a population with a higher level of polyandry increased ejaculatory expenditure when they were reared under higher larval densities. We discuss the evolutionary correlation of ejaculatory expenditure to the level of polyandry.

Yamane T ，Miyatake T 《JOURNAL OF INSECT PHYSIOLOGY》

Inhibition of female mating receptivity by male-derived extracts in two Callosobruchus species: consequences for interspecific mating.

We investigated the effects of injecting male-derived extracts on congeneric female receptivity in two species of Callosobruchus beetle, C. chinensis and C. maculatus. We also examined the influence of interspecific mating on female remating behaviour in these two species. Male-derived extracts reduced congeneric female receptivity in both species. As quick-acting components, extracts of C. chinensis male seminal vesicles reduced the receptivity of C. maculatus females, whereas extracts of C. maculatus male testes reduced the receptivity of C. chinensis females. As slow-acting components, extracts of male accessory glands of other species reduced the receptivity of both C. maculatus and chinensis females. After interspecific mating, the sperm of C. maculatus males were transferred to the reproductive organs of C. chinensis females, thereby reducing their receptivity. In contrast, no C. chinensis sperm were transferred to the reproductive organs of C. maculatus females; accordingly, the latter's receptivity was not reduced. Furthermore, the survival rate of C. chinensis females decreased markedly after interspecific mating. These results raise the possibility that under circumstances where populations of these two species share the same habitat, reproductive interference would occur only in the interactions between C. maculatus males and C. chinensis females.

Yamane T ，Miyatake T 《-》

Costs of mating and egg production in female Callosobruchus chinensis.

Costs of reproduction include the costs of mating and egg production. Specific techniques such as irradiation or genetic mutation have been used to divide the expense into costs of mating and egg production in previous studies. We tried to divide the costs in the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae), which needs some kinds of bean as an oviposition substrate. Mated females that were not allowed to lay eggs had a shorter life span than virgin females, but they had a longer life span than mated females that were allowed to lay eggs. The results showed two independent significant costs, mating and egg production, on the life span in C. chinensis. Costs of mating, however, include the costs of sexual harassment by males and copulation itself, and we need further studies to divide the costs. The present method for dividing the cost of reproduction into costs of mating and egg production can be applied to a broad taxonomic range of insect species, and thus it will be a useful model system for inter-specific comparisons of costs of mating and egg production.

Yanagi S ，Miyatake T 《JOURNAL OF INSECT PHYSIOLOGY》