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Gonad maturation in wild Cybister brevis Aubé, 1838 from Japan was investigated to determine the physiological mating season. Breeding experiments showed that hatching occurred from May to September, and the peak was observed in July. The gonadosomatic index (GSI) in collected females (ovary development) showed the highest value in May. The GSIs were low in other seasons. On the other hand, the GSIs in collected males (testes and accessory glands) remained at constant values during the experimental period. Interestingly, high sperm motility was exhibited in May and September, whereas it was low in December and March. This indicates the maturation difference between females and males. Females mature only at the beginning of the breeding season (May), but males do so from May to September. This result suggests that males have a wide-ranging maturation period and earlier sexual maturation than females, ensuring a successful fertilization.
Acknowledgements
The authors would like to thank Y. Hirata (Tokyo, Japan) for helping us to rear insects, Criselda Mae P. Trinidad (Manila, Philippines) for her English review, and two anonymous reviewers for their constructive comments on the manuscript.