Effect of changing temperatures from the spawning and egg stages to the emerging adult stage on the induction of reproductive diapause in females of Pseudaulacaspis pentagona (Hemiptera: Diaspididae)

Overwintering females in the third generation of Pseudaulacaspis pentagona (Targioni Tozetti) (Hemiptera: Diaspididae) entered reproductive diapause with undeveloped ovarian eggs. Ovarian development in females collected before the winter solstice was retarded, but development proceeded normally thereafter. Neither length of photoperiod nor changing photoperiods affected the induction of reproductive diapause. Reproductive diapause of P. pentagona was induced when the temperature decreased to around 20 degrees C from the high temperature conditions of the previous generation spawning and current generation egg stages. A transfer test was conducted to elucidate temperature sensitivity, from 25 degrees C in the spawning and egg stages to 20 degrees C at various developmental stages. The sensitive stage for the induction of reproductive diapause was a few days after the emergence of females. Under natural conditions, first-generation eggs encounter temperatures below 20 degrees C in May and adults encounter the high temperatures in June to July and develop normally. Second-generation insects encounter temperatures of 24 degrees C or higher in July to August and develop normally as adults. In contrast, third-generation eggs encounter temperatures of 24 degrees C or higher in September and the adults encounter temperatures of 22 degrees C or lower in October, and reproductive diapause is induced. This paper will discuss the seasonal adaptations of P. pentagona in relation to regional climate conditions and the voltinism of two or three generations per year.