Photoperiodic induction of reproductive diapause and life-history traits of a tortoise beetle, Laccoptera nepalensis (Coleoptera: Chrysomelidae), a range-expanding pest of southern origin

Abstract

The tortoise beetle, Laccoptera nepalensis Boheman (Coleoptera: Chrysomelidae), is an important insect pest of the sweet potato, and is naturally distributed in southern to eastern Asia. The species has recently been expanding its range to the main islands of Japan, where it had previously not been distributed. In this study, the life-history traits of a local population in southern Kyushu, Japan were examined. The adults showed a long-day photoperiodic response at 20 and 25 °C with critical photophases of 13.97 and 12.52 h/day, respectively: female adults reared under long-day conditions laid eggs, whereas those reared under short-day conditions did not and entered diapause. When adults that had been reared under 16L–8D at 20 °C were transferred to 12L–12D at 20 °C, they ceased laying eggs. These results, together with the developmental threshold temperature and thermal constant obtained for each stage, suggest that the beetle overwinters in the adult stage in a state of diapause and produces a maximum of three generations per year in southern Kyushu.