Comparative developmental and reproductive biology of geographical populations from two cryptic species in Brontispa longissima (Coleoptera: Chrysomelidae)

Brontispa longissima is a serious pest of the coconut palm Cocos nucifera, presumed to have originated in Papua New Guinea and Indonesia. It recently invaded Southeast and East Asia, where outbreaks have been reported. Mitochondrial DNA analysis reveals two cryptic species in B. longissima: one is distributed over a wide area including Asia and the Pacific region (the Asian clade) and the other in a limited area in the Pacific region (the Pacific clade). Recent invasions and outbreaks have been reported only from the area where the Asian clade has been found, suggesting that this clade has become a pest in Asia. To infer if the Asian clade has the ability to establish, spread and outbreak in novel habitats more effectively than the Pacific clade, we compared life-history traits between the two populations of different clades. The net reproduction rate (R-0) was 130.0 and 94.0, the mean length of a generation (T) was 57.7 and 54.7 days, and the intrinsic rate of natural increase (r) was 0.084 and 0.083 per day for the population from Ishigaki Island, Japan (ISH) (the Asian clade) and for the population from Papua New Guinea (PNG) (the Pacific clade), respectively. Although the difference in r was little, the simulated population growth showed that the ISH population can be 1.6 times larger than that of the PNG after ten generations. The rapid population growth of the Asian clade would be partly responsible for its establishment, spread and frequent outbreaks in Asia.