Relict diapause in an introduced weevil in New Zealand

Abstract

The Argentine stem weevil Hyperodes bonariensis Kuschel, a stem boring weevil native to the southern part of South America, was first reported in New Zealand in 19271 where it has become a widespread and serious pest of Graminae. Recent investigations2 have demonstrated the existence of reproductive hibernatory diapause induced by a critical photoperiod in the population in Canterbury, New Zealand (latitude 43°39′S). Coincidentally, it was noted that similar ovarian diapause occurs in H. bonariensis found at a corresponding latitude (41° S) in the Bariloche region of Argentina3. Owing to the imminence of the autumnal equinox at diapause induction (early March in both localities), identical daylengths are experienced successively over a wide latitudinal range within a week. In the present report, examination of the New Zealand population at this time, sampled over at 8° range of latitude, revealed a corresponding synchronous induction of diapause without the usual latitudinal and therefore temperature-related shift in critical photoperiod4. This lack of temperature-related shift and the relatively mild winters suggest that the diapause behaviour of H. bonariensis throughout New Zealand is an adaptively inappropriate relict response resulting from the recently arrived weevils cueing into the same photoperiodic seasonality as their South American counterparts, which in regions such as Bariloche, must have evolved diapause behaviour to survive.