Population genetic structure of the rice weevil, Sitophilus oryzae (L.), in Australia: A pest with limited flight dispersal

The rice weevil, Sitophilus oryzae (L.) (Curculionidae), is a globally distributed pest of stored grain, but despite having functional wings it is considered a reluctant flier. An analysis of the population genetics of S. oryzae from all major regions in Australia where grain is grown and stored in bulk revealed limited population structure nationally, despite our expectation that the low levels of flight in this species would impose considerable population structure geographically. Little genetic structure detected in nuclear DNA yet strong mitochondrial DNA structure was found among populations within the growing regions suggesting greater dispersal in males than females. Also, there were low levels of mitochondrial DNA diversity within and among Australian S. oryzae populations. Anthropogenic movement is most likely the reason for the observed lack of isolation-by-distance pattern of gene flow, especially in eastern Australia. The extent of gene flow demonstrated in our study has potential implications for the development and spread of phosphine resistance in Australia. Undoubtedly, selection for phosphine resistance in S. oryzae is occurring in all grain growing regions because of the widespread use of phosphine fumigation, but the level of gene flow demonstrated in Australian S. oryzae suggests that we can expect some spread of resistant insects geographically despite the apparent limited flight in this species.