Genetic relations between outbreaks of the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera : Tephritidae), in Adelaide in 2000 and 2002

The Queensland fruit fly (Q-fly), Bactrocera tryoni, is a serious horticultural pest throughout eastern Australia, and apart from isolated outbreaks, is absent from Adelaide and South Australia. Considerable resources are put into preventing the entry of Q-fly into South Australia and the eradication of any outbreaks. Nevertheless, some flies are still trapped in Adelaide and, because known permanent populations are too distant for unaided dispersal, these flies must arrive as larvae in infested fruit. To provide authorities with more information on the nature of and the extent of outbreaks, the authors used 26 microsatellite markers to test the relationships between outbreak flies caught in Adelaide in 2000 and 2002. Groupings between individuals were tested using both a model-based clustering method (implemented in the Structure program) and relatedness testing, using both simple exclusion tests and relatedness coefficients. While many flies appeared unrelated, one group of at least six full sibs was detected, all of which were trapped in the same month. Unexpectedly, these six flies were trapped at sites separated by distances greater than the unaided dispersal distance of Q-fly, implicating human-aided dispersal of infested fruit within Adelaide. Thus simultaneous trappings of flies separated by kilometres are not necessarily separate outbreaks as has been assumed. The implications for current outbreak control strategies are discussed.