Seasonal flight activity and associated frequency of rph2 phosphine resistance allele in Rhyzopertha dominica at bulk storage facilities in southern Queensland, Australia

Traps baited with aggregation pheromone lures for the lesser grain borer, Rhyzopertha dominica (F.) were deployed at two bulk grain storage facilities in southern Queensland, Australia from January 2018 to March 2019. This trapping provided data on flight activity in this species as well as sample specimens for screening for the strong phosphine resistance allele (K142E) of the rph2 gene. This species is a major pest in Australia where phosphine is the commonly used means of disinfesting stored cereal grains. Therefore, information on infestation pressure from flying beetles and the frequency of resistance genes in these beetles may provide a basis for improved pest and resistance management. Rhyzopertha dominica beetles were trapped at both depots throughout the study, with totals of 3699 and 6683 trapped at the two depots, respectively. Trap catch tended to fluctuate in synchrony at the two depots, with the lowest number caught during winter. There was a total of 15 trapping events during the study and the rph2 allele (K142E) was detected in 14 of them. The overall resistance allele frequency was estimated to be 7.4%, and this variant was present in 12.6% of screened beetles from each site, with most of them being heterozygotes (rph2^rs). This study shows that there was a great deal of similarity between the two sites, in relation to flight activity and frequency of rph2 alleles (K142E). It also shows the potential for using pheromone trapping as a passive means of collecting R. dominica beetles for monitoring the frequency of phosphine resistance alleles in a typical grain storage environment.