Two grain beetle species, one resource, different patterns of genetic structure: implications for management

Rhyzopertha dominica and Tribolium castaneum are key pests of stored grains globally. These two species often occur together in infestations, and are seldom found outside the agricultural environment. Understanding the movement of these beetle pests is crucial for the development of management strategies, in particular to prevent the spread of phosphine resistance, which is a serious issue in many countries. We sampled both of these beetle species from farm silos across Australia, and used microsatellite markers to assess whether these two pests sharing the same resource show similar patterns of genetic diversity and genetic structure. Both species had high levels of genetic diversity, and showed some evidence of genetic structure across Australia, but the patterns of genetic structure differed across the two species. Specifically, our results suggest that there is significant gene flow in T. castaneum across Australia, with the clear isolation-by-distance pattern indicating that active flight may play an important role in determining genetic structure in this species. The significant movement of T. castaneum beetles across Australia will likely result in the continued spread of phosphine resistance alleles across Australia, leading to increased incidence of strongly resistance populations. Less gene flow was evident in R. dominica, suggesting movement of these beetles among localities is more restricted. Our results demonstrate that pests mostly sharing the same resources can significantly differ in their genetic structure and genetic diversity, suggesting species-specific management practices are essential.