Preference, survival, and fitness of the invasive larger grain borer Prostephanus truncatus (Horn) on acorns of three native oak species

The larger grain borer Prostephanus truncatus (Horn) is an invasive insect pest on stored grains but can also exploit non-grain food sources. Currently this species has a limited US distribution but with climate change is predicted to expand further into the US. Alternative non-grain foods could play a role in range expansion and previous research has shown that acorns can be a suitable food for the lesser grain borer Rhyzopertha dominica (Fab.), a related species that is also a grain pest. We conducted P. truncatus preference assays with maize (Zea mays) and acorns from three different oak species: bur oak (Quercus macrocarpa), black oak (Quercus velutina), and red oak (Quercus rubra) and measured attraction, feeding damage, survival, and reproduction. Results demonstrated P. truncatus responded to volatiles of each acorn species, but responses were strongest to acorns from bur oak. Interestingly, volatiles from bur oak acorns were also significantly more attractive to P. truncatus than maize kernels. Bioassays showed that P. truncatus survival was poor on undamaged acorns, with 4% of individuals surviving after two weeks, but increased to 39% on damaged bur oak acorns. Bur oak was also the only acorn species tested in which viable progeny were detected. Further studies are currently underway to identify volatiles from bur oak acorn that may be attractive to P. truncatus. These findings suggest that P. truncatus populations possess the evolutionary plasticity to survive on acorns when grain is absent, alluding to heightened landscape risk for this invasive pest in the US.