Competition between Prostephanus truncatus and Sitophilus oryzae on maize: the species that gets there first matters

Laboratory tests were carried out in order to examine the population growth of Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on maize. These two species were placed either simultaneously or one species was allowed to colonize the kernels 7 days earlier than the other, at two temperatures, 26 and 30 °C for 65 days. Apart from progeny production, grain quality parameters, such as insect-damaged kernels (IDK) and undamaged kernels (NDK), the weight of frass and kernel weight were measured. Our data confirms that temperature plays a key role in the competition of these two species; P. truncatus seems to perform better at the higher temperature (30 °C), regardless of the presence of an additional species. Moreover, the results of the present study demonstrates that P. truncatus outcompetes S. oryzae. Sitophilus oryzae produced fewer progeny than P. truncatus in all combinations. Given the outcome of a competition, we hypothesize that most of the kernel damage was due to feeding by P. truncatus. Based on these data, we surmise that P. truncatus has a competitive advantage as an invasive species in new areas with stored maize, even in the presence of S. oryzae.