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 .