Competition of three species of Sitophilus on rice and maize

Authors: ATHANASSIOU, CHRISTOS - University Of Thessaly; KAVALLIERATOS, NICKOLAS - Agricultural University Of Athens; Campbell, James - Jim

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2017
Publication Date: 3/6/2017
Citation: Athanassiou, C.G., Kavallieratos, N.G., Campbell, J.F. 2017. Competition of three species of Sitophilus on rice and maize. PLoS One. 12(3):e0173377. https://doi.org/10.1371/journal.pone.0173377.
DOI: https://doi.org/10.1371/journal.pone.0173377

Interpretive Summary: Stored grain such as wheat, rice and corn is often infested by multiple species of stored product pest insects, leading to situations where insects with similar strategies of grain exploitation compete for resources and this in turn can lead to localized coexistence or extinction of species. Laboratory tests examining potential competition among three closely related weevil pests of grain, the granary weevil, Sitophilus granarius, rice weevil, Sitophilus oryzae and maize weevil, Sitophilus zeamais, revealed that the species differed in the number of progeny they produced on both rice and corn. Regardless of the species combination, rice weevil had the highest numbers of adult progeny produced and maize weevil was intermediate, although in some comparisons these differences were not significant. Granary weevil numbers were very low on both rice and corn, suggesting little or no progeny production. For all weevil species, the numbers of adult progeny produced was considerably higher on rice than on corn, with the differences between the species also being much less on corn than on rice. This suggests that while the rice weevil is strongly favored to outcompete the other two species on rice, on corn the outcome would likely be less certain and take longer to be resolved. These findings highlight how intrinsic rates of increase can help predict the potential outcome of competition among these major pest species and perhaps explain the predominance of certain species in stored grain.

Technical Abstract: Laboratory tests were carried out in order to examine competition among three cogeneric species on rice and maize: the granary weevil, Sitophilus granarius, the rice weevil, Sitophilus oryzae and the maize weevil, Sitophilus zeamais. For this purpose, a total of 30 adults were placed in vials that contained 50 g or either rice or maize: 30 adults of S. granarius, 30 adults of S. oryzae, 30 adults of S. zeamais, 15 adults of S. granarius+15 adults of S. oryzae, 15 adults of S. granarius+15 adults of S. zeamais, 15 adults of S. oryzae +15 adults of S. zeamais, and 10 adults of S. granarius+10 adults of S. oryzae+10 adults of S. zeamais. After 62 days at 30oC and 70% relative humidity the number of individuals of each species were counted. Insect damaged kernels (IDK), weight of frass and grain weight were measured. When each species was alone, S. granarius had the lowest numbers of adults in both grains, which did not exceed 34 adults/vial, and S. oryzae numbers were always higher than other species. For S. oryzae and S. zeamais, the numbers of adults were considerably higher on rice than on maize. On rice, S. oryzae numbers ranged between 281 and 563 adults per vial, while for S. zeamais between 137 and 372 adults per vial. At the same time, for both species on maize, adult numbers did not exceed 54 adults per vial. The number of S. oryzae adults were constantly higher than the other species in all combinations tested. Moreover, for rice, IDK in the vials that contained S. oryzae, either alone or in combination with other species, was higher than all the other combinations. Similarly, grain weight was lower in the vials that contained S. oryzae compared to the other species combinations. In general, for S. oryzae and S. zeamais progeny production was increased with the increase of the number of the initial adults that had been placed inside the vials.