Temperature-mediated competition between the invasive larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae) and the cosmopolitan maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae)

Authors: QUELLHORST, HANNAH - Kansas State University; ATHANASSIOU, CHRISTOS - University Of Thessaly; Bruce, Alexander; Scully, Erin; Morrison, William - Rob

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2019
Publication Date: 2/1/2020
Citation: Quellhorst, H., Athanassiou, C.G., Bruce, A.I., Scully, E.D., Morrison III, W.R. 2020. Temperature-mediated competition between the invasive larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae) and the cosmopolitan maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae). Environmental Entomology. 49(1):255-264. https://doi.org/10.1093/ee/nvz151.
DOI: https://doi.org/10.1093/ee/nvz151

Interpretive Summary: The larger grain borer and the maize weevil are important pests of stored corn in much of the world, the larger grain borer is an invasive species that mostly occupies tropical and semi-tropical areas of the world, while the maize weevil is more cosmopolitan, occurring in the same locations as the larger grain borer as well as more temperate regions. Since they both feed on corn, in areas where they overlap competition can occur and as species' ranges shift with changing climate, the larger grain borer may disperse and establish in new locations occupied by maize weevil. The competition between these two species may have significant implications for range expansion and the preservation of grain quality. When evaluating results of competition between these two species at different temperatures, ranging from 20 to 35 degrees Celsius, it was found that both species could co-exist, but that the larger grain borer was a superior competitor at higher temperatures, and maize weevil was more successful at moderate temperatures. When both species were present, most of the damage to the corn was due to the invasive larger grain borer not the maize weevil. Mold growth on the corn was greater when both species were present than when either species was alone, and the most abundant mold species was one that produces aflatoxin. Our results suggest that the postharvest management of insect pests may have to adapt in the future, and that increased grain damage might be possible with the spread and establishment of the larger grain borer.

Technical Abstract: Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), the larger grain borer, is endemic to Central America, but invaded Africa with disastrous consequences for maize production. Its main competitor is Sitophilus zeamais Motschulsky (Coleoptera: Cucurlionidae), the maize weevil, which has a more cosmopolitan distribution. These insect co-occur in many regions of the world and both are threats to stored maize. However, the impact of competition between these two species is not well understood as well as how competition affects grain quality and impacts the potential for P. truncatus to invade new areas under climate change. The aims of our study were to evaluate the outcome of interspecific competition between P. truncatus and S. zeamais at different temperatures on a fixed quantity of grain, and determine the effects on progeny production, grain damage, and mold growth. We found that coexistence may be possible at a range of 25–30 degrees Celsius, but mixed colonies experienced a direct competitive cost compared to colonies containing only conspecifics. The majority of the grain damage was the result of P. truncatus activity, but not S. zeamais activity. Finally, mold growth was greater where both species were present, and species of mold that produce aflatoxin were identified as being present. These results suggest that as there are an increasing number of areas where both species co-occur, P. truncatus will be capable of destroying much more maize in a shorter period compared to S. zeamais at temperatures greater than 25°C.