Predicted range expansion of the larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae), under projected climate change scenarios

Authors: HARMAN, RACHEL - Oak Ridge Institute For Science And Education (ORISE); Morrison, William - Rob; Ludwick, Dalton; Gerken, Alison

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2024
Publication Date: 5/16/2024
Citation: Harman, R.R., Morrison III, W.R., Ludwick, D.C., Gerken, A.R. 2024. Predicted range expansion of the larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae), under projected climate change scenarios. Journal of Economic Entomology. 117(4) 1686-1700. https://doi.org/10.1093/jee/toae085.
DOI: https://doi.org/10.1093/jee/toae085

Interpretive Summary: Larger grain borer is a destructive stored product pest native to South America that caused substantial post-harvest losses to maize after it was introduced to Africa in the 1980s and 1990s. Although not currently established in the US or Europe, climate change has the potential to shift or expand its range. To address this, we used occurrence data from its native range in Central America and its invasive range in Africa to predict where it could live under current climate conditions as well as where it could survive in 2050 and 2070 under several different climate change scenarios. The different levels of climate change, called Representative Concentration Pathways, were used to estimate how different climate extremes could impact species distribution larger grain borer over time. We found that temperature and precipitation most strongly influence current and future distribution, with areas of low temperature and/or high precipitation being least likely to be suitable for survival. With this in mind, we found that areas along coastal and equatorial regions were highly suitable for establishment and that areas of high suitability for larger grain borer survival would expand from 7 to 19% under the most extreme climate change model. Finally, the mean center of the native range in Central America is projected to move northward closer to the southern border of the US under two climate change scenarios, making it more likely this insect could establish here. Globally, this critically represents a range expansion, and not a range shift, as larger grain borer is predicted to occur in more geographic regions. These results can be used to identify areas that are most at-risk for establishment of larger grain borer, which can be used to increase surveillance and reduce the likelihood of establishment.

Technical Abstract: The larger grain borer (Prostephanus truncatus [Horn] [Coleoptera: Bostrichidae]) is a Central American native, wood-boring insect that has adapted to stored maize and cassava. In the late 1970s, P. truncatus was accidentally introduced to Tanzania and became a pest across central Africa. Unlike many grain pests, P. truncatus populations can establish and move within forested habitats. Consequently, novel infestations can occur without human influence. The objectives of our study were to (1) develop an updated current suitability projection for P. truncatus (2) assess the pest’s potential future distribution under different climate change scenarios, and (3) identify climate variables that best inform the distribution model. We used the WALLACE platform and the species distribution model MaxEnt to predict potential global distribution using bioclimatic variables and occurrence records. Future models were projected to 2050 and 2070 with Representative Concentration Pathways (RCP) 2.6 and 8.5. Prostephanus truncatus distribution was most limited by high precipitation and cold temperatures. Globally, highly suitable areas (>75%) primarily occurred along coastal and equatorial regions and totaled 7% under current conditions. Highly suitable areas at RCP 2.6 and 8.5 are estimated to increase to 12 and 15%, respectively, by 2050 and increase to 19% in 2070 under RCP 8.5. Centroids of highly suitable areas show the distribution centers move more inshore and away from the equator. Notably, the result is a range expansion, not shift. These results can be used to decrease biosecurity risks through more spatially explicit and timely surveillance programs for targeting the exclusion of this pest.