Prostephanus truncatus outcompetes Sitophilus zeamais under varying temperatures and introduction sequence on stored maize grain

Coexistence of insect pests can result in facultative or antagonistic interactions. For sympatric pest species, explaining coexistence is crucial for understanding their combined impact, resource competition, and may inform management strategies. Prostephanus truncatus and Sitophilus zeamais commonly coexist as primary colonisers in stored maize grain. To determine how these species interact, two experiments mimicking competition scenarios on stored grain were conducted at 25, 30 and 35 °C (65 % RH). In Experiment 1, P. truncatus and S. zeamais were introduced simultaneously (interspecific) and in singular (intraspecific) populations at low (20), medium (40), and high (80) parental densities. In Experiment 2, we used similar temperatures and parental densities. However, one species was introduced 10 days after the other, and vice versa. Mini-polypropylene bags, each loaded with 65 ± 5g of dried orange maize grain, were used for both experiments. Progeny production, grain damage, grain weight loss, insect feeding dust and holes on bags bored by beetles, were recorded after 65 days of storage. Results showed that (i) P. truncatus outcompeted S. zeamais in interspecific interactions at 25 and 30 °C across parental densities, (ii) both species’ ecological performances were suppressed at 35 °C, (iii) P. truncatus caused higher grain damage regardless of the introduction sequence with S. zeamais and (iv) P. truncatus dispersed by tunnelling through polypropylene bags to avoid competition. Understanding interactions among sympatric pest species is essential for accurately predicting infestation outcomes and developing effective pest management under increasingly warming environments.