Wolbachia is gaining recognition as an environmentally friendly biocontrol agent because it can potentially exploit cytoplasmic incompatibility (CI) to suppress or replace populations of insect pests. Although large-scale applications have successfully controlled epidemic mosquitoes, progress with agricultural pests has been slower due to biological constraints. These constraints include difficulties in establishing stable infections and achieving effective CI between the introduced and wild populations.

Reciprocal CI - mutual incompatibility between hosts carrying different Wolbachia strains - has long been considered theoretically possible, but empirical examples are still uncommon, especially in agricultural pests. Unstable infections or haplodiploid reproduction can further limit the effectiveness of CI-based strategies in these pests. Despite the economic importance of many coleopteran pests, Wolbachia transinfection studies in beetles remain limited. Here, we report an interspecific Wolbachia transfer experiment in a stored-product pest beetle system. We introduced a Wolbachia strain from Callosobruchus analis into C. chinensis, a closely related species that naturally harbors CI-inducing Wolbachia. We then quantified reproductive compatibility between transinfected and naive host lines using reciprocal crossing experiments.

Consistent with theoretical predictions, but rarely observed empirically, interspecific transfer resulted in strong reciprocal incompatibility between the introduced and resident strains. Host genetic background remained an important determinant of CI expression; in the naive host, this genetic effect was accompanied by a stronger association between CI strength and Wolbachia density. Furthermore, CI induced by the introduced Wolbachia strain was rescued by one of the resident strains, suggesting functional similarity between their CI systems. But the evolutionary origin of this compatibility remains unclear. Taken together, these results demonstrate that reciprocal CI can arise following interspecific transfer in an agricultural pest and that host genetic background continues to influence CI expression after transfer. This system provides a novel empirical framework for studying host–Wolbachia coadaptation and highlights both the opportunities and limitations of extending Wolbachia-based biocontrol strategies to agricultural pests.