Interspecific Mating Is Trivial and Asymmetrical Between Two Destructive Anoplophora Beetles

The Asian longhorn beetle (ALB), <i>Anoplophora glabripennis</i>, and citrus longhorn beetle (CLB), <i>Anoplophora chinensis</i>, are two destructive invasive wood-boring pests, with high similarities in morphology, geographical distribution, host range, life cycle, adult behaviors and male-produced pheromone, implying a potential existence of interspecific interactions. Matings have been found to occur across females and males of the two species when manually paired in confined spaces. However, interspecific mating and its regulating factors are unclear between sympatric populations on hosts. Herein, by observing mountings and tracking the beetles that freely coexisted on host branches in cages, we found that the majority of mountings appeared within species; however, interspecific mountings occasionally occurred between male CLBs and female ALBs. The CLB was more active than the ALB at night. It seems that males actively searched for female ALBs, while the inverse was the case with CLBs. The main release periods of shared pheromone components overlapped between the two species, while compound ratios had significant differences. Our results unveil a trivial and asymmetrical interspecific mating between ALBs and CLBs, implying a risk of co-outbreaks of the two species in either native or invaded areas.