Hybridization Potential of Two Invasive Asian Longhorn Beetles

SIMPLE SUMMARY: Hybridization may occur within individuals of closely related species or species complexes that exhibit similar reproductive systems and behaviors and share overlapping distributions. Successful hybridization results in introgression of genes from one species to another and could significantly modify some essential traits of the hybrids. It is, therefore, important to consider hybridization potential especially among exotic invasive species, which may compromise the implementation of management programs. Asian longhorned beetle (ALB) and citrus longhorned beetle (CLB) are high-risk invasive pests worldwide, attacking various healthy hardwood trees. These two species share some similar host plants and overlapping distributions in large parts of their native ranges in China and the Korean peninsula as well as similar reproductive behaviors. Another longhorned beetle species occurs only in Japan but is considered as a synonym of CLB (JCLB). We found a Chinese CLB population did not cross successfully with a Chinese ALB population, but a JCLB population (male) crossed successfully with a Chinese ALB population (female) to produce viable eggs. We also found CLB crossed successfully with JCLB to produce fertile offspring. This raises potential concern that invasion of these currently isolated species or subspecies into the same regions may facilitate potential inter- or intra-specific hybridization. ABSTRACT: The Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky) and citrus longhorned beetle (CLB), Anoplophora chinensis (Förster) (both Coleoptera: Cerambycidae: Lamiinae), are high-risk invasive pests that attack various healthy hardwood trees. These two species share some similar host plants and overlapping distributions in large parts of their native ranges in China and the Korean peninsula as well as similar reproductive behaviors. The original Anoplophora malasiaca (Thomson) occurs in Japan and has been synonymized as CLB (hereafter referred to JCLB). In this study, a 30-min behavioral observation of paired adults, followed by a four-week exposure to host bolts, showed that ALB could not successfully cross with CLB. Mating was observed between female CLB and male ALB but not between female ALB and male CLB, no laid eggs hatched. JCLB males successfully crossed with ALB females to produce viable eggs although the overall percentage of hatched eggs was lower than those from conspecific mating pairs. However, ALB males could not successfully cross with JCLB females. CLB and JCLB mated and produced viable hybrid offspring and the hybrid F1 offspring eggs were fertile. These results suggest an asymmetrical hybridization between ALB and JCLB, and that both CLB and JCLB might be considered as two subspecies with different hybridization potential with congeneric ALB. Given their potential impacts on ecosystems and many economically important tree hosts, invasion of these geographically isolated species (ALB and JCLB) or distant subspecies (CLB and JCLB) into the same region may facilitate potential hybridization, which could be a potential concern for the management of these two globally important invasive forest pests. Further studies are needed to determine if fertile hybrid offspring are capable of breeding continually or backcrossing with parental offspring successfully.