Tracking an invader: the origin and genetic relationships of Asian citrus psyllid (Diaphorina citri) in California

In California, Asian citrus psyllid (ACP), Diaphorina citri Kuwayama – (Hemiptera: Psyllidae) was first detected in San Diego County near the Mexico border. Additional populations were subsequently discovered over 90 miles to the north in Orange and Los Angeles Counties. It is generally believed that California’s entire ACP population is the result of a northward expansion from Mexico to Los Angeles. However, the northward expansion hypothesis is not supported by the geographic distribution of ACP, in which large gaps exist between populations despite continuous habitat. This raises questions about the origin of ACP in California regarding the number of invasion events and the source populations of these invasions. We address these questions by examining genetic relationships between California populations and others worldwide. We investigated the relatedness of populations collected from ten countries using mitochondrial cytochrome oxidase I (mtCOI) haplotypes. Additional populations were investigated using data sourced from GenBank. Determining these genetic relationships makes it possible to identify the origin of ACP populations in California and potential routes of invasion.