Development of the First Cytochrome Oxidase I Barcode and Evidence for a Dominant Variant Associated with the Recent United States Invasion of the Pasture Mealybug Heliococcus summervillei (Hemiptera: Pseudococcidae) Complex

The Heliococcus summervillei complex is an emerging invasive mealybug that causes severe dieback in grasses in pastures and turfgrass landscapes. It is widespread in Australia and has recently been detected across the Caribbean, Mexico, and the United States. Accurate mealybug identification is challenging because of cryptic and overlapping diagnostic characters and limited taxonomic expertise and literature, making molecular tools essential for regulatory diagnostics and management. We developed the first Cytochrome Oxidase I (COI) sequences for morphology-based Type A and Type B variants of the H. summervillei complex using the Jerry–Pat mid-COI fragment and used them to examine mitochondrial variation across available populations. COI sequences reveal approximately 10% mitochondrial split between the Type A and Type B variants. Phylogenetic, haplotype network, and genetic distance analyses show that all Type B populations share a single mitochondrial haplotype, consistent with a single dominant maternal lineage associated with a recent pasture mealybug invasion of the United States and Australia. Type A in Barbados contains two closely related haplotypes that may represent a historically stable mitochondrial variant corresponding to the holotype’s morphological description of H. summervillei, based on morphology. Together, these results establish the first COI reference library for the H. summervillei complex, resolve mitochondrial lineage structure, and provide a practical tool for rapid identification and timely regulatory and pest management responses.