Range expansion by avocado lace bug, Pseudacysta perseae (Hemiptera: Tingidae): a reassessment of population genetic structure reveals evidence for a second invasion into California

Pseudacysta perseae (Heidemann 1908) (Hemiptera: Tingidae), a foliar pest of avocados, was first discovered in urban San Diego County, California U.S. in 2004. In 2017, damaging populations of P. perseae were discovered in commercial Hass avocado groves in San Diego and Riverside Counties. The unexpected and rapid spread of P. perseae raised the question of whether this range expansion was an extension of the original incursion or the result of a second invasion event. Using sequences of the mitochondrial COI gene, we found strong evidence that P. perseae populations in southern San Diego County are comprised almost entirely of the single haplotype (A) that was detected in 2004. In contrast, newly established (2017 onwards) populations of P. perseae infesting commercial orchards consisted exclusively of a second mitochondrial haplotype (G). This haplotype is found in Florida and the Caribbean and is conclusive evidence that California has been invaded a second time. Molecular analyses also confirmed that invasive P. perseae populations in Hawai'i are haplotype G, indicating that California and Hawai'i populations may have originated from the same source area (possibly Florida), or that California may have acted as an invasion bridgehead for the invasion of Hawai'i. Reproductive compatibility of the primary (haplotype A) and secondary (haplotype G) invasive populations in California was confirmed via a series of reciprocal laboratory crosses and results suggest that fertility of hybrid eggs is increased. The potential consequences of this second invasion into California by P. perseae are discussed.