Genetic differentiation and reduced reproductive compatibility between Californian populations of bean thrips, Caliothrips fasciatus (Pergande) (Thysanoptera: Thripidae)

Bean thrips, Caliothrips fasciatus (Pergande), is a major quarantine issue for the export of fresh navel oranges from California, is highly polyphagous, and is widely distributed throughout California, being found in urban, agricultural, and natural areas. However, fundamental aspects of its biology and behaviour have received little research attention. Here we investigate the possibility that bean thrips is in fact a complex of cryptic species by quantifying genetic variation among Californian populations and by assessing the crossing compatibility of three geographically disparate populations. Variation in the mitochondrial COI gene was considerable, with 56 haplotypes detected from only 173 sequenced individuals, and the distribution of these haplotypes was highly structured. In the crossing compatibility assay, females paired with a male drawn from a population other than their own were significantly less likely to produce any offspring, and in those cases where they did, were significantly less fecund. This difference in fecundity resulted from a reduction in the number of female (but not male) offspring produced, indicative of a level of interpopulation gametic incompatibility in this haplodiploid system where only females are produced from a fertilized egg. Screening of the populations involved revealed that Wolbachia was not a factor in this incompatibility.