Host-associated differentiation (HAD) is the presence of genetically divergent, host-associated populations. HAD has been proposed as a mechanism promoting adaptive radiation of host-associated lineages resulting over time in increased species diversity. Reports of HAD in phytophagous insects are mostly limited to the specialist, univoltine species in feral ecosystems or generalist, multivoltine, parthenogens in agricultural systems. Here we report presence of HAD in a generalist, mutlivoltine, non-parthenogentic insect herbivore in an agro-ecosystem. Cotton fleahopper, Pseudatomoscelis seriatus Reuter (Hemiptera: Miridae) is a generalist herbivore insect, which uses more than 120 host plant species besides cultivated cotton in North America. We studied this insect on two of its most preferred, native and uncultivated host plant species: horsemint (Monarda punctata) and woolly croton (Croton capitatus); and on cotton (Gossypium hirsutum), an introduced and cultivated host plant. Previous studies and field observations indicated that P. seriatus prefers native, wild hosts over cotton. In this study we used AFLP markers to examine the genetic differentiation of host-associated populations of P. seriatus in five locations, which are representative of distinct eco-zones within Texas.

Results/Conclusions

An overall F_ST = 0.10 indicates moderate genetic differentiation among P. seriatus populations. We found a geographic pattern of genetic differentiation among the host-associated populations of P. seriatus. In three locations two distinct genotypes of P. seriatus were found in association with horsemint and cotton/woolly croton, whereas in two different locations populations associated with cotton, horsemint and woolly croton were panmictic. In addition, a unique genotype associated with the three host plant species studied was found in one of the panmictic populations. The geographic pattern of host-associated differentiation corresponds to a precipitation gradient among the study locations. We suggest that precipitation differences translate into heterogeneity in vegetation composition, distribution of host plant species, and allochrony among host plant phenologies, which in combinations may generate the observed pattern of genetic differentiation among host-associated populations of P. seriatus.