Cross-species amplification and intra and interpopulational polymorphism of microsatellite loci in Helicoverpa armigera and H. zea (Lepidoptera: Noctuidae) in Brazilian cropping systems

The Old World bollworm Helicoverpa armigera (Hübner) was recently discovered in Brazil. This species is closely related to the New World bollworm Helicoverpa zea (Boddie), and mating among species has already been reported under laboratory conditions. Here, we tested the cross-species amplification of twenty microsatellite (SSR) loci in field populations of H. armigera and H. zea collected from Brazilian cropping systems. Seven SSR loci were successfully amplified and polymorphic in both species except for the locus HaC14, which was monomorphic for H. zea. All SSR loci were in linkage equilibrium, and deviations from Hardy Weinberg Equilibrium were only observed for the locus HarSSR1 in HaRS-2 population, where null alleles were present. A moderate level of polymorphism was detected in H. armigera and H. zea populations with a mean number of 4.14 alleles, and 2.24, respectively. Interestingly, most of the populations of the recent invader H. armigera showed higher genetic diversity (Ho ˂ He) and inbreeding coefficients (f) than those in H. zea populations. The genetic identity of each species was recovered in the STRUCTURE analysis, where the populations formed two clusters (K = 2) according to their species. STRUCTURE also suggested the occurrence of potential hybrid offspring between H. armigera and H. zea individuals in natural conditions. These SSR loci will be valuable in characterizing population differentiation, invasion routes, adaptation, reproductive behaviour and intra- and interspecific gene flow in H. armigera and H. zea populations in Brazil, the USA, and other areas where these two pests occur.