Hybridization and introgression between Helicoverpa zea and H. armigera: an adaptational bridge

The invasion of organisms into new ecosystems is an increasingly common phenomenon due to the movement of commodities in global trade. One of the most complex scenarios post-invasion is when the invasive species resembles a native pest; even more so when they can hybridize and produce fertile progeny. The global pest Helicoverpa armigera had been detected in Brazil in 2013 and generated a wave of speculations about the possibility of hybridization with the native sister taxa Helicoverpa zea. In the present study, we used genome-wide SNPs genotyped in field-collected individuals to investigate hybridization between H. armigera and H. zea in different Brazilian agricultural landscapes. The results indicated that the frequency of hybridization varied from 15 to 30% depending on methods used. Mix ancestry between H. zea and H. armigera in hybrids (introgression) was around 10% in all tested methods. Hybridization also varied considerably depending on the geographic locations where the sample was collected, forming a ‘mosaic’ hybrid zone where introgression may be facilitated by environmental and landscape variables. Both landscape composition and bioclimatic variables point to the presence of maize and soybean as the main factors explaining the high percentage of introgression in agriculture landscapes. In addition, the impact of multiple H. armigera incursions is reflected in the structured and inbred pattern genetic diversity. Our data show that the landscape composition and bioclimatic variables influence in the introgression rate between H. armigera and H. zea in agricultural areas. The continuous monitoring of the hybridization process in the agricultural fields is necessary since agricultural expansion, climatic fluctuations, a changing composition of crop species and varieties, and dynamic planting seasons are some factors in South America that could promote a sudden alteration in the introgression rate between Helicoverpa spp. Introgression between invasive and native pests also can dramatically impact evolution on host ranges and resistance management.