Temporal and Spatial Genetic Variability of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois), Populations in a Small Geographic Area

Five populations of Lygus lineolaris (Palisot de Beauvois) were sampled from locations near Stoneville, MS, USA at three time points in May, July, and September 2006.  Genotype data obtained from 1418 insects using 13 microsatellite markers were analyzed using standard methods to obtain population genetic parameters such as inbreeding coefficients, gene flow, and linkage disequilibrium.  Analysis of molecular variance (AMOVA), Bayesian analysis, and factorial correspondence analysis (FCA) were carried out to evaluate the populations for genetic structure. The total number of alleles per locus across all populations ranged from 9 to 25 and the average allelic richness calculated by rarefaction across all loci ranged from 3.0 to 3.46.  The populations also had low Garza-Williamson indices (M values) ranging from 0.283±0.126 to 0.524±0.260, which indicated a bottleneck. Deviations from Hardy-Weinberg equilibrium (HWE) and linkage disequilibrium at some loci in some populations may have indicated selection at some loci.  Bayesian simulations using STRUCTURE software indicated the presence of two genetic clusters in all populations.  Populations collected in May 2006 had a high proportion of cluster 1 genotypes (except for the population B) and those collected in September had a high proportion of cluster 2 genotypes.  FCA analysis also separated the populations into two groups, one consisting of populations with predominantly genetic cluster 1 and another with predominantly genetic cluster 2 insects.  Hierarchical statistics (AMOVA) of population groupings based on collection time and genotype clusters produced the highest variance values (p<0.001). Considering the crops, especially cotton,  grown around the collection sites and the high number insecticides sprays applied  to cotton for controlling tarnished plant bugs in the 2005 and 2006 growing seasons, selection by insecticides was the most likely cause for the temporal variation in molecular structure observed in the L. lineolaris populations.