Apparent selection of field-released genotypes of the biological control agent Tetramesa romana Walker

Genotype matching is a common filter used in the selection of biological control candidates.  However, the strength of this filter is often difficult to assess or evaluate post-release. The permitted release of  the parthenogenetic arundo wasp (Tetramesa romana Walker) on the clonal invasive giant reed presents a unique opportunity to effectively evaluate the field establishment of different genotypes and the importance of genotype matching. In October 2010, equal numbers (n=2000) of females of four different genotypes of the arundo wasp were field-released in six giant reed-infested sites along the southmost portion of the Rio Grande River. Three release sites were spaced 25 km apart near Del Rio, TX and the remainin three were 600 km south near Brownsville, TX.  Previous studies indicated no presence of the arundo wasp at these sites prior to release.  In each subsequent year after release, estimates were collected at each site on overall population abundance of the arundo wasp using sticky traps and timed counts.  Up to 50 individuals were collected at each site at each year and analyzed for genetic differences using microsatellites markers of simple sequence repeats (SSR).  At year one (2011), all four genotypes were present across all sites (but not necessarily within each site), with some differences in the relative abundance of each genotype, especially along the north-south gradient.  At year two (2012), one genotype was most commonly collected, especially in the southern sites, where it represented close to 90% of all individuals collected.   Overall differences in the relative genotype abundance across years, with one genotype dominating over time, indicate that there is either competition among genotypes or selective predation of certain wasp genotypes. Differences in both relative genotype abundance and overall population abundance among sites, especially between north and south sites, suggest that climate matching may play an important role in the relative success of different genotypes, and thus should be another consideration when selecting and rearing a biological control agent.