Monitoring for Pyrethroid Resistance in Bollworm (Helicoverpa zea) Populations in Texas and Tamaulipas, Mexico - 2008

A monitoring program evaluated the susceptibility of male bollworm, Helicoverpa zea (Boddie), populations to the pyrethroid insecticide cypermethrin using the adult vial test.  Moths were trapped near cotton fields using a synthetic pheromone trap and glass vials coated with different concentrations of cypermethrin dissolved in acetone were used to assess moth mortality.  Twelve Texas counties were surveyed, along with one location in Tamaulipas, Mexico, from March to September in 2008.  Data were collected from all collaborators and sent to the Insect Toxicology Laboratory (AgriLIFE Research) for analyses of LC₅₀ and LC₉₀ resistance ratios, followed by likelihood ratio tests of equality and parallelism. Uvalde, Nueces, and Williamson Co. populations exhibited the highest LC₅₀ resistant ratios: 8.4, 6.8, and 6.4, respectively.  These three populations, along with those of Burleson Co. and Tamaulipas, Mexico, were significantly more resistant than the susceptible population based upon likelihood ratio tests for equality.  Generally, populations monitored across other counties maintained susceptibility, and overall resistance levels for the state of Texas were lower in 2008 than in the previous several seasons.