Bradley Hopkins
Major Professor: Dr. Patricia Pietrantonio
Ph.D. Candidate
"Pyrethroid Insecticide Resistance in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)."
Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), commonly referred to as the cotton bollworm and corn earworm, is a polyphagous pest of multiple crops including cotton, corn, grain sorghum, soybeans, and tomatoes. One of the most common and inexpensive insecticidal control measures for this pest is the use of pyrethroid insecticides. Over the last five years, the Texas A&M University Insect Toxicology Laboratory has monitored H. zea resistance to cypermethrin across the state of Texas using the Adult Vial Test (AVT) that exposes pheromone trap-collected adult male moths to different concentrations of cypermethrin residues coated on the inside of 20 ml glass vials. The overall objective of this research was to determine if the current method of resistance monitoring is an accurate predictor of resistance in larvae and ultimately field failure of pyrethroids. Additionally, results show indirect evidence of the mechanisms responsible for resistance in this insect (e.g. target site, metabolic). LC50 and LC90 values and resistance ratios were determined for a susceptible H. zea colony, a resistant H. zea colony that has been selected in the laboratory with cypermethrin, and the Fl generation oflarvae collected from a Nueces Co. grain sorghum field in June 2007, by the following methods: neonate vial assay, third instar vial assay, adult vial assay, neonate leaf dip assay, third instar leafdip assay. Results of these experiments and implications are discussed.