Impact of Insect Management on Population Dynamics and Insecticide Resistance of Tarnished Plant Bug (Hemiptera: Miridae)

While transgenic plants targeting lepidopteran and coleopteran insects have been available for almost 20 yr, there are no transgenic crops that target hemipteran insects such as tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), though at least one company lists potential products in advanced stages of development. A resistance management model for the U.S. Mid-South was developed to aid in resistance risk assessments for transgenic crops targeting L. lineolaris , and validated against the prior case of pyrethroid resistance in this insect. The model predicted that resistance to a pyrethroid would evolve in 17.6–21.0 yr (depending on the initial resistance allele frequency), which was close to the 15–20 years observed in the field. Due to uncertainty in female fecundity, we varied fecundity from 3 eggs/female/day to 12 eggs/female/day. Sprays were applied based on action thresholds, and increasing fecundity therefore increased the number of sprays applied per year and decreased durability. We also varied the action threshold in cotton ( Gossypium hirsutum L.) fields (the population levels at which sprays were applied) from 17,600/ha to as low as 1,100/ha. Lowering the threshold increased the number of sprays applied, but also increased durability of the pesticide. Removing the noncotton host refuge present at the same time as cotton changed the relationship so that increasing the action threshold increased durability. The impact of insect resistance management on action threshold cost estimates will vary depending on the landscape, and cannot be assumed to always move the economic injury level in the same direction.