Comparison of insect injury-cotton yield response functions and economic injury levels for Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) in the lower Gulf Coast of Texas

Insect injury-crop yield response functions (i.e., regression equations) and economic injury levels (EILs) were developed and compared for the bollworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliothis virescens (F.), attacking cotton, Gossypium hirsutum (L.). Plant injury was sampled 7 d after plants were infested with neonates. Cotton cultivars used were 'Deltapine 50' and 'TAMCOT CD3H' at growth stages of one-third-grown flower bud (square), second week after initiation of anthesis (flowering), and 30 d after initiation of anthesis. Injury-yield regression equations were significantly different between insect species and cotton cultivars and among growth stages and combinations of cultivar, insect species, and growth stage. EILs ranged from 4 to 9% and 3 to 7% injured reproductive organs (i.e., flower buds and capsules [bolls]) at one-third-grown flower bud and second week after initiation of anthesis, respectively. Yield was not influenced by insect injury when cotton was infested 30 d after initiation of anthesis. Differences in EILs between insect species ranged from 0 to 1 and 3 to 5% injured reproductive organs on 'Deltapine 50' and 'TAMCOT CD3H', respectively. EILs as determined from analysis of variance (ANOVA) ranged from 12 to 32% injured reproductive organs. Regression analysis proved to be superior to ANOVA in calculating EILs that vary with market values and management costs