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 equation s) and economic injury levels (EILs) were developed and compared for t he bollworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliot his virescens (F.), attacking cotton, Gossypium hirsutum (L.). Plant i njury was sampled 7 d after plants were infested with neonates. Cotton cultivars used were 'Deltapine 50' and 'TAMCOT CD3H' at growth stages on 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 insec t species and cotton cultivars and among growth stages and combination s 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 cap sules [bolls]) at one-third-grown flower bud and second week after ini tiation of anthesis, respectively. Yield was not influenced by insect injury when cotton was infected 30 d after initiation of anthesis. Dif ferences in EILs between insect species ranged from 0 to 1 and 3 to 5% injured reproductive organs on 'Deltapine 50' and 'TAMCOT CD3H', resp ectively. 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 val ues and management costs.