Interactions between Heliothis zea (Boddie) and selected cotton cultivars

Abstract

Cotton bollworm interactions were studied on selected Upland cotton cultivars in 1981-83 at Corpus Christi, Texas. Neonatal bollworm, Heliothis zea (Boddie), larvae were confined on cotton plants for seven days in whole plant cages in 1981 and 1982. Measurements of plant damage, larval growth and survival in relation to relative tannin levels were used to investigate cotton resistance to bollworm. Tannin quality and concentration were found to have a positive association with resistance among the cotton cultivars. Cotton yield responses to discrete bollworm larval densities on the cotton cultivars, CAMD-E, SP-37, STV-213 and glandless RDC-102, at three phenological growth periods were determined in 1982 and 1983. Interactions were determined between bollworm larval density, square, and boll damage and lint yield for each cultivar. There were significant differences among cultivars for damaged squares at phenological growth stages of 1/3 grown square and second week of bloom. Data collected using STV-213 produced a lower regression slope for damage at the 1/3 grown square stage of growth than data collected from CAMD-E, SP-37 and RDC-102. However, at second week of bloom, low damage to CAMD-E indicated that it possessed a moderate level of resistance to bollworm compared with the other cultivars. There was no yield reduction on any cultivar when infestations were made 30 after first bloom. Differences in level of resistance among cultivars were attributed, in part, to an increase in quantity and quality of condensed tannins. Economic injury levels (EIL) were developed for the four cultivars at 1/3 grown square stage and second week of bloom stage of growth. EIL calculations were based on regression slope of percent damaged square to percent lint yield loss. Dynamic cost/benefit EIL tables were determined for each cultivar and growth stage, thus forming a series of EIL schedules for use in the Texas Coastal Bend region EIL's were lowest during the 1/3 grown square stage when all cultivars were most susceptible to damage. As plants matured, susceptibility to bollworms declined and EIL's increased for all cultivars.