Environmental Stress Impacts on Egg Hatch and Larval Survival of Cotton Bollworm

Abstract

Cotton bollworm, Helicoverpa zea (Boddie), development under environmental stress was evaluated in laboratory and field trials in southern New Mexico. Constant exposure to 35°C and 17% relative humidity in the laboratory resulted in only 4% egg hatch. Stressed by high temperature, 35°C, or low relative humidity, 17%, alone, hatch rates were comparable to eggs held at 26°C and 50% relative humidity. Larvae maintained at 35°C and 17% relative humidity had only 9% survival. Cumulative mortality under these most stressful conditions was 99.64% from egg to pupation. Larvae exposed to only one stress (35°C or 17% relative humidity) had similar survival to pupation, 29 to 32%, less than half the 67% survival at 26°C and 50% RH. Field trials tested the effects of row orientation and row spacing on H. zea hatching rates. Hatch rates in row orientation trials ranged from 37 to 79%, with only one significant difference in east‐west vs. north‐south oriented rows in two years. Row spacing had no impact on H. zea egg hatch. Hatch rates ranged from 43 to 71% with no significant difference among row spacings 17, 34, 68, and 96 cm. Bollworm is very susceptible to environmental stress. However, bollworm develops in the plant canopy where it is generally not significantly impacted by differences in row orientation or row spacing.