Pink Bollworm (Lepidoptera: Gelechiidae) Egg Hatch, Larval Success, and Pupal and Adult Survival on Okra- and Normal-leaf Cotton1

Abstract

Previous observations that okra-leaf cotton, Gossypium hirsutum L., sustained less seed damage caused by pink bollworm (PBW), Pectinophora gossypiella (Saunders), than normal-leaf cotton prompted a search for the cause of the reduced damage. In one series of experiments, bolls of ‘Stoneville 7A’ okra-leaf and ‘Stoneville 7A’ normal-leaf cotton were infested artificially with PBW eggs or first instars and boll temperatures were monitored. Egg mortality was not significantly different, but number of PBW entrance holes was reduced ca. 13% in bolls of okra-leaf cotton. Boll temperatures generally were slightly higher in okra-leaf cotton but differences were not great enough to explain the difference in number of entrance holes or insects per boll. In a second series of experiments, fourth instars were placed either in boxes of soil under plant canopies and collected later, or in containers placed in canopies where they were allowed to tunnel out of the containers, fall to the soil, and emerge as adults. In the soil boxes, no significant differences were found in temperature, relative humidity or in insect survival under the normal- and okra-leaf canopies. In the larval emergence experiment, soil temperature was significantly higher under the okra-leaf canopy than under the normal-leaf canopy but larval emergence from bolls and moth emergence from pupae were not significantly different.