The effect of plant water stress on beneficial and pest insects including the pink bollworm and the sweetpotato whitefly in two short-season cultivars of cotton

The numbers of beneficial and pest insects were studied in 0.2-ha plots of Deltapine 50 (DP-50) and Stoneville 506 (ST-506), cultivars of upland cotton, Gossypium hirsutum L., irrigated weekly or biweekly at Maricopa, AZ. Plant water stress, as measured by leaf water potential, was 13% greater at 13 days than at 7 days in plants irrigated biweekly. Numbers of Lygus hesperus Knight were greater in DP-50 than in ST-506 and Nabis alternatus Parshley were greater in weekly- than biweekly-irrigated plots. Plants of DP-50 had 46% more pink bollworm, Pectinophora gossypiella (Saunders), larvae in bolls at the end of the season than did ST-506. Plants irrigated weekly had 32% more pink bollworm larvae than plants irrigated biweekly. Leaves of ST-506 averaged 35% more eggs of the sweetpotato whitefly, Bemisia tabaci (Gennadius), per gram of leaf tissue than leaves of DP-50. Leaves of plants irrigated biweekly had 27% more eggs and 35% more nymphs per gram than plants irrigated weekly. Samples of lint from the two cultivars irrigated biweekly had 46% more reducing sugar than lint from the cultivars irrigated weekly. Results indicate that numbers of immature sweetpotato whitefly on cotton plants can be reduced by 47% and similarly the percentage of sugar in the lint by selecting a less susceptible cultivar and reducing plant water stress.