INTERRELATIONSHIPS BETWEEN BENEFICIAL ARTHROPODS AND HELIOTHIS VIRESCENS (F.) ON COTTON IN THE IMPERIAL VALLEY, INCLUDING DOSAGE-MORTALITY STUDIES ON H. VIRESCENS AND GEOCORIS PUNCTIPES (SAY)

The tobacco budworm, Heliothis virescens (F.), is primarily a late season pest of cotton in the Imperial Valley of California. Insecticides used early in the season against key pests such as the pink bollworm, Pectinophora gossypiella Saund., reduces populations of natural enemies, resulting in outbreaks of other pests such as Heliothis spp.; An evaluation of the interrelationships between beneficial arthropods and tobacco budworm populations in a cotton ecosystem was undertaken in 1978 and 1979. Four plots, 150 feet long and 12 rows wide, were paired to compare treated and untreated cotton. The whole plant bag sampling method was used to estimate arthropod populations.; The results indicated that two definite periods of insect abundance occurred in both years. These periods corresponded to square formation in the cotton plant. The most abundant insect pest populations in both years were thrips. They were highly correlated to Orius populations. Orius spp. were more correlated to immature thrips than to adults, indicating a preference for the immature stages. There was no significant difference for thrips, between treated and untreated plots in both years.; The tobacco budworm increased in numbers late in the growing season in both years. This increase corresponded with the decline in beneficial insect populations. High correlations were found between Orius, total predators, and Heliothis eggs. Heliothis larvae were not correlated to any of the beneficial species evaluated. Square formation was correlated to eggs but not to Heliothis larvae. Beneficial insect populations were higher late in the 1979 growing season as compared to that in 1978. The difference in populations was reflected in the number of Heliothis eggs present in both years. Fewer eggs were found in 1979.; A significant difference in populations between treated and untreated plots was obtained for some of the beneficial species, primarily the immature stages. These results probably were influenced by the mobility of the adult stage and the small size of the plots. Nevertheless, predators occurred in higher numbers in the untreated plots and remained longer therein than in the treated plots.; Dosage-mortality studies on the tobacco budworm showed an increase in the LD(,50) values from 1979 through 1981. Levels of resistance to the pyrethroids, permethrin and fenvalerate, increased 51x and 29x respectively, in the three-year period of evaluations (1979-1981). Methyl parathion LD(,50) values increased by 18x. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI...