Induction of cotton aphid outbreaks by insecticides in cotton
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During 1989 and 1990, field studies were conducted to determine effects of cypermethrin and sulprofos, which are used for control of Heliothis virescens and Helicoverpa zea in cotton, on outbreaks of cotton aphid, Aphis gossypii Glover. During 1989, cotton aphid outbreaks occurred in both insecticide-treated and untreated plots. However, aphid densities were greatest in the sulprofos-treated plots and lowest in the cypermethrin-treated plots, even though insecticide-induced aphid mortality could not be detected in either treatment. In 1990, sulprofos-treated plots contained the most aphids, but unlike 1989, the untreated plots had the fewest aphids. Rates of aphid parasitism by Lysiphlebus testaceipes (Cresson) were low in 1989 and 1990, and aphidopathogenic fungus infections were common only late in the season during 1990. Parasitism and fungal infections were most common in the sulprofos-treated plots, which contained the most aphids. Sulprofos-induced cotton aphid outbreaks could not be attributed entirely to the destruction of natural enemies. Late-season growth and fruiting patterns of the cotton plants indicated that sulprofos-treated plants continued active growth after the plants in the other treatments had begun to senesce. Furthermore, higher concentrations of the amino acid threonine and total essential amino acids were detected in the plant sap of sulprofos-treated cotton plants. Sulprofos may have contributed indirectly to aphid outbreaks by altering the biochemistry of the plant in a way that better suited the aphid's nutritional requirements, thus increasing aphid population growth. 1993.
