Field observations of the cotton aphid, Aphis gossypii Glover, from 1999 to 2001 indicated an increase in percentage of winged aphids in cotton fields after an application of imidacloprid. Cotton aphid wing formation and fecundity of offspring were evaluated in a spray booth following five treatments: imidacloprid near LC50 concentration on cotton, dicrotophos near LC50 concentration on cotton, water spray on cotton, water spray on silk plants, imidacloprid spray near LC50 concentration on silk plants. Silk plants were used to differentiate topical and systemic effects of imidacloprid. Prior to spraying, 40 aphids were transferred onto each plant. Aphids were moved from the silk plants onto unsprayed cotton plants 3 h post-spray. Offspring from imidacloprid-treated aphids on cotton produced twice as many winged offspring (8%) as did aphids from other treatments (3% to 4%) and only one-third as many offspring per founding relative to aphids in other treatments. In addition to increasing emigration by winged aphids, an increase in the proportion of winged aphids among survivors of an imidacloprid treatment may further reduce the number of aphids in a treated field because winged aphids require a longer developmental time, produced fewer offspring, and have an increased risk of mortality.
