Honeydew contamination of cotton, Gossypium hirsutum L., lint by whiteflies, Bemisia argentifolii Bellows & Perring, is a major concern at textile mills and is well documented. Results of studies designed to determine adult whitefly densities at which cotton should be treated to reduce honeydew contamination have been variable. In this study, we determined the relationship between frequency of insecticide applications triggered by thresholds of 5, 10, 15, and 25 adult whiteflies per leaf and honeydew production by B. argentifolii feeding on cotton. Honeydew production was monitored on 15 dates from 21 May to 27 August 1996 in Brawley, CA, using water-sensitive papers placed on upper and lower leaves and bolls. On 4 dates lint was collected and analyzed for sugars using high performance liquid chromatography (HPLC). Whitefly densities and honeydew production were both affected by frequency of insecticide applications. Densities of adults per 5th mainstem leaf, adults per 10-s vacuum sample, 1st and 2nd instars, and 3rd and 4th instars per square centimeter of leaf were generally higher in control plots (1 insecticide application), plots treated at 25 adults (4 applications), and untreated plots than in plots treated at 5, 10, and 15 adults (11, 6, and 5 applications, respectively). In general, numbers of honeydew drops per square centimeter were higher in control, 25 adult, and untreated plots than in 5, 10, and 15 adult plots. Papers placed on uppermost bolls received more drops later in the season than did papers placed on the lowest bolls. Honeydew production was generally lowest throughout the season in the 5 adult treatment. However, it was not significantly different than the 10 or 15 adult treatments on 13, 20, and 27 August. There was no difference in honeydew drop diameters among treatments. Amounts of trehalulose did not differ among treatments on 23 July. However, amounts of trehalulose on top and bottom bolls were generally highest in control treatments and lowest in the 5 adult treatments on 6 and 20 August. There were generally no significant differences in the amounts from 5, 10, and 15 adult treatments. Honeydew drops per square centimeter were unexpectedly low in control and untreated plots on some later dates, especially on papers on bottom bolls. Coincidentally, control and untreated plants had fewer leaves than other plants during these times, with most of the lower, older leaves dropping off by August. This suggests leaf loss and plant level may account for some variability in honeydew production during late season. Seedcotton yields differed only between 10 and 25 adult threshold plots. At Brawley, CA, insecticide treatments at 5 and 10 adults per leaf seemed equally sufficient for reducing whitefly honeydew production. However, fewer applications were needed to maintain the 10 threshold, which would reduce the immediate costs to growers and also would reduce longer term problems associated with insecticide resistance.