Effects of Insecticide Applications on Bemisia argentifolii (Homoptera: Aleyrodidae) Densities and Honeydew Production

Results of earlier studies designed to determine adult whitefly, Bemisia argentifolii Bellows & Perring, densities at which cotton, Gossypium hirsutum L., 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 3 dates, lint was collected and analyzed for sugars using high-performance liquid chromatography. Densities of adults per 5th mainstem leaf, adults per 10-s vacuum sample, and whitefly immature 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 drop 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. Amounts (micrograms) of trehalulose on top and bottom bolls were generally highest in the control treatment and lowest in the 5-adult treatment, but there were generally no significant differences among amounts from 5-, 10-, and 15-adult treatments. Honeydew drop densities were unexpectedly low in control and untreated plots on some later dates. Control and untreated plants also had fewer leaves than other plants during these times, suggesting leaf loss 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, by treating at the 10 threshold, fewer applications were needed. This would reduce the immediate costs to growers, and also would reduce long term problems associated with insecticide resistance.