EFFECTS OF INSECTICIDE APPLICATIONS ON BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE) DENSITIES AND HONEYDEW PRODUCTION

Results of earlier studies designed to determine adult whitefly, Bemis ia argentifolii Bellows & Per ring, densities at which cotton, Gossypi um hirsutum L., should be treated to reduce honeydew contamination hav e been variable. In this study. we determined the relationship between frequency of insecticide applications triggered by thresholds of 5, 1 0, 15, and 25 adult whiteflies per leaf and honeydew production Lv B. argentifolii feeding on cotton. Honeydew production was monitored on 1 5 dates from 21 May to 27 August 1996 in Brawley. CA, using water-sens itive papers placed on upper and lower leaves and bells. On 3 dates, l int was collected and analyzed for sugars using high-performance liqui d chromatography. Densities of adults per 5th mainstem leaf, adults pe r 10-s vacuum sample, and whitefly immature instars per square centime ter of leaf were generally higher in control plots (1 insecticide appl ication), plots treated at 25 adults (4 applications): and untreated p lots Il lan in plots treated at 5, 10, and 15 adults (11, 6, and 5 app lications, respectively). In general, numbers of honeydew drops per sq uare centimeter were higher in control, 25-adult, and untreated plots than in 5-, 10-, and 15-adult plots. Papers placed on uppermost boils received more drops later in the season than did papers placed on the lowest boils. Honeydew drop production was generally lowest throughout the season in the 5-adult treatment. However, it was not significantl y different than the 10- or 15-adult treatments on 13, 20, and 27 Augu st, Amounts (micrograms) of trehalulose on top and bottom bolls were g enerally highest in the control treatment and lowest in the 5-adult tr eatment, but there were generally no significant differences among amo unts from 5-, 10-, and Ig-adult treatments, Honeydew drop densities we re 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 variabi lity in honeydew production during late season. Seedcotton yields diff ered only between 10- and 25-adult threshold plots. At Brawley, CA, in secticide treatments at 5 and 10 adults per leaf seemed equally suffic ient for reducing whitefly honeydew production. However. by treating a t the 10 threshold, fewer applications sere needed. This would reduce the immediate costs to growers, and also would reduce long term proble ms associated with insecticide resistance.