D. R. Rummel

Relationship between Aphis gossypii (Homoptera: Aphididae) and sticky lint in cotton.

Abstract The study was conducted in the northern Texas Rolling Plains in 1999 to define the relationship between number of cotton aphids, Aphis gossypii Glover, and resulting contamination of cotton lint by honeydew. Whole-plot treatments were three furrow irrigation management treatments: cotton grown without supplemental irrigation (dryland), irrigated cotton with last irrigation in mid August, and irrigated cotton with last irrigation in late August. Subplots within each irrigation treatment included an untreated check, a plot treated with lambda-cyhalothrin to stimulate aphid population increase, a plot treated with lambda-cyhalothrin followed by pymetrozine after aphids began to increase, and a plot treated with lambda-cyhalothrin followed by thiamethoxam after aphids began to increase. Cotton aphids were counted on leaves picked from the top and bottom half of the plant. Cotton lint was analyzed for contamination by glucose, fructose, sucrose, and melezitose secreted by cotton aphids, and percentage leaf moisture and nitrogen and leaf sucrose concentrations were determined. The manual sticky cotton thermodetector was used to determine degree of lint stickinesss. There was a significant relationship between thermodetector counts and melezitose contamination on lint, and a melezitose concentration of 90.9 μg/g of lint was associated with a thermodetector count of 10, the threshold for sticky lint problems in textile mills. An equation was developed to estimate melezitose concentration on lint as a function of average numbers of aphids per leaf and the interaction between percentage leaf moisture and nitrogen. The number of aphids per leaf associated with a melezitose concentration of 90.9 μg/g of lint ranged from 11.1 to 50.1, depending on percentage leaf moisture and nitrogen. The threshold for sticky lint problems occurred when aphid numbers ranged between 11.1 and 50.1 per leaf after bolls open.

A Model for Predicting Boll Weevil (Coleoptera: Curculionidae) Overwintering Survivorship

Abstract Boll weevil, Anthonomus grandis grandis Boheman, overwintering survivorship was quantified monthly throughout the overwintering period (October to May) in Texas High Plains and Rolling Plains for 12 yr. A negative exponential model was developed to dynamically predict survivorship throughout the overwintering months. Survivorship was modeled as a function of the number of days that weevils were in the habitat, negative degree-days (<0.0°C), positive degree-days (>6.1°C), rainfall, and mortality during the first month of overwintering. First month mortality was modeled as a function of overwintering survival potential of weevils determined by dissection examination of their body lipid content and gonad atrophy. A nonlinear iterative multiple regression analysis showed that the model explained 94% of the variability in parameterization-verification data; a goodness-of-fit test showed that 97% of the estimated survival values did not significantly depart from their corresponding observed values. With independent validation data, 94% of the variability was explained by the survival model; a goodness-of-fit test for validation data showed that 96% of the predicted survival values did not significantly depart from their corresponding observed values. This model offers a greater understanding of boll weevil overwintering biology as it demonstrates a link between biological and climatic parameters. The model can be used to forecast weevil survivorship throughout the overwintering period in the Texas Plains.