Predicting biological events in the life history of the pecan nut casebearer using a degree day model

Includes bibliographical references (leaves 164-175)A degree day model for predicting overwintering and 1st summer generation pecan nut casebearer (pnc), Acrobasis nuxvorella Neunzig (Lepidoptera: Pyralidae), activity was developed. The starting date and base temperature resulting in the most accurate predictions was determined at College Station, Texas using temperature records from Climatological Data (1918-1923) and field data from Bilsing (1926, 1927) in 1918-1923. Model predictions were compared to the mean calendar date of activity, the model using temperature records from hygrothermographs and the model using a sine curve modification. The model was verified at Shreveport, Louisiana and Brownwood, Texas using pnc black light trap catch data (Calcote, unpublished data). Start dates were observed to vary while base temperature exhibited little variation. An average number of 2.72 frost free days (ffd) were required for a 1 day change in the start day. The model was generalized using ffd and tested on data obtained from the literature. Results of application of the model on a real time basis were determined using start dates based on ffd and linearly interpolated temperature normals when actual daily temperature records were unobtainable. While several clusters had 2 eggs, they were seldom oviposited on the same nut. Oviposition occurred on the tip of the pistil and the calyx lobes only. Insufficient evidence was obtained to reject the null hypothesis that nut entry by the 1st summer generation pnc and physiological drop were independent. Nut entry occurred over ca. 1200 degree days at College Station, Texas in 1980 and 1981. The average number of nuts destroyed/cluster by the 1st summer generation pnc ranged from 1.72-2.55 and the average number of nuts undamaged/cluster ranged from 0.52-3.1. Significant differences in cluster size and nut position in relation to nut infestation were not obtained. The 1st summer generation pnc prefered to enter the proximal end of the nut adjacent to the peduncle. Overwintering generation male pnc moths emerged and were caught prior to females; however there was little difference due to sex. The observed sex ratio for overwintering generation pnc moths approximated a 1:1 ratio (males to females)