RELATIONSHIP BETWEEN AMBIENT AND LEAF-LITTER TEMPERATURES IN OVERWINTERING HABITATS OF BOLL-WEEVIL (COLEOPTERA, CURCULIONIDAE)

Temperature data are unavailable for most boil weevil overwintering ha bitats. As a result, ambient data often are used to estimate overwinte ring survival and emergence. In this study, relationship of ambient an d overwintering habitat temperatures was determined for 6 habitats in the Rolling Plains of Texas. The amplitude of the daily temperature cy cle in the leaf litter of each habitat was dampened compared with that recorded for ambient. Average minimum daily leaf litter temperature w as 3.19 degrees C higher in the shelterbelt habitat, followed by mesqu ite-grass pasture (3.54 degrees C), tall shinnery motte (3.64 degrees C), low shinnery brush (3.81 degrees C), lovegrass (4.01 degrees C), a nd pecan (6.01 degrees C). Likewise, the average maximum daily leaf li tter temperature was 3.77 degrees C lower in shelterbelt, followed by pecan (3.86 degrees C), lovegrass (3.87 degrees C), mesquite-grass pas ture (4.07 degrees C), low shinnery brush (5.51 degrees C), and tall s hinnery motte (6.12 degrees C). Stepwise multiple regression of hourly leaf litter temperatures explained 93% of the variability, with hourl y ambient temperature and week of year being significant variables. Si milarly, multiple regressions of daily leaf litter minimum temperature s and daily leaf litter maximum temperatures explained 96 and 90% of t he variability, respectively, with ambient temperatures and week of ye ar being significant variables for both regressions. The effect of tem perature quality (ambient versus leaf litter) and sampling frequency ( hourly versus daily) on positive (>6.1 degrees C) and negative (<0.0 d egrees C) degree-days experienced by overwintering boil weevils was qu antified for each of the 6 habitats for 4 yr of independent data, repr esenting 2 mild and 2 severe winters. Degree-day calculations based on fitting minimum-maximum data to an asymmetrical double sine curve ove restimated positive degree-day accumulation by 2.5%. Ambient temperatu re positive degree-days were similar to that for mesquite-grass pastur e habitat, but the ambient temperatures overestimated positive degree- days experienced by overwintering weevils in the pecan by 6.5%, follow ed by low shinnery brush (6.7%), lovegrass (8.7%), tall shinnery motte (9.2%), and shelterbelt (15.7%). All habitats had significantly fewer cumulative negative degree-days compared with that calculated for amb ient. Pecan leaf litter accumulated 99% fewer negative degree-days, fo llowed by shelterbelt (95%), tall shinnery motte (88%), low shinnery b rush (82%), lovegrass (71%), and mesquite-grass pasture (50%).