Mn. Parajulee et al., RELATIONSHIP BETWEEN AMBIENT AND LEAF-LITTER TEMPERATURES IN OVERWINTERING HABITATS OF BOLL-WEEVIL (COLEOPTERA, CURCULIONIDAE), Environmental entomology, 26(2), 1997, pp. 135-141
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%).