Relationship Between Ambient and Leaf Litter Temperatures in Overwintering Habitats of Boll Weevil (Coleoptera: Curculionidae)

Abstract

Temperature data are unavailable for most boll weevil overwintering habitats. As a result, ambient data often are used to estimate overwintering survival and emergence. In this study, relationship of ambient and overwintering habitat temperatures was determined for 6 habitats in the Rolling Plains of Texas. The amplitude of the daily temperature cycle in the leaf litter of each habitat was dampened compared with that recorded for ambient. Average minimum daily leaf litter temperature was 3.19"C higher in the shelterbelt habitat, followed by mesquite-grass pasture (3.54"C), tall shinnery motte (3.64"C), low shinnery brush (3.81°C), lovegrass (4.Ol0C), and pecan (6.01"C). Likewise, the average maximum daily leaf litter temperature was 3.77% lower in shelterbelt, followed by pecan (3.SSoC), lovegrass (3.87"C). mesquite-grass pasture (4.07"C), low shinnery brush (5.5loC), and tall shinnery motte (6.12"C). Stepwise multiple regression of hourly leaf litter temperatures explained 93% of the variability, with hourly ambient temperature and week of year being significant variables. Similarly, multiple regressions of daily leaf litter minimum temperatures and daily leaf litter maximum temperatures explained 96 and 90% of the variability, respectively, with ambient temperatures and week of year being significant variables for both regressions. The effect of temperature quality (ambient versus leaf litter) and sampling frequency (hourly versus daily) on positive (>6.1°C) and negative (<O.O"C) degree-days experienced by overwintering boll weevils was quantified for each of the 6 habitats for 4 yr of independent data, representing 2 mild and 2 severe winters. Degree-day calculations based on fitting minimum-maximum data to an asymmetrical double sine curve overestimated positive degree-day accumulation by 2.5%. Ambient temperature positive degree-days were similar to that for mesquite-grass pasture habitat, but the ambient temperatures overestimated positive degree-days experienced by overwintering weevils in the pecan by 6.5%. followed 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 ambient. Pecan leaf litter accumulated 99% fewer negative degree-days, followed by shelterbelt (95%), tall shinnery motte (88%), low shinnery brush (82%), lovegrass (71%), and mesquite-grass pasture (50%).

Effects of Planting Dates on Boll Weevils (Coleoptera: Curculionidae) and Cotton Fruit in the Subtropics

“…2003;andlate, 2 April 2002 and19 Mar. 2003. c of DD would require intimate knowledge of overwintering habitat and insulation, and ambient air temperatures overestimate positive DD by 6.5Ð15.7% (Parajulee et al 1997). Stone et al (1990) reported that, over a 7-yr study, the variation in emergence patterns can be Ͼ30 d. Although Parajulee et al (2001) developed a model for boll weevil survivorship on the Rolling Plains, overwintering habitats, food sources (Chandler and Wright 1991), the timing of weevil entry into overwintering habitat (Sterling 1971, Wade and, the date at which to begin calculating DD (Parajulee et al 1996), and the relative incidence of diapause, among other conceivable parameters, would differ in subtropical and tropical conditions where boll weevils are active and reproducing year-round (Guerra et al 1982).…”

Long-Term Seasonal Abundance Patterns of <I>Helicoverpa zea</I> and <I>Heliothis virescens</I> (Lepidoptera: Noctuidae) in the Texas High Plains

“…Positive degree-days (DD) (Ͼ0.0ЊC) were calculated using the daily minimum and maximum temperature method (Parajulee et al 1997). The threshold (0.0ЊC) for positive degree-days was estimated as the mean of the average daily minimum temperature between mid-February and early March, or just 2 wk immediately before the initiation of moth ßight to pheromone traps.…”

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

“…Among the years of study, 1980 was the coldest, with only 70 positive degree-days (DD) accumulated during the Þrst month of overwintering and 785 DD accumulated during the entire overwintering period of 185 d. In contrast, 336 and 1887 DD were accumulated during the Þrst month of overwintering and during the entire overwintering period of 188 d, respectively, in 1991. The total negative degree-days (NDD) also varied among years, ranging from 0 NDD in 1979, 1997, 1998, and 1999to 25 NDD in 1989. The amount of rainfall during each dig-up month ranged from 0 to 13 cm.…”

“…In the Texas Plains, boll weevils initiate diapause in early August (Sterling and Adkisson 1974), with spring/ summer emergence from overwintering habitats continuing to late July the following year Rummel 1985, Slosser andFuchs 1991). The proportion of diapausing weevils that successfully overwinter is dependent on boll weevil overwintering survival potential (Rummel et al 1999), timing of weevil entry into overwintering habitat (Sterling 1971, Wade and Rummel 1978, Rummel and Carroll 1983, Parajulee et al 1996, winter severity as reßected by low temperatures and rainfall (Pfrimmer and Merkl 1981, Price et al 1985, Stone et al 1990, and by the insulating capacity of the overwintering habitat (Slosser et al 1984, Slosser and Fuchs 1991, Carroll et al 1993, Parajulee et al 1997.…”