Diapause in the Boll Weevil (Coleoptera: Curculionidae): Seasonal Occurrence in Mississippi Populations

Abstract

This study examines the diapause response among boll weevils collected as immatures in squares at different times of the summer and held under simulated field photoperiods and temperatures of northern Mississippi. The percentage of adults exhibiting prediapause increased seasonally, starting with the 1st generation in July and achieving a maximal rate of 96.7% late in the year. A greater proportion of males achieved diapause than females at any given time, except late in the season when convergence in the diapause response of both sexes occurred. These results suggest that individuals in a population have different thresholds of sensitivity to the environmental cues regulating the onset of diapause. Models described the percentage of males and females in prediapause as a function of Julian date of emergence and daylength on the day of emergence. The latter models have potential application over a wide region of the Cotton Belt. Information from this study was used to suggest August starting dates for diapause control applications in the mid-Southrecommendations that subsequently were implemented in eradication programs in Alabama and Mississippi.

Diapause in the Boll Weevil (Coleoptera: Curculionidae): Life-Stage Sensitivity to Environmental Cues

“…Rearing containers were placed in environmental cabinets within which the temperature and lights were computer controlled using instructions described by Wagner and Villavaso (1999). Immature and adult boll weevils were held under simulated field temperatures and photoperiods of north Mississippi.…”

“…The proportions of reproductive and prediapausing adults were calculated after excluding indeterminate weevils. Percentages of prediapausing males and females in each treatment group were plotted (dependent variable) at their respective mean emergence dates (independent variable) and compared with control data found in Wagner and Villavaso (1999). Treatment effects were also compared with the expected seasonal trends of diapause among males and females described by the logistic equations from Wagner and Villavaso (…”

“…Weather in the mid-South is variable, and patterns of above and below normal temperatures are common throughout the year. If temperature influences diapause, especially during the adult stage as suggested by Earle and Newsom (1964), Lloyd et al (1967)) and Cobb and Bass ( 1968)) then seasonal patterns may account for some of the variability observed in the process (see Wagner and Villavaso 1999). To examine the effects of above-normal temperatures on diapause, a portion of adults emerging from a late-season environment were transferred to a cabinet simulating temperatures 60 d earlier and much warmer than the controls (see Fig.…”

“…Past research on boll weevil diapause sought to identify the primary token stimuli responsible for its initiation, and although this research generally identifies photoperiod, temperature, and host/diet as influencing factors, the exact influence of these variables on individual weevil life stages is poorly understood (see Wagner and Villavaso 1999). One reason for this situation is the lack of consistent and rigorous experimental design.…”

“…The effectiveness of the stimuli and the sensitivity of the stage(s) perceiving the stimuli may influence the depth and, thus, the duration of diapause. If the boll weevil responds to multiple environmental cues over its life cycle, as suggested by the literature (Wagner and Villavaso 1999)) then the application of artificial (unnatural) procedures to study diapause would contribute to (help explain) the variable responses observed within and among studies.…”