Emergence of Overwintered Boll Weevils (Coleoptera: Curculionidae) in Relation to Microclimatic Factors

Abstract

The boll weevil, Anthonomus grandis Boheman, enters a diapause state to survive winters in temperate regions and subsequently emerges from overwintering habitats to infest squaring cotton in the spring. Previous research has found that boll weevil overwintering emergence is closely associated with climatic patterns of temperature and precipitation. The objectives of this study were to determine the effects of temperature, humidity, and other meteorological factors on the temporal pattern of boll weevil emergence, and to compare the physiological and morphological conditions of emerged and trapped weevils. Emergence cages were infested with diapausing weevils in the fall. Daily emergence and microclimatic conditions of the leaf litter and air were monitored until the subsequent summer. Air temperature and relative humidity, incident solar radiation, and precipitation were signiÞcantly greater on emergence dates than on dates with no emergence. Emerged and trapped weevils were dissected to assess their morphology. Emerged weevils tended to exhibit greater fat body development, a higher frequency of testicular atrophy, and less ovary development than trapped weevils. None of the emerged weevils were rated extra lean and no trapped weevils were rated fat. These results are consistent with previously-reported effects of climatic factors on weevil emergence in other areas of the Cotton Belt, and add new information about the physiological and morphological characteristics of emerged weevils. This information on the dynamics and mechanisms of overwintering provides insight that should be helpful in formulating improved predictive models, risk assessments, and management strategies for the boll weevil.

Temperature Influences on Diapause Induction and Survival in the Boll Weevil (Coleoptera: Curculionidae)

“…The higher host-free survival rates of males compared with females are difficult to interpret unambiguously, especially considering that several previous studies using either vegetative stage cotton as food ( Esquivel et al 2004 , Suh and Spurgeon 2006 ) or observations of survival under ambient conditions ( Westbrook et al 2003 , Spurgeon 2008 ) did not report similar differences. Regardless, differences observed in this study occurred early in the host-free survival period.…”

Morphology, Diet, and Temperature-Dependent Host-Free Survival of the Boll Weevil, Anthonomus grandis (Coleoptera: Curculionidae)

“…However, their feeding period duration was too long (48 d) to produce a good estimate of potential host-free longevity because many of the weevils that did not enter diapause would have died before the end of the feeding period. Most other studies of overwintering survival have been conducted under uncontrolled field conditions or used a mixture of food types ( Fenton and Dunnam 1927 ; Gaines 1959 ; Rummel and Carroll 1983 ; Carroll et al 1993 ; Parajulee et al 1996 , 1997 ; Westbrook et al 2003 ; Spurgeon 2008 ), so comparisons with our results are not possible. In contrast, Spurgeon and Suh (2017) fed a cotton boll diet similar to the diet we used, and observed host-free survival at 23.9°C that was very similar to the survival we observed in this study.…”

Host-Free Survival of Boll Weevils (Coleoptera: Curculionidae) Previously Fed Vegetative-Stage Regrowth Cotton

“…Taub-Montemayor et al (1997) produced putative diapausing weevils by exposing unfed newly-emerged weevils to a photoperiod of 12:12 h and a thermoperiod of 26:21°C [L:D], but none of the weevils survived beyond 10 d. Finally. Spurgeon and Raulston (1998a) and Spurgeon and Esquivel (2000) found that feeding regimen could be manipulated to control the diapause response, and their techniques were used to produce high levels of overwintering survival (45-73%) in field studies (Westbrook et al 2003), and to identify and characterize a storage protein diagnostic of diapause in boll weevils (Lewis et al 2002). Spurgeon et al (2003) suggested that failure to recognize the respective fat body types characteristic of newly eclosed, reproductive, and diapausing weevils has likely contributed to confusion in the literature.…”