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

Abstract

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is an important pest of cotton (Gossypium spp. (Malvales: Malvaceae)) in South America, Mexico, and southernmost Texas in the United States. A key factor in the persistence of the boll weevil is its ability to survive the noncotton season. Mechanisms facilitating this survival in subtropical and tropical areas are incompletely known, and our understanding has been further complicated by recent reports of overwintering on noncotton hosts. In addition, the nature and even existence of the adult dormancy, and validity of the criteria used to distinguish it, have been questioned. We manipulated the boll weevil diet to produce a range of diapause responses and observed the corresponding host-free survival patterns. The estimated proportion of diapause was associated with subsequent survival. In addition, different diets producing similar incidences of diapause resulted in substantially different host-free longevity, and the longest survival was observed for weevils fed bolls as adults. Survival patterns exhibited a negative temperature dependence except for the lowest observed temperature (12.8°C), where survival was reduced compared with that at 18.3°C. This suggests chronic chilling injury in response to extended exposure to low, above freezing temperatures. All but the highest temperature (29.4°C) facilitated survival >6 mo, and survival of >1 yr was observed at 18.3°C. The temperatures permitting the greatest survival are typical for many subtropical and tropical regions during the noncotton season, indicating that diapausing boll weevils are capable of surviving the noncotton season in these regions without the benefit of presumptive noncotton hosts.

Diapause Response of the Boll Weevil (Coleoptera: Curculionidae) to Feeding Period Duration and Cotton Square Size

“…The induction of diapause observed in this study in response to manipulations of diet under a photophase considered to suppress diapause was consistent with reports by Spurgeon and Raulston (2006) and Spurgeon and Suh (2017 , 2018 ). The apparent dependency of diapause incidence on age at assessment for male boll weevils was also consistent with temporal patterns reported for ranges of ages ( Spurgeon and Raulston 2006 ) or feeding period temperatures ( Spurgeon and Suh 2017 ) different from those used in this study.…”

“…4 ) and subsequent survival ( Fig. 6a ) for weevils fed large squares compared with those fed small squares were similar to the patterns reported by Spurgeon and Suh (2018) .…”

“…The present experiments incorporated a longer feeding period (21 d) than was used by Spurgeon and Raulston (2006) or Spurgeon and Suh (2017 , 2018 ). Reduced incidence of diapause after a 21-d feeding period, compared with a 14-d period, was demonstrated after adjustment for multiplicity only for males in the second study ( Fig.…”

“…Infested squares were held within environmental chambers at 29.4 ± 2°C with a 13:11 (L:D) h photoperiod until periodic examinations indicated the presence of pupae. These rearing conditions were selected for consistency with earlier reports ( Spurgeon and Raulston 2006 ; Spurgeon and Suh 2017 , 2018 ). In addition, day length during crop maturation and harvest, when diapause would be induced, is longer than 12 h in the southern portions of the boll weevil range in Texas.…”

“…Both of these effects (feeding duration, square size) were combined with temperature (12.8, 18.3, 23.9, or 29.4°, ±1°C) in the subsequent examination of host-free survival. These temperatures were selected for consistency with those used by Spurgeon and Suh (2018) . Each combination of square size and feeding duration was represented by four cartons (replications) of weevils of each sex (a total of 48 cartons of 40 weevils each).…”