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

Abstract

Distribution of the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), in the United States has been greatly reduced by eradication efforts. Still, it remains a key pest of cotton (Gossypium spp., [Malvales: Malvaceae]) in the New World, and has proven difficult to eliminate from Mexico and from southern Texas. In those regions, improved knowledge of boll weevil overwintering ecology may benefit efforts by eradication and management programs. Adult diapause in the boll weevil is well documented, but influences of the feeding period duration between adult eclosion and assessment of diapause remain unstudied. We examined diapause incidence and associated survival for weevils fed for 7, 14, or 21 d after adult eclosion. Diapause incidence of females was less influenced by feeding duration compared with males. For males, highest diapause incidence occurred after 14 d of feeding compared with 7 or 21 d. Host-free survival tended to be higher after 14 d of feeding compared with 7 or 21 d, although many weevils were long-lived (≥80 d) after each feeding period duration. Males exhibited higher survival compared with females, and survival was higher for weevils fed large flower buds (squares) compared with smaller squares. Survival was most influenced by temperature; longevity increased with decreasing temperature except at the lowest temperature (12.8°C). These results suggest an optimal feeding period for induction of diapause and maximized host-free longevity. These findings may permit improved timing of late-season insecticide treatments aimed at reducing overwintering populations, and thereby improve effectiveness of eradication and management programs.

Differences in the Development of Internal Reproductive Organs, Feeding Amount and Nutrient Storage between Pre-Diapause and Pre-Reproductive Harmonia axyridis Adults

“…Sufficient nutrient storage before diapause is not only essential for diapause initiation and maintenance, but also for post-diapause fitness [24,28,37]. For example, sufficient food is necessary for both the boll weevil Anthonomus grandis grandis and two-spotted spider mite Tetranychus urticae Koch to enter diapause [38,39]. Bark beetles Ips typographus, with less nutrient reserves, have higher mortality and lower post-diapause fitness [40].…”

Fungal seed treatments of cotton affect boll weevil development

“…The field-collected squares, bolls, and emerging insects were held in cages in a controlled environment room (29 °C, 60% relative humidity, and 13 h light:11 h dark photoperiod) inside a quarantine facility located at the Texas A&M AgriLife Research and Extension Center in Weslaco, TX. 32,33 Pupae were collected daily from infested squares and bolls. Five pupae were placed in 10-cm Petri dishes containing a thin layer of moistened vermiculite.…”

“…Dishes were checked twice a day for newly eclosed adults, which were sexed using the tergal-notch method. [33][34][35] Females were marked on the left elytron using a nontoxic finetip white paint pen (Speedball Painters, Hunt Manufacturing, Statesville, NC, USA) to distinguish adults after mating. 33 Sexed adults were transferred to cages with around 40 weevils of the same cohort containing a water-soaked cotton wick and were provided with clean, 5-9 mm diameter bracteole-free squares at a rate of 1 square/5 weevils.…”

“…Fresh squares were provided daily. 33,36,37 Immediately prior to use in experiments, groups of 20 mixed-sex weevils (sex ratio 1:1) were randomly selected from cages and transferred into separate 15-cm Petri dishes with a meshed lid. 38 Adults were allowed to mate for 48 h to maximize the possibility of fertilization.…”

“…Infested squares and bolls from each cage for greenhouse assays were held separately in 50-mL cups with a moistened filter paper to minimize the desiccation of reproductive structures, which would interfere with immature development. 32 The reproductive structures were checked for newly emerged pupa, which were collected and placed in Petri dishes with a layer of moistened vermiculite, 33 and the developmental time (days) to adult and from oviposition to pupa was recorded. Newly-eclosed adults (<24 h old) were separated by sex using the tergal-notch method, 33,35 weighed, and the length between the head and abdomen was measured.…”