Termination of Diapause in the Boll Weevil (Coleoptera: Curculionidae)

Dormancy of a specialist herbivore, Anthonomus rufipennis (Coleoptera: Curculionidae), in a dry tropical forest

The life history aspects of dormancy of the weevil Anthonomus rufipennis LeConte (Coleoptera: Curculionidae) were studied a 57-month period in a seasonally dry tropical forest of central Mexico. Weevil populations and their physiological status were monitored on both the reproductive host tree, Senna polyantha (Collad.) H.S: Irwin & Barneby (Fabales: Fabaceae) and the highly favored refuge host, Tillandsia recurvata L. (Poales: Bromeliaceae) or "ball moss." During the dry season, weevils were only found on the refuge host with a mean total density of 1.014 ± 2.532 individuals/ball moss (N = 1,681). Weevil densities on T. recurvata between early and late dry seasons were not significantly different, suggesting that dry season survival was relatively high. Weevils collected during these seasons revealed little reproductive development and relatively high-fat accumulation in both sexes. During 5 of 6 yr, densities of the weevils in T. recurvata dropped significantly during the early rainy seasons, when the reproductive host trees leafed out and began producing oviposition sites (flower buds). At this time, more males than females initially moved to vegetative trees and showed significant signs of reproductive development. Recolonization of ball moss by weevils began during the late rainy season when oviposition sites (flower buds) were still available. A proportion of the weevils remained on the reproductive host, suggesting that A. rufipennis is facultatively multivoltine. The methodologies and results of the study can serve as a model system for future studies of the dormancy of other insects in dry tropical forests and provide insight into the dormancy of other anthonomine weevils of economic importance.

Aseasonal, undirected migration in insects: 'Invisible' but common

Many insect pests are long-distance migrants, moving from lower latitudes where they overwinter to higher latitudes in spring to exploit superabundant, but seasonally ephemeral, host crops. These seasonal long-distance migration events are relatively easy to recognize, and justifiably garner much research attention. Evidence indicates several pest species that overwinter in diapause, and thus inhabit a year-round range, also engage in migratory flight, which is somewhat "invisible" because displacement is nondirectional and terminates among conspecifics. Support for aseasonal, undirected migration is related to recognizing true migratory flight behavior, which differs fundamentally from most other kinds of flight in that it is nonappetitive. Migrating adults are not searching for resources and migratory flight is not arrested by encounters with potential resources. The population-level consequence of aseasonal, undirected migration is spatial mixing of individuals within the larger metapopulation, which has important implications for population dynamics, gene flow, pest management, and insect resistance management.

Morphology and Morphometry of the Reproductive Tract of the Cotton Boll Weevil after Prolonged Feeding on Alternative Diets

Anthonomus grandis Boheman (Coleoptera: Curculionidae) survives on alternative diets; however, this induces reproductive diapause. The objective was to evaluate the morphology and morphometry of the reproductive tract of this weevil after feeding on alternative diets. The experimental design was completely randomized with 160 replications and treatments arranged in a factorial design 3 × 3, represented by A. grandis adults fed on 3 food types (fragments of banana (T1) or orange (T2) endocarp, or with cotton squares of cultivar BRS 286 (T3, control)) and three evaluation periods (30, 60, and 90 days) and after each of these periods they were fed with cotton squares for 10 days. The reproductive tract of 100% of A. grandis females fed banana endocarp, orange endocarp, and cotton squares for 30 and 60 days and then cotton squares were morphologically adequate for reproduction, and after 90 days, only 50% of those fed cotton squares were in this condition. The length of the ovarioles and the width of the mature oocyte were greater for A. grandis fed on cotton squares and smaller in those with banana and orange endocarps. Histological sections reveal that male testes even with strong degenerative signals are already producing spermatozoa. On the other hand, females displayed ovaries with nurse cells in the tropharium and some maturing oocytes in the vitellarium. The body length was longer and the testis area and diameter smaller in males fed on cotton squares than in those with banana and orange endocarp. Anthonomus grandis females fed for ≥90 days with alternative food sources do not recover the functionality of their reproductive tract, even after consuming, for 10 days, a diet that favors reproduction. On the other hand, the males remain with their reproductive organs functional with this condition.

Potential Distribution of Wild Host Plants of the Boll Weevil (Anthonomus grandis) in the United States and Mexico

The boll weevil (Anthonomus grandis Boheman) reproduces on a reported 13 species of wild host plants in North America, two in the United States and 12 in Mexico. The distributions of these plants are of economic importance to pest management and provide insight into the evolutionary history and origin of the BW. However, detailed information regarding the distributions of many of these species is lacking. In this article, we present distribution models for all of the reported significant BW host plants from Mexico and the United States using spatial distribution modelling software. Host plant distributions were divided into two groups: “eastern” and “western.” In Mexico, Hampea nutricia along the Gulf Coast was the most important of the eastern group, and the wild cottons, Gossypium aridum and Gossypium thurberi were most important in the western group. Other species of Hampea, Gossypium, and Cienfuegosia rosei have relatively restricted distributions and are of apparent minimal economic importance. Cienfuegosia drummondii is the only truly wild host in the southern United States, east of New Mexico. Factors determining potential distributions were variable and indicated that species were present in five vegetation types. Ecological and economic considerations of host plant distributions are discussed, as well as threats to host plant conservation.

Reproductive Dormancy in Overwintering Adult Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

Dormancy is important for overwintering insects to resist and adapt to adverse conditions. Dormancy generally contains quiescence and diapause. Eucryptorrhynchus brandti Harold (Coleoptera: Curculionidae), tree-of-heaven trunk weevil (TTW), is a destructive pest and highly host-specific to Ailanthus altissima in China. TTW has one generation per year and overwinters as both larvae and adults. In this study, to examined dormancy type of adults and find a method to store overwintering adults, we collected adults from 20 October 2018 to 13 March 2019. We studied the behavior and reproductive development of adults under field cold conditions for 0 and 10 d and laboratory warm conditions for 5 and 10 d. We recorded developing eggs in females, and the clarity of the testis edge, the yellow point in the testis lobe, the ratio of the inner content in the accessory gland, and the accessory gland color in males. Adults transferred from the field to the laboratory had resumed reproductive development directly. Results indicated that the dormancy type of TTW adults was quiescence. Adults stored in the field were still in a dormant state and the field-storage method was effective. Current study provided basic data for controlling overwintering TTW adults and solve the storage of insect sources during the winter.