Starvation-induced morphological responses of the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae)

Authors: Spurgeon, Dale; Suh, Charles

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2017
Publication Date: 1/31/2018
Citation: Spurgeon, D.W., Suh, C.P. 2018. Starvation-induced morphological responses of the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae). Journal of Cotton Science. 21:275-283.

Interpretive Summary: Status of the boll weevil as a pest of cotton in the United States has diminished because of progress by eradication programs. However, this pest remains of critical importance in South America, and intractable populations in extreme South Texas and northern Mexico persistently threaten reinfestation of adjoining eradicated regions. The pheromone trap is an essential tool for detecting boll weevil infestations in eradication and management programs, and captures by the traps are also used to infer aspects of weevil ecology. However, interpretation of trap captures requires assumptions regarding how well captured weevils represent the larger population in the area. ARS scientists at Maricopa, AZ and College Station, TX identified key internal physical characteristics of boll weevils that provide information regarding the likely origin of captured weevils. Glands in the males that are associated with pheromone production, presence of eggs in females, and evidence of the reabsorption of yolk in developing eggs were particularly informative provided the interval between checking the traps is not more than two days. When the trap-checking interval is appropriately short, these characters offer the potential to distinguish weevils originating locally from those migrating from other areas. Utilization of these findings could improve the quality of ecological information obtained from captured weevils, and the effectiveness and cost-efficiency of actions by eradication programs to remediate reinfestations in eradicated regions.

Technical Abstract: Status of the boll weevil, Anthonomus grandis grandis Boheman, as a pest of cotton (Gossypium spp.) in the United States has diminished because of progress by eradication programs. However, this pest remains of critical importance in South America, and intractable populations in extreme South Texas and northern Mexico persistently threaten reinfestation of adjoining eradicated regions. The pheromone trap is an essential tool for detecting boll weevil infestations in eradication and management programs, and captures by the traps are also used to infer aspects of weevil ecology. Information provided by traps might be more interpretable if reliable morphological indicators can be identified from captured weevils, and less ambiguous if appropriate trapping intervals were identified to maximize the usefulness of those characters. Because captured boll weevils are isolated from food, key aspects of internal morphology were observed for informational potential based on their sensitivity to change in response to starvation. Condition of the midgut, presence of well-developed accessory glands in males, and presence of eggs as well as oosorption of vitellogenic oocytes in females, were particularly responsive to starvation. However, utility of these characters in interpretation of trap captures will require assessment of weevils that have been in the traps for no more than 1–2 d. Provided recently captured weevils are assessed, the characters we identify as indicative of a local source of weevils could improve the ecological information inferred from trap captures, and improve the effectiveness and cost-efficiency of remedial actions in eradication programs.