Structural Insights into the Ligand-Binding and -Releasing Mechanism of Helicoverpa armigera Pheromone-Binding Protein PBP1

Cotton bollworm (Helicoverpa armigera) is a worldwide agricultural pest in which the transport of pheromones is indispensable and perceived by pheromone-binding proteins (PBPs). However, three-dimensional structure, pheromone binding, and releasing mechanisms of PBPs are not completely illustrated. Here, we solved three structures of the cotton bollworm HarmPBP1 at different pH values and its complex with ligand, Z-9-hexadecenal. Although apo-HarmPBP1 adopts a common PBP scaffold of six α-helices surrounding a predominantly hydrophobic central pocket, the conformation is greatly distinct from other apo-PBPs. The Z-9-hexadecenal is bound mainly by hydrophobic interaction. The pheromone can enter this cavity through an opening between the helices α5 and α6, as well as the loop between α3 and α4. Structural analysis suggests that ligand entry into the pocket is followed by a shift of Lys94 and Lys138, which may act as a lid at the opening of the pocket. Acidic pH will cause a subtle structural change of the lid, which in turn affects its ligand-binding ability, differently from other family proteins. Taken together, this study provides structural bases for the interactions between pheromones and PBPs, the pH-induced conformational switch, and the design of small inhibitors to control cotton bollworms by disrupting male–female chemosensory communication.

Alternative Methods of Ant (Hymenoptera: Formicidae) Control with Emphasis on the Argentine Ant, Linepithema humile

Simple Summary

Ants can be major pests to homeowners and other property owners. In the U.S., ants often rank as one of the most common and difficult-to-control pests around and in homes, businesses, and other facilities. Typically, ant control practices are conducted by licensed pest management professionals with sprays, baits, and granular products, containing various types of insecticides, applied to the outside perimeter of infested structures. Many of the insecticides used to control pest ants are harmful to non-target organisms, especially those in aquatic environments. To address these negative environmental impacts, research on alternative, generally low-impact and least toxic, ant control strategies has received a fair amount of attention. The underlying goal of this research is a reduction in human exposure to traditional insecticides. Examples of alternative approaches included in this review article include the use of essential oils and other chemicals as deterrents to ant nesting and foraging; ant trail pheromones as disruptants to foraging; mass trapping of ants; new gel baits containing extremely low concentrations of insecticide; and altering the behavior and distribution of ants by altering their access to food.

Abstract

Ants (Hymenoptera: Formicidae), especially the Argentine ant, Linepithema humile (Mayr), can be significant nuisance pests in urban and suburban environments. Conventional interventions have primarily relied on the use of chemical insecticides, namely fipronil and bifenthrin, applied as residual, contact treatments around the outside perimeter of infested structures. Despite tightening regulation limiting the scope of insecticide applications in urban settings, dependence on these products to manage ants continues, resulting in significant water contamination. The U.S. EPA, in response, has further restricted the use patterns of many insecticides used for ant control in professional and over-the-counter markets. The purpose of this review is to summarize the relevant literature associated with controlling nuisance pest ants, with emphasis on L. humile, without the use of liquid broadcast applications of EPA-registered insecticides while focusing on low-impact, alternative (to broadcast applications) pest control methods. Specific subsections include Trail Pheromone; Use of Behavior-Modifying Chemicals; Mass Trapping; Hydrogels, “Virtual” Baiting, and Exceedingly-Low Bait Concentrations; Food Source Reduction; Deterrents; and RNA Interference (RNAi).

Development of a Pheromone-Assisted Baiting Technique for Argentine Ants (Hymenoptera: Formicidae)

Current control measures for Argentine ants, Linepithema humile (Mayr), in urban settings typically include perimeter applications of insecticides around structures, resulting in potential problems with insecticide runoff and environmental contamination. Insecticidal baits can be an effective alternative to perimeter spray applications and are largely considered target-specific with minimal nontarget impact and environmental contamination. We report a "pheromone-assisted baiting technique" as an economically viable approach to maximize the efficacy of conventional baits targeting Argentine ants. Laboratory experiments with a commercially available gel bait indicated that foraging activity and final mortality of Argentine ants were significantly improved by incorporating (Z)-9-hexadecenal in the bait. The field study demonstrated that the pheromone-treated gel bait achieved a 74% reduction in Argentine ant activity by the end of 4 wk when it was compared with its own pretreatment value. This was a significant improvement over the untreated gel bait that provided a 42% reduction over the same period of time. The pheromone-assisted baiting technique has the potential in providing effective ant control with reduced amount of insecticides applied in the environment.