Activity of octylthiotrifluoropropan-2-one, a potent esterase inhibitor, on growth, development, and intraspecific communication in Spodoptera littoralis and Sesamia nonagrioides

Effect of Treatment With 3-Octylthio-1,1,1-Trifluoropropan-2-One in the Diamondback Moth (Lepidoptera: Plutellidae) to the Toxicity of Diafenthiuron, Indoxacarb, and Bacillus thuringiensis

The diamondback moth, Plutella xylostella (L.), is a worldwide insect pest of cruciferous crops. Although insecticides have long been used for its control, diamondback moth rapidly evolves resistance to almost any insecticide. In insects, juvenile hormone (JH) is critically involved in almost all biological processes. The correct activity of JH depends on the precise regulation of its titer, and juvenile hormone esterase (JHE) is the key regulator. Thus, JH and JHE have become important targets for new insecticide development. Trifluoromethyl ketones are specific JHE inhibitors, among which 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) has the highest activity. The interaction effects between pretreatment with or combination of OTFP and the insecticides diafenthiuron, indoxacarb, and Bacillus thuringiensis (Bt) were investigated in diamondback moth larvae to determine OTFP's potential as an insecticide synergist. In third-instar larvae, both pretreatment and combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron, indoxacarb, and Bt at all set concentrations. In fourth-instar larvae, combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron and indoxacarb at all set concentrations. However, it increased or synergized the toxicity of Bt at lower concentrations despite the limited effect at higher concentrations. Our results indicated that the effect of OTFP on the toxicities of insecticides varied with the type and concentration, larval stage, and treatment method. These findings contribute to the better use of OTFP in diamondback moth control.

Synthesis, Functional Assays, Electrophysiological Activity, and Field Tests of Pheromone Antagonists of the Tomato Leafminer, Tuta absoluta

The tomato leafminer, Tuta absoluta, is one of the major pests of tomato and other Solanaceae in many regions worldwide. In the search for new strategies to control this pest, we present herewith the stereoselective synthesis, electrophysiological activity, functional analysis, and field tests of new chemicals as possible antagonists of the sex pheromone of the leafminer. The chemicals are methyl ketone (MK) and trifluoromethyl ketone (TFMK) structural analogues of both components of the pheromone. Most of the chemicals exerted per se some electrophysiological activity and inhibited the electroantennographic response to the pheromone when vapors of the inhibitor were passed over the antennae. Except TFMK 3, which elicited a modest effect, the compounds did not exhibit antiesterase activity on the pheromone-degrading enzymes of the antennae, but in the field the chemicals, particularly MK 5, notably decreased the number of catches when mixed with the pheromone in 1:1 and 10:1 ratios, regardless the infestation level of the plot. These results suggest that MK 5 is a good behavioral antagonist of the pheromone to be considered as a putative agent to control the pest in new future integrated pest management (IPM) strategies.

New pheromones and insect control strategies

A survey of the new environmentally safe strategies used for insect control is presented. The survey includes mating disruption, pheromone antagonists as chemical communication inhibitors, pheromones and plant-based volatiles, attractant-and-kill, and push-pull strategies. Important successes have been obtained, particularly in mating disruption with significant reduction in pesticide use in low to moderate pest infestations. One important factor of concern is the high cost of semiochemicals and formulations containing them in comparison to the conventional insecticide treatments, and a combined effort by scientists, producers, and farmers should be made to reduce the cost of application of these semiochemicals.