The antagonistic effect on the pheromone response and catabolism of male European corn borers, Ostrinia nubilalis, by several trifluoromethyl ketones is reported. (Z)-11-Tetradecenyl trifluoromethyl ketone (Z11-14:TFMK), the most closely related analogue of the main component of the pheromone, elicits a remarkable disruptive effect on close approach and source contact of males flying to a source baited with mixtures of the pheromone and the antagonist in 5:1 and 10:1 ratios. In this experiment, the male displayed an erratic flight track with frequent counter turns and intersections with the plume. In the field, the TFMK significantly lowered the number of males caught when mixed with the pheromone in a 10:1 ratio in comparison with the natural attractant. The compound was also a good inhibitor of the antennal esterase of the insect with a IC(50) value of 0.28 muM. The homologous (Z)-10-tridecenyl trifluoromethyl ketone, with one carbon less in the chain, also elicited an antagonistic effect in the wind tunnel, but in the field, the results were not conclusive. The effect induced was lower than the one displayed by Z11-14:TFMK including the activity as the esterase inhibitor (IC(50) value of 7.55 muM). The saturated tetradecyl trifluoromethyl ketone, tetradecyltrifluoropyruvamide, and (Z)-11-2-thiatetradecenyl trifluoromethyl ketone resulted completely inactive. The results obtained in conjunction to the previously shown low toxicity to mice by related trifluoromethyl ketones provide new important data for the putative utilization of these chemicals as new pest control agents.

No abstract

Large-scale field experiments on the Mediterranean corn borer, Sesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), were carried out in 2004 -2006 on maize [ Zea mays L. (Poaceae)] fields using ( Z )-11-hexadecenyl trifluoromethyl ketone, an antagonist analog of the pheromone of this species, to evaluate a possible reduction of damage caused by this pest. The effect of the treatments on the European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), a sympatric species, was also determined. Evaluation of the success of the experiments was assessed by counting (i) the number of males caught by pheromone traps in treated and untreated fields, (ii) the number of plants attacked by both insects in both plots, and (iii) the number of larvae present in infested plants in both fields. Effectiveness of the treatment was high for the second generation of the Mediterranean corn borer, the most harmful to the crop (86 -90% reduction in the number of plants attacked and 67 -98% reduction in the number of larvae per plant in treated fields in comparison to untreated fields), and moderate for the third generation (reduction of 41-71% and 33 -77%, respectively). Treatments were also effective for the second generation of the European corn borer (61 -75% reduction in the number of plants attacked, 58 -78% reduction in the number of larvae found per plant) as well as for the third generation (69 -97% and 70 -98% reduction, respectively). By plotting the amount of the antagonist remaining on the dispensers after 40 -45 days of exposure with time, the mean release rate of the compound was calculated to be 2.2%/day in 2004, 1.95%/day in 2005, and 2.1%/day in 2006, with 26% of the initial compound remaining after 20 days of experimentation. The emission rate appears to cover the flight of the most damaging second generation of both insects. Prospects of using trifluoromethyl ketones as new potential agents for pest control are also outlined.

The European corn borer Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) is a worldwide pest of maize (Zea mays L.) and other crops. The semiochemicals released by maize plants and structurally-related compounds can be used by adult female O. nubilalis for host-plant location and oviposition. Headspace volatile compounds emitted by watered and water-deprived maize plants are collected and identified by their retention indices and mass spectra. The most abundant compounds from watered plants are limonene, linalool, benzoic acid, indole, β-caryophyllene and acetophenone, whereas, in water-deprived plants, limonene, acetophenone, hexanoic acid, benzoic acid and indole are dominant. In addition, (E )-4,8-dimethyl-1,3,7-nonatriene, 6-methyl-5-hepten-2-one, anisole and 1-carvone are undetected in the water-deprived plants. Some of the identified compounds show electrophysiological activity (electroantennogram) in the antennae of both sexes, with the responses elicited by tridecane, tetradecane, dodecane, nonanal, decanal and 2-ethylhexanol on males being particularly noteworthy. In a dual-choice olfactometer, adult females show a preference for 2-hexanol, heptanal, methyl salicylate, hexyl acetate, nonanal, methyl dodecanoate, β-pinene and (E )-2-hexenyl acetate over hexane controls. Tetradecane, linalool, methyl hexanoate, methyl nonanoate, (Z )-3-hexenyl benzoate, tridecane, 2-cyclopentylcyclopentanone, 3-methylbutyl acetate, β-myrcene and (Z )-3-hexenyl butanoate result in fewer females in the test arm compared with the control arm. No single compound displays an activity similar to watered maize plants, supporting the hypothesis that blends of volatiles in specific ratios are more effective than single volatile chemicals. The results of the present study suggest that methyl salicylate, which elicits also one of the highest electrophysiological responses in female antennae, plays a role in host preference by O. nubilalis females.