Magi Riba

Antifeedant activity of fruit and seed extracts ofMelia azedarach andazadirachta indica on larvae ofSesamia nonagrioides

Methanolic extracts of seeds and fruits of the chinaberry tree,Melia azedarach L. (Meliaceae), showed strong antifeedant activity against 2nd instar larvae ofSesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a very serious pest of maize(Zea mays L.) in Mediterranean countries. Extracts were applied in an artificial diet at concentrations of 1000 and 2000 ppm. The parameters used to evaluate the activity were larval growth rates; quantity of food ingested; phagodepression/phagostimulation index; quantity of frass produced; quantity of material ingested; duration of larval development; and cumulative mortality. Seed extract showed high bioactivity at both doses, while fruit extract proved to be less active, and only at the higher dose used (2000 ppm) did it display a slight antifeedant activity. The activity of theM. azedarach seed extract at the higher dose (2000 ppm) was comparable to that of pure azadirachtin applied at a dose of 1.25 ppm, or to ‘Mubel’, a commercial extract ofAzadirachta indica A. Juss. (Meliaceae), applied at a dose of 75 ppm.

Pheromone response inhibitors of the corn stalk borer Sesamia nonagrioides. Biological evaluation and toxicology.

The behavioral activity of some trifluoromethyl ketones (TFMKs) as inhibitors of the pheromone activity of the corn stalk borer Sesamia nonagrioides (Lef.) (Lepidoptera: Noctuidae) is reported. The most closely-related analogue to the pheromone tested, (Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:TFMK), elicited a significant decrease in the number of male catches in traps baited with mixtures with the pheromone in 1:1 and 10:1 ratios in comparison to the pheromone alone. The E isomer of the analogue as well as two highly hydrated ketones, 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) and 1,1-difluoropentadecyl trifluoromethyl ketone, were inactive. Conversely, the saturated TFMKs n-dodecyl trifluoromethyl ketone and, particularly, n-hexadecyl trifluoromethyl ketone induced a synergistic effect when mixed with the synthetic pheromone in 10:1 ratio. However, in a wind tunnel these chemicals did not elicit any differential effect on flying moths attracted to a source containing a 10:1 blend of the analogue and the pheromone. In a dual choice bioassay with two dispensers, containing the pheromone alone, and mixtures of Z11-16:TFMK and the pheromone and separated 5 cm apart, males showed no particular preference for either dispenser. The ketone mixture, however, induced moths to execute erratic flights with frequent crosswind counter-turns and intersections with plume boundaries. The total number of contacts with the source were reduced when a control dispenser was paired with a dispenser containing Z11-16:TFMK and pheromone. Z11-16:TFMK and OTFP showed little toxicity on mice with a LD50 of 1 g/kg after the 6th day of treatment. For comparitive purposes, the major component of the pheromone, Z11-16:Ac, displayed a LD50 of 5 g/kg 6 days after application. Our results provide additional information about the activity of the TFMKs, which might be useful for the utilization of these chemicals in future pest control studies.

Simple and stereoselective synthesis of sex pheromone of processionary mothThaumetopoea pityocampa (Denis and Schiff.)

A simple and stereoselective synthesis of (Z)-13-hexadecen-11-yn-1-yl acetate, the major component of the sex pheromone ofThaumetopoea pityocampa (Denis and Schiff.) is described. The procedure essentially involves formylation of a terminal acetylene to the corresponding aldehyde followed by a stereochemically controlled Wittig reaction, which has been studied under a variety of conditions.

Behavioural and electrophysiological responses of the European corn borer Ostrinia nubilalis to host-plant volatiles and related chemicals

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.

Initial field trials with the synthetic sex pheromone of the processionary mothThaumetopoea pityocampa (Denis and Schiff.)

Synthetic (Z)-13-hexadecen-11-ynyl acetate has been shown to be highly active in catchingThaumetopoea pityocampa (Denis and Schiff.) males in field trials carried out in different parts of Spain. A variety of formulations containing antioxidants or solid paraffin were tested. Formulations containing 3 and 10% ofE isomer showed a decrease of activity compared with those prepared with pureZ isomer. Dodecyl acetate, also found in the virgin female gland, did not show any synergistic effect when tested in a 9∶1 mixture with the synthetic pheromone. The product exhibited a remarkable persistence of activity under the field conditions even in the absence of stabilizer.

Development and biological activity of a new antagonist of the pheromone of the codling moth Cydia pomonella.

A new pheromone antagonist of the codling moth Cydia pomonella is reported. Presaturation of the antennae of the insects with vapors of the antagonist (E,E)-8,10-dodecadienyl trifluoromethyl ketone, analogue of the main component of the pheromone (codlemone), resulted in lower electrophysiological responses to the pheromone relative to untreated insects. In the wind tunnel, the compound elicited a remarkable disruptive effect on all types of behavior of males flying toward a source baited with a pheromone/antagonist blend in 1:1, 1:5, and 1:10 ratios. The insects displayed erratic flights in the presence of the antagonist, as shown by their flight parameters in comparison to insects attracted to the pheromone alone. In the field, traps baited with mixtures of 1:10 codlemone/antagonist attracted considerably lower numbers of males than the natural attractant. The antagonist, however, did not inhibit the pheromone-degrading enzymes present in male antennae, suggesting that trifluoromethyl ketones are not sufficiently electrophilic to produce a stable intermediate adduct with a cysteine residue of the enzyme, a mechanism previously proposed for oxidase inhibition in insects. Overall and taking into account our previous reports and, particularly, the reduction in damage induced in maize fields by a trifluoromethyl ketone analogue of the pheromone of Sesamia nonagrioides (Sole, J.; Sans, A.; Riba, M.; Rosa, E.; Bosch, M. P.; Barrot, M.; Palencia, J.; Castella, J.; Guerrero, A. Reduction of damage by the Mediterranean corn borer, Sesamia nonagrioides , and the European corn borer, Ostrinia nubilalis , in maize fields by a trifluoromethyl ketone pheromone analog . Entomol. Exp. Appl. 2008, 126, 28-39), the antagonist might be a new candidate to consider in future strategies to control the codling moth.

Identification of a minor component of the sex pheromone ofLeucoptera malifoliella (Lepidoptera, lyonetiidae)

A new minor component in the female volatile extract ofLeucoptera malifoliella (Costa) (Lepidoptera, Lyonetiidae) has been identified as 5,9-dimethyloctadecane (2). The amount detected of the minor compound2 ranged from 4 to 8% in comparison with the major component 5,9-dimethylheptadecane (1). Neither compound has been found in the male volatile extract. The identification has been based on its spectroscopic properties and Chromatographic behavior in comparison with an authentic synthetic sample. The synthesis has been carried out through a short route from 2,6-dimethylcyclohexanone (3). In field tests, compound2 appears to act as a Synergist of the major component1 when mixed with the latter in a 100∶0.1– 5 ratio.

Differential activity of non-fluorinated and fluorinated analogues of the European corn borer pheromone

Summary.The differing antagonist activity of (Z)-13-hexadecen-2-one (Z11 – 14 :MK, 1) and its 1,1,1-trifluoro derivative (Z11 –14 :TFMK, 2), two closely related analogues of the European corn borer pheromone Ostrinia nubilalis (Z strain), and their rationale is reported. Both chemicals exhibited some electrophysiological activity, and topical application of 10 pg of pheromone analogue on male antennae was sufficient to induce significantly lower depolarization responses to the pheromone versus untreated insects. In a wind tunnel, the number of European corn borer males attracted to sources containing mixtures of 1 + pheromone in ratios ≥ 1 :1 was significantly lower than the number attracted to a source containing pheromone alone. Source contact behaviour was dramatically impaired when the 1 + pheromone blend reached a ratio of 10 :1, in which only 2% of males displayed source contact in the presence of antagonist. When compound 1 was present at the source, males usually flew upwind with occasional downwind reversals; when compound 2 was present at the lure, males performed wider crosswind reversals, with little progress toward the source. In the field, traps baited with mixtures of both compounds with the pheromone in ratios of 5 :1 and 10 :1 elicited a significantly decreased number of male catches. In esterase inhibition assays, compound 2 was a potent inhibitor (IC50 = 70 nM), whereas the non-fluorinated compound 1 was not. The different activity of both compounds is presumed to be due to different mechanisms of action; considerations for using methyl ketone analogues as new behavioural antagonists of the pheromone are outlined.