No abstract

The mechanisms associated with resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), to organophosphate insecticides in pome fruit orchards have been shown to depend on the area. Our objectives were to evaluate the susceptibility of Spanish codling moth populations to chlorpyrifos-ethyl, azinphos-methyl, and phosalone, and the activity of three enzymatic systems reported to be involved in resistance. Eleven field populations and a susceptible strain used as a reference were tested using a bioassay consisting in the topical application of a diagnostic concentration on postdiapausing larvae. The enzymatic activity of mixed function oxidases (MFO), glutathione transferases (GST), and esterases (EST) was measured in postdiapausing larvae and adults. A significant decrease in the efficacy of the organophosphates was observed for all field populations, although the decrease was smaller in the case of chlorpyrifos-ethyl. No differences between sexes were detected. In postdiapausing larvae, the activity of the three enzymatic systems was higher in all the field populations than in the susceptible population. The possible implication of EST in codling moth insecticide resistance is reported for the first time in European field populations. In adults, only MFO and GST were implicated. Codling moth resistance to organophosphates in Spanish populations must be taken into account in the implementation of antiresistance strategies.

Insecticides are the dominant pest management method in fruit and vegetable crops worldwide owing to their quick effect, low cost, and relatively easy application, but they bear negative effects on human health and the environment. Insecticide mode of action (MoA), target species, and sex are variables that could affect insecticide-induced mortality. We recorded the mortality caused by three neurotoxic insecticides with different modes of action (chlorpyrifos [organophosphate, acetylcholinesterase inhibitor], λ-cyhalothrin [pyrethroid, sodium channel modulator], and thiacloprid [neonicotinoid, nicotinic acetylcholinesterase receptor agonist]) applied topically to adult males and females of three economically important tortricid species [Cydia pomonella (L.), Grapholita molesta (Busck), and Lobesia botrana (Denis & Schiffermüller)] that strongly depend on insecticide use for their control. Concentration and dose-mortality curves were recorded at 24 and 48 h postapplication. Large mortality differences between insecticides (maximum 7,800-fold for LD50) were followed by much lower, yet important, differences between species (maximum 115-fold), and sexes (maximum 41.5-fold). Significant interactions between the three factors indicate that they are not independent from each other. Interestingly, with the organophosphate chlorpyrifos, males of the three species were less susceptible than females, which was unexpected, as females are larger than males. Higher female sensitivity to organophosphates has been reported previously but only in G. molesta, not in other moth species. Our results highlight the importance of taking into account sex in dose-mortality studies with adult moths.

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.

Resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), to insecticides has become a major problem in many apple and pear production areas. Our aim was to determine the level of insecticide resistance in Spanish field populations. Seven field populations collected from apple, Malus domestica Borkhausen (Rosaceae), orchards, and three laboratory susceptible strains of codling moth were studied. Damage at harvest in all the conventional orchards from which codling moth populations were collected was higher than the economic threshold. The efficacy of eight insecticides, with five modes of action, was evaluated by topical application of the diagnostic concentrations on post‐diapausing larvae. The enzymatic activity of mixed‐function oxidases (MFOs), glutathione transferases (GSTs), and esterases (ESTs) was evaluated for each population. The susceptibility to insecticides and the biochemical activity of the three laboratory strains and one organic orchard population were not significantly different. Field populations were less susceptible to the tested insecticides than the susceptible strains, especially for azinphos‐methyl, diflubenzuron, fenoxycarb, and phosalone. The efficacy of all insecticides was significantly dependent on the activity of MFOs. Only the toxicity of the three insecticides most used in Spain when the populations were collected (azinphos‐methyl, fenoxycarb, and phosalone) was also dependent on the activity of ESTs and GSTs activity. We conclude that the control failures were because of the existence of populations resistant to the main insecticides used.

The response of Grapholita molesta (Busck) males to three-component sex pheromone blends containing a 100% ratio of the major sex pheromone component, (Z)-8-dodecenyl acetate and a 10% ratio of (Z)-8-dodecenol, but with varying ratios of (E)-8-dodecenyl acetate (0.4, 5.4, 10.4, 30.4, and 100.1% E-blends) was tested with populations in eight stone and pome fruit orchards in Europe, Asia, and North and South America. Traps baited with the 5.4% E-blend caught significantly more males than traps with any other blend with all populations. Significantly more males were caught in traps baited with the 10.4% E-blend than in traps with the remaining blends, except with the 0.4% E-blend in Turkey. Significant differences in male moth catches occurred between the other blends with the 0.4>30.4% E-blend, and the 30.4>100.1% E-blend. Male moth catches with the 100.1% E-blend only differed from the hexane control in Chile. No apparent differences were noted to these blends in populations collected from pome or stone fruits. Flight tunnel assays to synthetic blends with a subset of populations were similar to the field results, but the breadth of the most attractive E-blends was wider. Flight tunnel assays also demonstrated a high level of male-female cross-attraction among field-collected populations. Female gland extracts from field-collected populations did not show any significant variation in their three-component blends. The only exceptions in these assays were that long-term laboratory populations were less responsive and attractive, and produced different blend ratios of the two minor components than recently collected field populations.

Methyl isonicotinate is one of several patented 4-pyridyl carbonyl compounds being investigated for a variety of uses in thrips pest management. It is probably the most extensively studied thrips non-pheromone semiochemical, with field and glasshouse trapping experiments, and wind tunnel and Y-tube olfactometer studies in several countries demonstrating a behavioural response that results in increased trap capture of at least 12 thrips species, including the cosmopolitan virus vectors such as western flower thrips and onion thrips. Methyl isonicotinate has several of the characteristics that are required for an effective semiochemical tool and is being mainly used as a lure in combination with coloured sticky traps for enhanced monitoring of thrips in greenhouses. Research indicates that this non-pheromone semiochemical has the potential to be used for other thrips management strategies such as mass trapping, lure and kill, lure and infect, and as a behavioural synergist in conjunction with insecticides, in a range of indoor and outdoor crops.

Several sympatric lepidopteran species feed on maize plants, and the different components of their species-specific female sex pheromones may play a role in attracting conspecifics and/or deter heterospecific males. In this study, we analyzed the content of Mythimna unipuncta pheromone glands and tested the response of males to components of their own pheromone blend and that of Sesamia nonagrioides in the wind tunnel. Whole pheromone glands, and lures where (Z)-9-hexadecenyl acetate, Z)-11-hexadecen-1-ol or (Z)-9-hexadecenyl acetate + (Z)-11-hexadecen-1-ol were added to the major component, (Z)-11-hexadecenyl acetate, elicited significantly higher responses by M. unipuncta males than lures with main component alone, although the levels varied with concentration. In the field a rather different outcome was observed, as the addition of other compounds found in the female pheromone gland did not improve trap catch over lures with only (Z)-11-hexadecenyl acetate. The addition of (Z)-11-hexadecenal, a compound of the S. nonagrioides pheromone, to (Z)-11-hexadecenyl acetate significantly reduced attraction of M. unipuncta males both in the wind tunnel and in the field, as well as the number of sympatric clover cutworm, Discestra trifolii, under field conditions. The addition of (Z)-9-hexadecenyl acetate, a minor component of the M. unipuncta pheromone blend, reduced the number of S. nonagrioides captured in field traps that were baited with the S. nonagrioides lure. The significance of such inhibition in the reproductive isolation of sympatric species that attack maize is discussed.