Only a few of the registered insecticides against Cydia pomonella L. are still effective in areas where insecticide resistance has emerged in this pest. Resistance mechanisms are multiple, and their lone or cumulative effects in a single population are not completely understood. A detailed estimation of resistance spectrum is still required to define the suitable insecticides to use against a given population. The efficacy of ten insecticides was therefore investigated together with the resistance mechanisms expressed in four laboratory strains and 47 field populations of C. pomonella from five countries. Bioassays were performed using topical applications of diagnostic concentrations on diapausing larvae, and resistance mechanisms were analysed on adults emerging from control insects. All populations exhibited a reduced susceptibility to at least one insecticide when compared with the susceptible laboratory strain. Cross-resistances were observed between azinphos-methyl or phosalone and more recent compounds such as spinosad and thiacloprid. Resistances to azinphos-methyl, diflubenzuron, spinosad, tebufenozide and thiacloprid were significantly correlated with mixed-function oxidase activity, while increased glutathione-S-transferase and reduced non-specific esterase activities were correlated with resistance to azinphos-methyl and emamectin, respectively. Conversely, resistances to azinphos-methyl, tebufenozide and thiacloprid were negatively correlated with increased esterase activity. None of the observed mechanisms explained the loss of susceptibility of populations to chlorpyrifos-ethyl, and no significant correlation was detected between resistance to deltamethrin and the presence of the kdr mutation. The suitability of such non-target instars to monitor insecticide resistance in field populations is discussed.

The attract and kill technique has been formulated in a product under the trade name 'Sirene CM '. It consists of a viscous paste containing 0.16% codlemone to attract the male moths and 6.0% permethrin to kill them. The formulation is applied by hand twice per season using a specially developed system which can be calibrated for application of the paste to the host plant in small droplets of either 100 µl or 50 µl. Between 1995 and 1997, 15 trials on control of the codling moth were conducted in isolated orchards in the Lake Geneva region. In each plot, depending on tree size, two applications varying between 52 and 537 g ha −1 of Sirene CM were made. In 14 trials, the larval attack of the codling moth on fruit was below the economic threshold of 1% and the hibernating population stayed at a low level. One single plot (0.4 ha) had to be treated with a curative spray in 1995, because the initial population was much too high. According to the reductions in trap catch and of mating frequency measured by tethered codling moth females, efficiency of the attract and kill droplets lasted 5-7 weeks, after which it decreased slowly.

Four populations of codling moth Cydia pomonella L. were collected as overwintering larvae from apple orchards with different pesticide pressure (S. Michele, Roncafort, Revo`and Vervo`) in the Trento province (northern Italy). Mortality rate caused by a predetermined discriminating concentration of tebufenozide topically applied on overwintering larvae was evaluated. Neonate F1 progeny of the same populations were assayed for susceptibility to tebufenozide by feeding them on thinning apples treated with an appropriate discriminating dose of the insecticide. The activities of the main enzyme systems involved in the detoxification of insecticides were also evaluated in each population and related to their susceptibility to tebufenozide. The topical test detected a significant loss in susceptibility to tebufenozide in two populations, S. Michele and Roncafort, while all the overwintering larvae collected in the orchards of Revo`and Vervo`died when treated topically with the discriminating concentration. The apple-dipping test performed on the neonate larvae showed a highly significant reduction in the susceptibility of the two populations of S. Michele and Roncafort. A less significant reduction in mortality rate was found in the Revo`population; however, no statistical difference was found between the Vervo`population and the susceptible reference. None of the four field populations significantly differed from the susceptible strain for Glutathione-S-transferase and esterase activity. A significantly higher frequency of individuals of the S. Michele and Roncafort populations exhibited a higher mixed function oxidase activity than the susceptible strain. The small resistance ratio values found for the two populations together with the low frequency of individuals exibiting enhanced enzymatic activity, reveals that the selection process was still at the early stage. Because of its efficiency in early detection of resistance to tebufenozide, topical application on diapausing larvae can thus be considered an appropriate, simple and robust tool for implementing resistance monitoring programmes for tebufenozide.

Dose-mortality curves were established for 12 insecticides administered by topical application to diapausing larvae from a susceptible codling moth strain. Toxicity varied greatly among the insecticides tested. LC50 values ranged from 0.1 mg kg(-1) for fenoxycarb to over 2800 mg kg(-1) for diflubenzuron and indoxacarb. Discriminating dose levels were determined from dose-mortality reference curves for the detection of resistance in field-collected diapausing larvae.

No abstract