SUSCEPTIBILITY OF THE SUMMER FRUIT TORTRIX MOTH, ADOXOPHYES ORANA (LEPIDOPTERA, TORTRICIDAE), TO CHLORPYRIFOS AND STRATEGIES FOR INSECTICIDAL CONTROL IN ORCHARDS

The susceptibility of populations of the summer fruit tortrix moth, Ad oxophyes orana, from apple orchards in Kent, England, to chlorpyrifos was determined in 1992, 1994 and 1995, by topically dosing larvae feed ing on leaves or adults adhered to pheromone trap sticky bases. LD50 v alues (range 6.3 to 23.2 ng chlorpyrifos per individual) for first or second generation males, second generation females or for first genera tion fourth instar larvae collected in the field were significantly gr eater (2-3 fold) for populations from orchards with a long history of treatment with broad-spectrum organophosphorus and other insecticides than for those from untreated orchards (range 1.6 to 8.1 ng chlorpyrif os per individual), though there was considerable variation between si tes and years. Twelve replicated orchard experiments between 1993 and 1995 were used to examine a range of different strategies for insectic idal control. Applications of chlorpyrifos against overwintered larvae feeding in trusses in spring gave, at best, a 75% reduction in larval numbers, insufficient to prevent damage by the subsequent generation in summer. However, two applications of fenoxycarb (one immediately pr e-and one immediately post-blossom of apple cv. Cox) completely preven ted successful subsequent development of the pest, and a single (post- blossom) spray nearly so. The timing of application of chlorpyrifos ag ainst first generation larvae hatching from eggs in June was shown to be critical and currently used methods of spray-timing were unreliable . The effective persistence of chlorpyrifos was short (<7 days). Thoug h good control could be achieved with a single spray, a better strateg y was to apply a series of sprays at 7-day intervals to cover the egg hatch period. Sprays of Bacillus thuringiensis at the same timing inte rvals gave, maximally, an 80% reduction in larval numbers, but usually less: improved control was not achieved by applying a programme of sp rays compared to a single spray, though a novel, more potent, formulat ion was significantly more active. Triazophos was also effective as an egg hatch spray. Sprays of chlorpyrifos or tebufenozide between late September and mid-October 1995 against second or third instar larvae m igrating to overwintering sites before diapause, failed to reduce sign ificantly the numbers of subsequent overwintering larvae or the number s that emerged to feed on blossom trusses in spring.