SUSCEPTIBILITY OF THE SUMMER FRUIT TORTRIX MOTH, ADOXOPHYES ORANA (LEPIDOPTERA, TORTRICIDAE), TO CHLORPYRIFOS AND STRATEGIES FOR INSECTICIDAL CONTROL IN ORCHARDS
Jv. Cross, SUSCEPTIBILITY OF THE SUMMER FRUIT TORTRIX MOTH, ADOXOPHYES ORANA (LEPIDOPTERA, TORTRICIDAE), TO CHLORPYRIFOS AND STRATEGIES FOR INSECTICIDAL CONTROL IN ORCHARDS, Annals of Applied Biology, 131(2), 1997, pp. 197-212
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.