Abstract
Apple orchardists in Twyford, Hawke’s Bay, have reported increased fruit damage by leafrollers for several years. Of the three pest species present in this area, Planotortrix octo (greenheaded leafroller), is the main species found on fruit. First instar P. octo larvae were screened for resistance by a direct spray test using a Potter tower. Dosage-mortality responses for the offspring of wild-wild pairs from three orchards showed a 7-32 fold resistance to azinphos-methyl compared with larvae from a susceptible laboratory colony. P. octo larvae from one of the above and 16 further orchards were sprayed with a single diagnostic dosage (LD 99 for the susceptible strain). Resistance was found at 17 of 19 sites covering approximately 1000 ha. A resistance management strategy, using pheromone mating disruption, is being implemented.
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