In 1998, population densities of the obliquebanded leafroller (OBLR) increased dramatically in pistachio orchards in California's Central Valley. A two-year population dynamic study was begun to determine OBLR economic damage and levels of natural enemies. Insecticide treated and "organic' orchards were monitored. Results showed 3-4 OBLR generations, with peak population densities in July. "Strike" counts averaged as high as 120 per 2 minute period in treated fields. Damage to the pistachio nut cluster is low because OBLR larvae greatly preferred pistachio leaves. In both treated and untreated orchards, OBLR densities increased from May through June, after which a complex of parasitoids suppressed OBLR populations in August and September. Parasitoids collected included Macrocentrus iridescens, Spilochalcis sp., Scambus sp., and a tachinid fly. Macrocentrus iridescens accounted for the greatest parasitism levels throughout the season. Parasitism was as high as 15% in the first OBLR generation and increased to >90% by the last OBLR generation in September. Data are used to question whether OBLR and natural enemies originate from inside the orchard or move into the block from alternate hosts elsewhere. Control efforts are currently directed at mass-production of Macrocentrus for inoculative release.
Species 1: Lepidoptera Tortricidae Choristoneura rosaceana (obliquebanded leafroller)
Species 2: Hymenoptera Braconidae Macrocentrus irridescens
Keywords: biological control, orcahrd IPM, population dynamics
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