Integration of nonchemical, postharvest treatments for control of navel orangeworm (Lepidoptera : Pyralidae) and Indianmeal moth (Lepidoptera : Pyralidae) in walnuts

We propose a treatment strategy combining an initial disinfestation treatme nt with 1 of 3 protective treatments as an alternative for chemical fumigat ion of walnuts for control of postharvest insect populations. The initial d isinfestation treatment (0.4% O-2 for 6 d)was designed to disinfest walnuts of held populations of navel orangeworm, Amyelois transitella (Walker). Th e protective treatments were low temperature (10 degrees C) storage, contro lled atmosphere (5% O-2) storage, and application of the Indianmeal moth gr anulosis virus, and were designed to prevent establishment of Indianmeal mo th, Plodia interpunctella (Hubner). The initial disinfestation treatment wa s effective against laboratory populations of navel orangeworm. Efficacy of protective treatments was determined by exposure to Indianmeal moth popula tion levels far higher than those found in commercial walnut storage facili ties. All 3 protective treatments prevented development of damaging Indianm eal moth populations as measured by pheromone trap catches and sample evalu ation of the walnuts. No Indianmeal moths were trapped, nor were any seriou sly damaged walnuts (nuts with obvious damage that rendered the nutmeat les s marketable or unmarketable) recovered from either low temperature or cont rolled atmosphere storage. Very low numbers of moths (less than or equal to 21/wk) were trapped from walnuts treated with virus, and only 0.2% of the walnuts were seriously damaged. In contrast, large numbers of moths (119-79 3/wk) were trapped from untreated nuts, and 35% of the sampled walnuts show ed serious damage. Quality analysis by a commercial laboratory showed that overall walnut quality for all protective treatments was maintained at leve ls acceptable by industry standards.