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 treatment with 1 of 3 protective treatments as an alternative for chemical fumigation of walnuts for control of postharvest insect populations. The initial disinfestation treatment (0.4% O2 for 6 d) was designed to disinfest walnuts of field populations of navel orangeworm, Amyelois transitella (Walker). The protective treatments were low temperature (10 degrees C) storage, controlled atmosphere (5% O2) storage, and application of the Indianmeal moth granulosis virus, and were designed to prevent establishment of indianmeal moth, Plodia interpunctella (Hubner). The initial disinfestation treatment was effective against laboratory populations of navel orangeworm. Efficacy of protective treatments was determined by exposure to Indianmeal moth population levels far higher than those found in commercial walnut storage facilities. All 3 protective treatments prevented development of damaging Indianmeal moth populations as measured by pheromone trap catches and sample evaluation of the walnuts. No Indianmeal moths were trapped, nor were any seriously damaged walnuts (nuts with obvious damage that rendered the nutmeat less marketable or unmarketable) recovered from either low temperature or controlled 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 (119-793/wk) were trapped from untreated nuts, and 35% of the sampled walnuts showed serious damage. Quality analysis by a commercial laboratory showed that overall walnut quality for all protective treatments was maintained at levels acceptable by industry standards.