Navel orangeworrns, Amyelois transitella (Walker), completed development in sunburned walnuts late in the growing season, but moths did not emerge until after harvest. Sunburned walnuts were not attractive to ovipositing moths until considerable hull damage occurred. Only sunburned walnuts with undamaged kernels were suitable for larval development. Navel orangeworrn infestation levels up to 38% were recorded in sunburned walnut samples from the San Joaquin Valley, CA. Nut hull tissue damaged by sunburn was not selected over undamaged hull tissue for moth oviposition. Mean kernel temperatures of sunburned walnuts were higher than both undamaged walnuts and ambient air temperature. Premature hullsplit occurred in sunburned walnuts of both early and later maturity varieties. These data suggest that, although sunburned walnuts contribute to the seasonal buildup of navel orangeworms, the late development of navel orangeworms in these nuts reduces the incidence of infestation in hullsplit, new crop nuts.



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