Invasion Rate and Pattern of Infestation of an Almond Orchard by the Navel Orangeworm 1

Studies indicate that Paramyelois transitella (Walker) is able to invade rapidly an almond orchard where the within-the-orchard source has been removed. This fact was indicated by the presence of eggs deposited on nuts artificially hung in the trees. Complete removal of all old nuts from the orchard insured that oviposition was effected by immigrating moths. The greatest amount of oviposition occurred in the half of the orchard that was adjacent to the more heavily infested surrounding areas. The orchard was invaded in all quarters within 39 days during the spring flight; 61% of the infestation occurred within 12 days. There may be economic advantages to the sanitation practice of cleaning almond orchards of old nuts. At harvest, 4.9% of the nuts from the experimental orchard contained navel orangeworm damaged kernels; an adjacent orchard had 7.9% damaged kernels.