Oviposition and Development of the Navel Orangeworm in Relation to Almond Maturation1

Abstract

Under orchard conditions, oviposition by Paramyelois transitella (Walker) begins on maturing almond fruit just prior to initiation of hull-split. After hull-split is complete, half the eggs are laid within the opened area on the inside of the hull or on the exposed shell, the rest on the outside of the hull. Moths preferentially oviposit on previously infested fruit, as compared with uninfested fruit. Infestation develops explosively after dehiscence begins. Most of the larvae hatching during the early stages of hull-split infest the nutmeat directly rather than feeding on the hull. Preventive treatments during this period should be applied before significant hull-split has taken place. Development of the navel orangeworm in new crop fruit in situ was followed by sampling 3 cohorts of dehiscing fruit artificially infested with eggs of a known age. By applying data developed on width of the larval head capsule to these populations, sampled in sequence, development was charted providing estimates of stadial length. First emergence from the new crop occurred in 29 days, in time to cause reinfestation. Fifty % emergence occurred in 42–45 days.