Laboratory studies on the mating behavior of the navel orangeworm, Paramyelois transitella (Walker) showed that mating is stimulated by a twilight period. Multiple mating is not uncommon, but males tend to mate more readily with virgin females. Oviposition begins on the second day after mating and reaches a peak on the eighth day.

Studies on black light attraction in the greenhouse showed a diminishing percentage of trapped females in relation to males as the distance from the trap was increased. The heavier bodied females are poorer flyers than the males. This may explain the high ratio of males to females captured in black lights in the field.

Black lights in walnut orchards captured numerous navel orangeworm adults and dissection of the females showed that the majority were in the early to mid stage of reproductive maturity. A method of classifying the females into reproductive age groups was developed in the laboratory using the physiological condition of the females as a criterion. Multiple mating in the field increased as the season progressed and coincided with the periods of highest adult activity.

The data from these studies indicate that black lights are a valuable indicator of navel orangeworm field activity. The mating and oviposition behavior studies provide information that is necessary if a program of control by sterile males is contemplated.