MICRODISTRIBUTION OF EGGS OF DIAMONDBACK MOTH, PLUTELLA-XYLOSTELLA, ON INTACT AND INJURED CABBAGE PLANTLETS

Experiments were performed outdoors on 2 to 24. December 1991 in Miyazaki, southern Japan. Four cabbage (cultivar: Kinshun) plantlets and 4 or 5 pairs of diamondback moths, Plutella xylostella, were placed in 14 polyester-gauze cages (400 x 400 x 400 mm) to observe where eggs were laid on the cabbage plantlets. Two plantlets in each cage were injured. Injured plantlets had feeding traces made earlier by diamondback moth larvae; the other plantlets were perfectly intact. When two types of plantlets are available to diamondback moths, the moths lay more eggs on injured plantlets than on intact ones. When moths laid eggs on intact cabbages, they laid most eggs on the stem and less than 10% on leaves. However, in injured plantlets, about 70% of eggs were laid on leaves. Eggs were laid on or near the feeding traces, or were attached to threads left by feeding larvae. This suggests that injured cabbage plants are targeted for attack by ovipositing female diamondback moths.