Effect of rainfall on a population of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Abstract

The present study was carried out under artificial rainfall conditions to determine the details of rainfall effect on a DBM population on cabbage. Although most DBM eggs laid on the upper leaf surface were washed off with precipitation of 17.3 mm in 1 h with drops of 2.5 mm in diameter, few eggs laid on the lower surface were washed off. Under the same rain conditions as for the eggs, the falling rate of larvae decreased with advancing larval stadium except for the 1st larval stage. The number of falling larvae increased with increasing treatment time, and the effect reached a ceiling in about 1 h. With increasing time of exposure to hard rain, there occurred a similar increase in the falling rate of DBM larvae. Even after 1 h of steady rainfall, complete removal of the larvae was not achieved. When either the density of droplet was increased or the period of rain was extended, the falling rate for 3rd stadium larvae increased. When droplet diameter increased and the total amount of rainfall remained constant, there was an increase in the number of fallen larvae.