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.

Artificial release of marked adult Diaphorina citri, the insect vector of citrus greening disease, was performed in July 2007 (10,000 adults released, experiment 1) and October 2008 (1,000 adults released, experiment 2) to determine the association of the dispersal pattern with disease invasion risk. During the experimental periods, in experiment 1, the mean dispersal distances from the release point were 5-6 m and in experiment 2 they were 6-12 m. Further examination of the relationship between dispersal distance and season is needed. The number of released D. citri declined with increasing distance from the release point and did not change markedly with time. The center of distribution moved little during the experimental period. These results suggest that the adult D. citri barely moved once they had colonized a host plant within a few days after their release. Our results also suggest that the released D. citri moved with the wind. The diffusion coefficient was estimated at 7.23 from experiment 1, but random diffusion might be a poor descriptor of the dispersal of adult D. citri.

Pesticide (six insecticides and 16 acaricides) susceptibility of populations of N. californicus (4 populations) and N. womersleyi (5 populations) was investigated to test the hypothesis that the recent species replacement between these two species was due to a change in pesticides used in orchards combined with a differential susceptibility of the two species to one or more of the new pesticides. Although the present results cannot provide a clear conclusion regarding factors responsible for the change in dominant phytoseiid, it was suggested, at this point, that none of the pesticides examined here seemed to have a decisive influence on the replacement of N. womersleyi by N. californicus.

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