Abstract
Life tables were constructed for the diamondback moth, Plutella xylostella living in a broccoli field in Okayama in June, September and October 1989. Four plots were established to evaluate the role of natural enemies and the effect of rainfall on the survival: (1) All natural enemies and rainfall excluded by net and plastic roof; (2) Rainfall excluded by plastic roof; (3) Ground fauna excluded by tangle-foot coated fence; and (4) Control plot. One third to one half of individuals disappeared in the early immature stages. Since the mortality rate was lower in the plots with no rainfall, wash-off of eggs and larvae by rain and drowning of young larvae after rain are considered to be the major mortality factors. Water sprays also washed eggs and larvae off broccoli leaves. The percentage parasitism by the larval parasitoid, Apanteles plutellae, and the pupal parasitoids, Diadromus subtilicornis and Tetrastichus sokolowskii, was high in September. Temperatures of more than 30°C tended to delay development, and reduced the survival of immature stages and the fecundity of females. When the diamondback moth was fed on the wild cruciferous weed Capsella bursa-pastoris, its reproductive ability was lower than that when feeding on crops.
