Population density of Plutella xylostella (Lepidoptera: Plutellidae) and its parasitoid Cotesia plutellae (Hymenoptera: Braconidae) on two varieties of cabbage in an urban environment

Abstract

Population density of Plutella xylostella on two cabbage varieties (Kinkei 201 and Shinsei) in an urban environment created different pest loads. A maximum larval density of 9.3 larvae per plant was recorded in Kinkei 201 field. In contrast, the corresponding value was 6.3 larvae per plant in Shinsei field. Shinsei cabbage showed lower larval density of pest but higher parasitism by Cotesia plutellae. Four major parasitoids and two hyperparasitoids were collected and identified during the two year period. No egg parasitoids of the DBM were observed. Comparison of C. plutellae parasitism rates between the two varieties in the field showed a higher parasitism rate on Shinsei cabbage. Parasitoid density peaked on July 13 (4.1 cocoons/plant) in Shinsei and on June 27 (2.3 cocoons/plant) in Kinkei 201. Parasitism of host larvae by C. plutellae was high on Shinsei cabbage in both years and ranged from 40 to 83.3%. Pest density, parasitism rates and rain impact on Kinkei 201 and Shinsei are discussed.