Abstract
Seasonal incidences of Plutella xylostella, diamondback moth (DBM) and its associated natural enemies were investigated in two agro-ecological zones of the major crucifer growing areas of Kenya in 2005 and 2006. DBM larvae and pupae were collected from the cabbage and kale crops grown in farmers’ field and maintained in the laboratory for the emergence of parasitoid or DBM. Four larval, one larval-pupal and one pupal parasitoid species were recorded from DBM. The parasitoids recovered wereDiadegma semiclausum, Diadegma mollipla, Itoplectis spp., Cotesia plutellae, Apanteles spp., Oomyzus sokolowskii and Brachymeria species. D. semiclausum was the most dominant species throughout with highest parasitism rates of over 70% recorded in the highlands. C. plutellae, Apanteles and Brachymeria were recovered from mid-altitude semi-arid areas. Generally, parasitism was significantly higher onBrassica oleracea var. capitata. D. semiclausum displaced the indigenous parasitoids from B. oleracea var. capitata. Key words: Brassica oleracea, parasitoids, diamondback moth, seasons, agro-ecological zones.
Highlights
Diamondback moth (DBM) Plutella xylostella Linnaeus is the most important pest of cultivated crucifers worldwide (Talekar and Shelton, 1993)
D. semiclausum has successfully established and it is providing excellent control of DBM (Löhr et al, 2007). This has resulted in reducing insecticide application by farmers, while others have stopped spraying against DBM altogether in the highland areas where D. semiclausum was released
The highest mean of 3.6 and 2.0 DBM/plant was recorded during the hot dry season in 2005 in Kinangop and Naro Moru, respectively, while the lowest during the short rains (0.24 DBM/plant) and cold dry season (0.27 DBM/plant) in Naro Moru and Kinangop, respectively
Summary
Diamondback moth (DBM) Plutella xylostella Linnaeus is the most important pest of cultivated crucifers worldwide (Talekar and Shelton, 1993). The pest has developed resistance to most chemical and bacterial insecticides (Kibata, 1996).In one of the recent classical biological control efforts, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae) was imported from Taiwan and released in the highland areas of Kenya. D. semiclausum has successfully established and it is providing excellent control of DBM (Löhr et al, 2007). This has resulted in reducing insecticide application by farmers, while others have stopped spraying against DBM altogether in the highland areas where D. semiclausum was released. C. plutellae has not established in the mid-altitude semi arid areas, 2 years after the release since very few individuals were recovered.
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