Effect of the insect growth regulator novaluron on diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), and its indigenous parasitoids

Research to evaluate effective and selective insecticides through periodic screening is needed to strengthen diamondback moth (DBM) (Plutella xylostella L.) management. The efficacy of the insect growth regulator novaluron on DBM and effects on the parasitoids Diadegma sp. (Hym.: Ichneumonidae), Apanteles sp. (Hym.: Braconidae) and Oomyzus sokolowskii Kurdjumov (Hym.: Eulophidae) were evaluated. Novaluron was compared with the microbial insecticide Bacillus thuringiensis (Bt) var. aizawai, the pyrethroid insecticide λ- cyhalothrin and the organophosphate insecticide profenofos. Two replicated experiments were conducted on head cabbage, Brassica oleracea var. capitata, planted in March and May 2007 at Wonji in the Central Rift Valley of Ethiopia. Infestation by DBM was less with novaluron and Bt compared with other treatments for both planting dates. Infestation with λ-cyhalothrin and profenofos was comparable with the untreated control. Yields were greatest with novaluron and were 80 and 32.5% (12.4 and 7.4 t ha−1) greater than the untreated treatment for the first and second plantings, respectively. Diadegma sp. accounted for 91% of the parasitoid complex observed. Parasitism of DBM by Diadegma sp. ranged between 10 and 43% among treatments. Parasitism was less with λ-cyhalothrin and profenofos compared with other treatments. Owing to its efficacy against DBM and relative safety to its parasitoid, Diadegma sp., novaluron can be used in integrated DBM management for low elevation brassica production in the Central Rift Valley of Ethiopia.

► Infestation by diamondback moth (DBM) was less with novaluron and Bacillus thuringiensis (Bt) compared with λ-cyhalothrin and profenofos.
► Parasitism by the dominant indigenous parasitoid, Diadegma sp., was less with λ-cyhalothrin and profenofos compared with novaluron and Bt.
► Hence, owing to its efficacy against DBM and relative safety to its parasitoid, Diadegma sp., novaluron can be used in integrated DBM management for low elevation brassica production in the Central Rift Valley of Ethiopia.