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New Zealand Plant Protection 69 (2016): 325

Detrimental impact of insecticide sprays on Trichogramma chilonis parasitism of Crocidolomia pavonana eggs in Samoa

S. Fangupo, M.J. Furlong and R. Kant

ABSTRACT

Crocidolomia pavonana F. (Lepidoptera: Crambidae) is a major pest of brassica crops in the Pacific and other tropical and sub-tropical parts of the world. In Samoa, farmers use various insecticides against C. pavonana for the production of Chinese cabbage. A recent study found that a local population of Trichogramma chilonis (Hymenoptera: Trichogrammattidae) successfully parasitises eggs of C. pavonana. This study determined the effects of key insecticides on T. chilonis parasitism in field trials. It showed that the number C. pavonana eggs on Chinese cabbage was significantly reduced after applications of Attack™ (p=0.004) Orthene™ (p=0.001) and Dipel™ (p=0.001) but not after Entrust™ (p=0.268). Negative effects of insecticides were observed on the parasitism rate of T. chilonis and C. pavonana egg masses, which were more likely to be only partially parasitized after an insecticide application. Attack™ and Entrust™ adversely affected T. chilonis parasitism rates of C. pavonana eggs. However, of the insecticides tested Dipel™ reduced T. chilonis parasitism the least. This study suggests that Dipel™ could be considered for inclusion in IPM programmes that depend on T. chilonis parasitism of C. pavonana.

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