Trichogramma chilonis Ishii: A potential biological control agent of Crocidolomia pavonana in Samoa

Abstract

Crocidolomia pavonana F. (Lepidoptera: Crambidae) is a major pest of Brassica crops in tropical and sub-tropical regions of Africa, Asia and the Pacific. There are no previous reports of effective natural enemies of the pest across this range but in Samoa an arrhenotokous population of the generalist egg parasitoid Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) frequently attacks it. This is the first record of T. chilonis in Samoa. A three-year field recruitment study showed that although C. pavonana eggs occurred at all times of the year, their abundance was greatest during drier periods. Parasitism of C. pavonana egg masses by T. chilonis was variable (0–87% of egg masses attacked) but the parasitoid was recovered from eggs collected at all times of the year and it is well established in the major Brassica growing regions of the island of Upolu. When partial lifetables were constructed for C. pavonana, the rate of egg disappearance (likely due to predation and the physical effects of rainfall) ranged from 0 to 0.839 and the marginal rate of mortality due to T. chilonis ranged from 0 to 0.474. When it was present, T. chilonis was the major mortality factor affecting C. pavonana eggs in all but one of the recruitment studies. The historical problems surrounding the identity and species status of T. chilonis are discussed and its host range and distribution in the Asia-Pacific region is reviewed briefly. Finally, the potential of this population of T. chilonis for development as a biological control agent of C. pavonana is considered.