Efficacy of multiple biocontrol agents against the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on tomato

Biological control provides an environmentally harmonious and potentially stable management tactic to combat noxious pests such as Bemisia tabaci, notorious for its resistance to synthetic pesticides. Bioassays conducted under control chamber conditions integrating applications of the parasitoid Encarsia formosa, reared for 20 years on Trialeurodes vaporariorum, and the fungus Verticillium lecanii on the third-fourth instar nymphs of B. tabaci on tomato, showed a comparable effect between the parasitoid-fungus combined treatment and the fungus treatment alone (70.7percent vs. 70.4percent). Analysis of our results indicates antagonism between the two biocontrol agents related to the parasitoids' ability to discriminate between infected and healthy B. tabaci nymphs. The parasitoid treatment alone produced 36.3percent mortality, with no mortality in the distilled water controls. The behavioural performance of the parasitoid could have either genetic or environmental causes. Bioassays studying the feeding habit of the imported mirid predator Macrolophus caliginosus (adults) and the indigenous mirid Camptotylus reuteri (nymphs and adults) on eggs, or early second instar nymphs of B. tabaci, and choice preference tests indicated a significant difference in feeding between M. caliginosus and C. reuteri. There was no significant difference in percentage feeding of M. caliginosus on eggs (2.2percent) or second instar nymphs (8.0percent). There was a significant difference in feeding of M. caliginosus adults (18.6percent) when offered eggs and second instars in the same arena compared with eggs or second instars offered separately. These results could be attributed to the biological behaviour of the predator having a type III functional response. Studies with the local C. reuteri species showed no significant difference in adult and nymphal consumption on second instars of B. tabaci compared with nymphs on eggs. However, C. reuteri adults fed less on eggs compared with nymphs. This local predatory species appears to be more efficient than M. caliginosus in feeding on particular stages of B. tabaci without depending on prey density. This is further supported by the low consumption of both adults and nymphs in the choice test (4percent and 2.3percent, respectively) compared with M. caliginosus adults (18.6percent).

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