Screening of field performance of entomopathogenic fungi and nematodes against cabbage root flies (Delia radicum l. and d. floralis (fall.); Diptera, Anthomyiidae)

Finnish isolates of Beauveria bassiana (8 isolates), Metarhizium anisopliae (7), Tolypocladium sp. (2), Paecilomyces farinosus (2), P. fumosoroseus (1), Steinernema feltiae (3) and Bacillus thuringiensis ('Muscabac') were tested for efficacy against mixed populations of Delia radicum and D. floralis under field conditions in 1986-90. All pathogens were applied preventatively, the fungi as aqueous conidial or mycelial suspensions, dry conidia or dry mycelial powder. In only two of the nine experiments did B. bassiana or M. anisopliae give some control. In 1986, B. bassiana SF85-2 and Tolypocladium sp. SF85-4 (both at rate 1.2 x 10 9 conidia plant- 1), and 'Muscabac' (25 g 1 −1 , 1 dl plant −1 ) reduced the number of pupae by 80%, 60% and 50%, respectively, as compared with untreated and chemical (isophenphos) controls. In 1990, M. anisopliae SF86-39 at rate 1.6 x 10 9 conidia plant −1 and 1.5 x 10 8 CFU plant −1 and S. feltiae SFS-22 (35000 plant −1 ), increased the yield of cauliflower 2.2, 1.8, and 2.3-fold, respectively, as compared with the untreated control, but these yields were only 19%, 15% and 19% of those of the chemical (diazinon) control. Paecilomyces isolates were ineffective in the 1986 experiment in which they were included. Our results suggest that it is difficult to find efficient control agents among the fungal and nematode species tested for use as biopesticides against cabbage root flies, but that the potential of M. anisopliae against these pests deserves further study.