The role of entomopathogens in DBM biological control

The major groups of entomopathogens that include taxa with pathogenicity to Plutella xylostella are discussed. Among the viruses, several of the Autographa californica MNPV related viruses with wide host ranges, exhibit variable virulence to P. xylostella larvae. At least two of these viruses have been marketed for control of a range of pests including P. xylostella. The recently isolated PxMNPV, also related to AcalMNPV, is very significantly more virulent to P. xylostella than others in the same family. The highly specific P. xylostella granulovirus, previously dismissed because of its environmental sensitivity, is being evaluated in E. Africa where market forces are encouraging biopesticide use on export crops destined for the EU. Of the fungal Hyphomycete species infective to P. xylostella, the commercial product Mycotrol® based on Beauveria bassiana strain GHA has been shown to be effective in the field and the Entomophthoralean species Zoophthora radicans shows promise when used in autodissemination traps, despite problems of persistence. Bacillus thuringiensis continues to be the dominant pathogen used inundatively against P. xylostella, with most commercial products based on the Bt kurstaki subspecies, although Bt aizawai has been used where resistance to Bt kurstaki exists. Entomopathogenic nematodes in the genera Steinernema and Heterorhabditis penetrate all P. xylostella instars, as well as pupae and adults although there is variation in the efficacy of different isolates. Their field use is limited by abiotic factors but spraying at dusk and the use of UV protectants and desiccation protective formulations improves efficacy. Vairimorpha imperfecta is a highly virulent microsporidian pathogen of P. xylostella with potential as a biocontrol agent. However, it also leads to deficiencies in offspring of Trichogramma chilonis that parasitize infected larvae. While several pathogens infective to P. xylostelle now are under commercial development, Bt constitutes the most significant control option. In common with most entomopathogens destined for inundative field application, development of suitable formulation and dissemination technologies remains an over-riding priority if the other pathogens are to gain a market share. (Résumé d'auteur)