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item Meikle, William

Submitted to: Biocontrol Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2002
Publication Date: 10/22/2002
Citation: Cherry, A., Mercadier, G., Meikle, W.G., Castelo-Branco, M., Schroer, S. 2002. The role of entomopathogens in dbm biological control. Biocontrol Symposium Proceedings.

Interpretive Summary: 1. Problem. Diamondback moth is a cosmopolitan pest of cruciferous crops, which are themselves particularly important to peri-urban agriculture in many countries. Over-use and misapplication of pesticides have caused widespread resistance, leading to higher control costs and more damage. Entomopathogens, in the form of viruses, bacteria, fungi and nematodes, may play an important role in diamondback moth control. Many pathogens can be applied in a manner similar to pesticides, and can be used to treat infestations that have escaped other kinds of biological control. 2. Approach. Recent advances in diamondback moth pathology were extensively reviewed, with particular attention being paid to field application. The relationships and relative virulence of several kinds of viruses were explored. Diamondback moth is attacked by many kinds of fungi, and the literature on the main groups was examined for future potential. B.t., which is a common biopesticide, was reviewed, along with the common groups of pathogenic nematodes 3. Results. Much field work has been done on the use of pathogens against diamondback moth, but in spite of that the acceptance of biopesticides in general has been low over the past decade. Many reasons are given for the lack of adoption, such as short shelf life, slow speed of kill and low specificity. However, because pathogens offer many advantages, such as low probability of resistance and low environmental toxicity, there is clearly an increasing role for biopesticides.

Technical Abstract: 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 it's 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. xylostella 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.