An alternative set of test to bioassay for bioinsecticides

The development of an assay to determine insecticidal properties for either biological and conventional plant protection products plays an important role on the early screening of potential pathogens or derived toxins candidates. The standard methods for the evaluation it has been by bioassay, especially determination of LD50 or LC 50 requiring the use of relatively large numbers of insects and toxin tests. There are several problems connected with these bioassays: availability of insects and in the right life stage, mass producing the candidate species, preparation, reproducibly and costs relative to intensive manpower. These aspects are really important especially when bio-insectides should be tested against new target eg. invasive species in a new country. We present the results of the use of alternative systems in a screening study of Bacillus thuringensis (Bt) strain as potential pathogen for the Red Palm weevil, Rhynchophorous ferrugineus. We propose the use of different techniques such as growth inhibition, effect of pathogen on total number of hemocytes, ratio of selected hemocytes, espression of HSP 70 protein. In particular this protein is involved in the biochemical pathways response in stressed animals. Tests were carried out against the potential less sensitive stage to have a new predictive parameter for screening the reaction of the host to the pathogen. The preliminary results obtained with the proposed tests allows to enlarge the information of the potential pathogenicity of the entomopathogen bacteria and highlight the potential of this set of tests as screening methods to select new potential entomopathogens or bioinsecticides.