Caracterisation D’isolats Locaux De Metarhizium Spp, Champignon Entomopathogene De Cosmopolites Sordidus Germar, Isoles Des Bananeraies En Cote d’Ivoire

Chemical insecticides have been commonly used against the black weevil, Cosmopolites sordidus, in banana plantations which caused huge economic and agricultural losses. Despite their benefits, pesticides can be hazardous to both humans and the environment. Intensive research in substituting chemical insecticides with biological control agents have been driven. The biological and molecular characteristics of ten strains of Metarhizium spp, isolated from dead weevils, collected in banana plantation in Côte d'Ivoire were studied. The study aims to identify the species of Metarhizium sp. The biological and molecular characteristics namely: length and width of the spores, colour of aerial mycelium as well as its variation over time, colour on the setback of the box, production of the diffusible pigment and the analysis of the region ITS (Internal Transcribed Spacer) were evaluated. The colonies presented at first a flat white mycelium cottony or fluffy appearance on which the spores formed small islets. After 21 days of incubation at 32°C. in the dark, the mycelium takes on the periphery a greenish coloration with a powdery appearance. The relief is fairly flat. The spores are ellipsoid in shape of 3 μm in length and 1 μm. The amplification by ITS-DNA PCR generated a specific fragment of 550 bp. The analysis of the ITS region of the sequences of these ten (10) isolates showed maximal correspondence with different strains of M. anisopliae and Metarhizium pinghaense.

Effet cytotoxique in vitro et chez l'insecte hôte des destruxines, toxines cyclodepsipeptidiques produites par le champignon entomopathogène Metarhizium anisopliae

The cytotoxic effect of the cyclodepsipeptide mycotoxins of the group of destruxins (DA, DB, DE) has been investigated in the insect host, Galleria mellonella, and in invertebrate cell cultures, mainly at the ultrastructural level. The strong effect of DE is characterized by changes in the morphology of the cells, and the development of structural alterations at the nuclear and cytoplasmic levels. The major lesions observed even at low doses consist in a pycnotic evolution of the nucleus and a degradation of mitochondria, while the rough endoplasmic reticulum and the ribosomes are also impaired. In the host, the main organs and tissues attacked by DE are the midgut, the malpighian tubules, and the circulating hemocytes. A comparative study of the effect of DE, DA, and DB has revealed a specificity in the cytotoxic action of these compounds. The following classification has been observed in the efficiency of the molecules: DE > DA > DB. These results allow a better understanding of the role of peptidic mycotoxins in the pathogenesis of fungal infections. They also reveal similarities with the action of other mycotoxins, and constitute a valuable foundation for studies on the molecular aspects of the mechanism of action of destruxins.Key words: mycotoxin, destruxin, mode of action, cytotoxic effect, in vitro toxicity.