Browsing by Author "Stephan, D."

Two emulsions and two water-based-formulations of freeze dried submerged spores of Metarhizium anisopliae var. acridum (Metch.) Sorokin ( isolate IMI 330189) were compared with aerial conidia ( GREEN MUSCLETM) for their efficacy against Hieroglyphus daganensis (Krauss) and Locusta migratoria ( R. & F.). The field experiments were conducted in East Niger on H. daganensis whereas the laboratory investigations were carried out in Germany using L. migratoria. In the fields, all formulations were applied on one hectare plots using ULV application techniques. Direct and residual spray effects were assessed. In all cases there were highly significant ( p < 0.001) differences between formulations as regards to total mortalities and median survival times (MST). In both direct and spray residue effect assessments, aerial conidia formulated in diesel oil showed over 95% mortality with significantly shorter MST ( 3 to 8 days) under field conditions. These were followed by emulsions of submerged spores, which resulted in a mortality ranging from 56 to 92% ( MST = 8 to 16 days) for the direct spray and 90 to 97% ( MST = 7 to 12 days) for spray residue effect assessments. Experiments in the laboratory positively confirmed these results. There were no apparent differences between water-based formulations and the control with respect to mortality and MST. These results emphasize the importance of employing oil carriers to protect spores from environmental stress and thus enhance efficacy. The study also demonstrated the importance of secondary spore pick up from the spray residues. Spores in all formulations persisted over five days and caused mortalities ranging from 62 to 100% on healthy grasshoppers exposed to the spray residue from treated vegetation. The results of this research suggest that emulsions may be an effective option to improve efficacy of submerged spores for ultra low volume application under Sahelian conditions.

Currently, mycopesticide development for locust and grasshopper control depends on aerial conidia or submerged spores of entomopathogenic fungi. In Our Study, the production of submerged conidia of Metarhizium anisopliae var. acridum (IMI 330189) was investigated in a liquid medium containing 3% biomalt and 1% yeast extract (BH-medium). The effects of freeze and spray drying techniques Oil the quality of submerged conidia were determined. The influence of different additives on the viability of fresh Submerged conidia and their suitability for oil flowable concentrate formulation development was assessed. In a BH medium maintained at 180 rev min(-1), at 30 degreesC for 72 h, IMI 330189 produced a green pigmented biomass Of Submerged conidia whereas in Adamek medium it produced a yellowish biomass of submerged spores. The spore concentration was high in both media; however, the size of the spores produced in the BH medium was significantly lower than those produced in Adamek medium (P<0.001). Submerged conidia can be effectively dried using either freeze or spray drying techniques. The viability and speed of germination were significantly affected by the drying and pulverizing process (P<0.001). The initial viability was significantly higher for spray-dried Submerged conidia than for freeze-dried spores. pulverizing of freeze-dried Submerged conidia reduced the speed of germination and the viability by 63-95%. Dried Submerged conidia can be stored over 45 wk at low temperatures (<10degrees) Without suffering a significant loss in viability. Furthermore, we have identified carriers that Lire suitable for oil flowable concentrate formulation development.

The efficacy of 13 isolates of entomopathogenic fungi belonging to Beauveria, Metarhizium or Paecilomyces spp. was assessed against Sitophilus zeamais (Coleoptera: Curculionidae) and Prostephanus truncatus (Coleoptera: Bostrichidae) using a total immersion bioassay technique in the laboratory. Fungi were applied at concentrations of 1 x 10(7) and 1 x 10(8) conidia mL(-1) for P truncatus and S. zeamais, respectively. All isolates tested were virulent to P truncatus (98-100% mortality, and median survival time (MST) ranged from 2.85-4.05 days). Metarhizium anisophae and B. bassiana were also virulent to S. zeamais (92-100% mortality, MST ranged from 3.58-6.28 days). The isolate of Paecilomyces sp.. was found to be the least virulent against S. zeamais, causing only 26.32 +/- 4.29% mortality with MST of 10.38 +/- 0.29 days. P truncatus proved more susceptible to the entomopathogenic fungi tested than S. zeamais. One M. anisophae (PPRC-EE) and three B. bassiana isolates (PPRC-HH, PPRC-9609 and PPRC-9614) were selected for further study and dose-mortality relationships were assessed on S. zeamais. The tested concentrations: ranged from 1 x 10(4)-1 x 10(7) conidia mL(-1). M. anisopliae (PPRC-EE) showed the lowest LC50 (3.39 x 10(5) conidia mL(-1)) followed by B. bassiana PPRC-HH (2.04 x 10(6) conidia mL(-1)). PPRC-9609 and PPRC-9614, showed slight differences in LC50 but not at LC90. The results revealed the higher potency of M. anisophae as compared with the B. bassiana isolates tested. The study suggests that the use of entomopathogenic fungi may hold promise as an alternative method to control pests of stored products in Ethiopia.