Physicochemical properties affects on different oil formulations on fungus metarhizium anisopliae for control of oryctes elegans

Abstract

Background and Objective: Date palm horned beetle Oryctes elegans Prell. caused serious damage to date palms. Metarhizium anisipliae is suitable for biological control of this pest in Iran. This study was carried out with the bioassay of M. anisipliae in conditions with different vegetable oils formulation, their synergistic and antagonistic effects and the evaluation of the effect of oil formulation on maintaining the germination capacity of fungi at different temperatures. Materials and Methods: The oils used included Canola, Soybeans, Sesame, Corn and odoriferous oils that their physico-chemical characteristics were studied including non-soap [Iodine] index, soap index and viscosity. About 250 mL of each oil were sterilized for 24 h at-20EC. The LC 50 equivalents to 5.69±108 spores/mL of the pathogen were on each oil formulation for inoculating the larvae of O. elegans. Results: The results showed that the highest reduction of the lethal time was observed in Sesame oil formulation and the lowest in odorless oil formulation. All oils formulations had synergistic effects and increased the pathogenicity of M. anisipliae on the larvae of O. elegans the highest and the lowest synergistic effect were recorded for Sesame oil and odorless oil formulations respectively. Only iodine index had strong and negative effects on Synergist indices. Other physicochemical properties (soap index and viscosity) had medium and positive effects on it. The formulation of M. anisipliae with different oils increased its resistance to thermal shocks and thus its germination increased strength compared to control at higher temperatures. So that the reduction rate of M. anisipliae fungus spore germination was lower than control in high temperature. The highest median life expectancy and the hazard rate of M. anisipliae spore germination recorded in Soybean and Sesame oil formulations and the lowest average median life expectancy and the highest hazard rate in odorless oil formulation. The soap index had negatively affected on the gradient reducing spore germination (C w ) but w the non-ionic index (iodine) and viscosity had positively affected on it. Conclusion: According to this study, Sesame and Canola vegetable oils were recommended for formulation of M. anisopliae isolate DEMID 01.