PATHOGENICITY OF ENTOMOPATHOGENIC FUNGI AGAINST Sitophilus granarius(L.) (COLEOPTERA: CURCULIONIDAE) UNDER ABIOTIC FACTORS

Abstract

Present bioassays were conducted to determine the effect of temperature and relative humidity (r.h.) on the pathogenicity of two commercially available formulations of entomopathogenic fungi (EPF) i.e. Metarhizium anisopliaeand Beauveria bassianaagainst Sitophilus granarius(L.). Adults of S. granariuswere exposed to three conidial concentrations (1× 108, 1.5× 108 and 2× 108 CFU kg-1of wheat grains) of each EPF at three temperature ranges (25, 30 and 35°C) and relative humidity levels (45, 60 and75%). Pathogenicity was assessed after 7, 14 and 21days(d) and after last count of 21 d all adults were removed from the vials and vials were maintained at same conditions foradditional 60 d to assess the F1adult progeny development. Results showed that efficacy of EPF influenced by temperature, relative humidity, conidial concentration and exposure period. In case of B. bassianapathogenicity was increased with reduced temperature 25°C and moderate r.h. 60% and reached up to 72.5% at higher tested conidial concentration after 21 d of exposure period. For M.anisopliaeoptimum conditions for pathogenicity were moderate temperature (30°C) and r.h. (60%) at which maximum pathogenicity of 64.16% was achieved after 21 d with highest concentration. Regarding progeny production, reduced level of r.h. (45%) significantly suppressed the adult emergence with all tested levels of temperature for both EPFs. However, least numbers of adults were emerged on those abiotic conditions where higher pathogenicity was noticed. Overall results illustrated that both EPF have potential to control S. granariusbut their efficacy highly dependent on abiotic factors and these factors should be seriouslyconsidered when planning an IPM program based on EPF.