Susceptibility of two stored product pests to Metarhizium anisopliae Sorokin fungi based on two bioassay methods

This study was conducted to evaluate the susceptibility of two stored product pests, Tribolium confusum (Col., Tenebrionidae) and Oryzaephilus surinamensis (Col., Silvanidae) treated with two Iranian fungal isolates of Metarhizium anisopliae Sorokin, Saravan (DMEI001) and Nour (DMEI002), based on two bioassay methods, suspension and dry conidia. After mass production of fungal isolates under laboratory conditions (16:8 photoperiods, 28± 1°C, 65±5% R.H) and preparing main suspension, five different conidial concentrations were prepared separately based on the logarithmic distances and then each insect were treated by immersing them in five milliliter of conidial suspensions for five second. In dry conidia bioassay method, to prepare the appropriate dosages, one gm dry conidia was blended with 10 milliliter Tween 80 and then the number of its conidia was calculated. Finally, five concentrations of each isolates were prepared, separately. All experiments were carried out in four replicates and for each replication 20 adult (7-10 days old) of each species were treated, separately. The results showed that in both bioassay methods, Saw-toothed grain beetle was more susceptible to both fungal isolates and Saravan isolate with LD50, 2.37×105 and 5.35×104 in suspension method and 9.5×109 and 8.2×108 conidia per milliliter in dry spore method on red flour beetle and sow-toothed grain beetle, respectively had higher pathogenicity than Nour isolate. In comparison of two bioassay methods, the suspension method had higher efficacy than dry conidia method for both fungal isolates.