Efficacy of entomopathogenic fungi against the stored-grain pests, Sitophilus granarius L. and S. oryzae L. (Coleoptera: Curculionidae)

Abstract

Efficacy of the five native entomopathogenic fungi (EPFs), Beauveria bassiana, Isaria fumosorosea, Lecanicillium muscarium, Metarhizium anisopliae, and Simplicillium lamellicola, against adults of the stored-grain insect pests, Sitophilus granarius and Sitophilus oryzae (Coleoptera: Curculionidae), was evaluated under laboratory conditions at two different temperatures. Conidial suspensions (1 × 108 conidia ml−1) of the fungi were directly applied to both the pests in Petri dishes (2 ml per dish), using a Potter spray tower. All the dishes were incubated both at 20 and 25 °C in 16 h light/8 h dark and in 75 ± 5% relative humidity (RH). Dead individuals were counted daily, following treatments, for 7 days. Lethal time values (LT50 and LT90) for EPFs were calculated. The results demonstrated that the mortality rates varied according to both the temperature and the tested EPFs. The highest effect among EPFs at (1 × 108 conidia ml−1) concentration on S. granarius at 20 °C at the end of day 7 was showed by I. fumosorosea (92.69%) and M. anisopliae (90.35%), followed by the other EPFs. Similarly, M. anisopliae and I. fumosorosea were the most effective ones with 90.48 and 84.21% mortality rates, respectively, at 25 °C. However, while M. anisopliae (85.68%) showed the highest effect among all the EPFs applied on S. oryzae at 20 °C, B. bassiana with a mortality rate of 93.66% was the most effective one at 25 °C. LT50 values for I. fumosorosea and M. anisopliae were 2.75 and 2.88/days, respectively, and LT90 values were 4.17 and 4.47/days, respectively, at 20 °C for S. oryzae. However, LT50 values for M. anisopliae on S. granarius in both temperatures were the lowest. This study indicated that M. anisopliae and I. fumosorosea had a significant potential as a biological control agent against S. granarius and S. oryzae. Further studies are necessary to evaluate the efficacy of the isolate on the pests under storage conditions.