Effect of different concentrations of Beauveria bassiana (Balsamo) Vuillemin against corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae)

Abstract

An evaluation of the efficacy of different concentrations of the entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin against the corn leaf aphid, Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae) was carried out at Maejo University Biological Control Technology Learning Center (MJU-BCTLC) from August to October 2015. Ten concentrations of B. bassiana ranging from 1×10¹ to 1×10¹⁰ spores/ml were used in the bioassay under the laboratory and greenhouse conditions.  The laboratory bioassay revealed that all ten concentrations were found pathogenic to R. maidis. The mortality obtained ranged from 43.60% to 85.40%, highest at 85.40% of the concentration of 1×10¹⁰ spores/ml and lowest at 43.60% of the concentration of 1×10³ spores/ml, three days after treatment (DAT). However, the percent mortality values were not significantly different. They decreased with decreasing spore concentrations. Under the greenhouse condition the aphid infestation was at 65 days after sowing (DAS). At the concentrations of 1×10¹⁰, 1×10⁹, 1×10⁸, 1×10⁷, 1×10⁶ spores/ml. The aphid population (5.6, 7.0, 9.8, 11.0 and 19.2 aphids per plant) at 65 DAS were drastically reduced at 72 DAS to 1.2, 3.0, 5.0, 9.4 and 11.2 respectively. In the control and at the concentration of 1×10³, 1×10² and 1×10¹ spores/ml, the mean number of aphid population gradually increased at weekly interval starting from 58 DAS until the end of cropping period. The study showed that the concentration at 1×10¹⁰ spores/ml was most effective to reduce the corn leaf aphid population.