Laboratory screening for virulent entomopathogenic nematodes (Heterorhabditis bacteriophora and Steinernema yirgalemense) and fungi (Metarhizium anisopliae and Beauveria bassiana) and assessment of possible synergistic effects of combined use against grubs of the barley chafer Coptognathus curtipennis

Abstract

Abstract The barley chafer grub, Coptognathus curtipennis, is an important field pest of barley, wheat and linseed seedlings at Tikur Inchini district of theWest Shewa zone of Ethiopia in Ormoia regional state. Two entomopathogenic nematodes (EPN; Heterorhabditis bacteriophora and Steinernema yirgalemense, strains ANEPN21, ANEPN22, respectively) and three entomopathogenic fungal isolates of Metarhizium anisopliae (MM, EE and PPRC66) were compared separately at different rates of concentration for their effect against C. curtipennis in laboratory bioassays. Heterorhabditis bacteriophora and M. anisopliae isolate MM were found to be the most pathogenic to C. curtipennis at 1000 infective juveniles (IJ)/grub and 108 conidia (g soil)–1 concentration, causing 88.7% and 88.6% mortality, respectively, after 3-4 weeks exposure. These two most effective entomopathogens were further tested against the same insect in simultaneous and sequential combination with each other. Insect larvae were exposed to optimal concentration of H. bacteriophora and M. anisopliae isolate MM, which caused 50% larval mortality, i.e., 380 IJ/grub and 1.7 × 107 conidia (g soil)–1, respectively, as observed in the first experiments. The combined application increased larval mortality in an additive and synergistic manner. To achieve a strong synergistic effect, larva had to be exposed to M. anisopliae isolate MM 3 weeks before the addition of nematodes. The result of the whole experiment suggests that the damage caused by barley chafer grub can be controlled or managed by applying EPN and/or fungi. Furthermore, the combined use of M. anisopliae with nematodes may offer an integrated approach to increase the efficacy of EPN for C. curtipennis control and perhaps other insect pests.