Infectivity of Steinernema feltiae and Heterorhabditis bacteriophora towards first and second stage larvae of the forest cockschafer, Melolontha hippocastani

At high population densities, the forest cockchafer, Melolontha hippocastani is a serious pest insect causing death to trees and seedlings. In the southern Rhine valley of Germany, a new gradation of M. hippocastani has built up since the 1980s. Despite considerable results on the control of grubs with entomopathogenic nematodes (EPN), so far no nematode was identified, which efficiently infect Melolontha spp. We herein report on laboratory assays with H. bacteriophora and S. feltiae, both alone, in combination with one another and with B. brongniartii against the 1st and 2nd instar larvae of M. hippocastani. First instar larvae did not seem to be more susceptible than second instar larvae. None of the nematode, alone or in combination caused high mortality, with H. bacteriophora being a little better than S. feltiae (28 compared to 4 % at 500.000 IJ’s/m²). In conclusion, the nematodes currently available on the German market cannot reach control reported for B. brongniartii (BIPESCO1; 60 % at 1x1010 conidia/m²).