COMBINATION OF 2 ENTOMOPATHOGENIC - NEMATODE SPECIES FOR SUPPRESSION OF AN INSECT PEST

Laboratory and greenhouse studies were conducted to determine whether combining 2 entomopathogenic nematode species would result in synergis tic, additive, or antagonistic effect against End-stage larvae of the western spotted cucumber beetle, Diabrotica undecimpunctata undecimpun ctata Mannerheim. After an initial screening of 12 nematode species/st rains, the most efficacious Steinernema and Heterorhabditis and 2 Stei nernema species that were intermediate in effectiveness were selected for further evaluations. In laboratory soil bioassays, the lethal conc entration resulting in 50% mortality (LC(50)) for the most virulent ne matode, Steinernema carpocapsae (Weiser) All strain, was 14.5 infectiv e juveniles followed by 18.4 infective juveniles for Heterorhabditis b acteriophora Poinar NC1 strain, 48.1 infective juveniles for S. riobra vis Cabanillas, Poinar and Raulston Texas strain, and 98.6 IJs for Ste inernema sp. Hanrim strain. Combining 2 of the 4 nematode species at t he LC(25) values always resulted in an additive effect, regardless of the effectiveness of the individual nematode species. In the greenhous e, application of S. carpocapsae, S. riobravis, Steinernema sp., or H. bacteriophora was made alone or in paired combinations at tile rates of 1 x 10(8) and 2.5 x 10(8) infective juveniles/ha against western sp otted cucumber beetle larvae. At both rates, the most efficacious sing le nematode species against the larvae was S. carpocapsae. The combina tion of 2 nematode species showed variable results. Its efficacy range d between as high as the better of the 2 combined species alone and as low as the less effective of the 2 species alone. In addition, the co mbined nematode treatments were always less effective than the most ef ficacious single nematode species, S. carpocapsae. We conclude that no advantage was gained by combining 2 entomopathogenic nematode species against western spotted cucumber beetle larvae.