Interguild antagonism between biological controls : impact of entomopathogenic nematode application on an aphid predator, Aphidoletes aphidimyza (Diptera : Cecidomyiidae)

This study evaluates the potential of the entomopathogenic nematodes (EPNs) Steinernema carpocapsae, Steinernema feltiae, and Heterorhabditis bacteriophora to cause mortality of an aphid predator, Aphidoletes aphidimyza. In soil-filled Petri dishes, A. aphidimyza adult emergence declined as the EPN infective juvenile (IJ) concentration increased. Percent emergence of adult A. aphidimyza was reduced by H. bacteriophora and S. carpocapsae, but not by S. feltiae, at an IJ concentration approximating a field application rate (25 IJs/cm2). Heterorhabditis bacteriophora, but not S. carpocapsae, reduced emergence of pupae from cocoons following exposure of cocooned A. aphidimyza to IJs in soil. Therefore, A. aphidimyza mortality caused by S. carpocapsae, but not H. bacteriophora, can be reduced depending on the timing of its application relative to A. aphidimyza developmental age. In the greenhouse, application of 2500 S. carpocapsae IJs (∼field rate), 25,000 S. carpocapsae IJs, or 25,000 H. bacteriophora IJs to soil-filled pots (10 cm × 10 cm × 8.5 cm) reduced A. aphidimyza adult emergence. However, the results were not consistent among trials. Aphidoletes aphidimyza adult emergence was further reduced in pots containing wheat (Triticum aestivum), suggesting that the encounter rate between IJs and A. aphidimyza was greater in the presence of roots than in root-free soil. This study shows that an application of S. carpocapsae or H. bacteriophora IJs resulted in significant A. aphidimyza mortality, although only S. carpocapsae displayed potential to affect A. aphidimyza efficacy.