Screening entomopathogenic nematode species for management of the woolly apple aphid (Eriosoma lanigerum)

The withdrawal and restriction of certain effective insecticides has led to the woolly apple aphid Eriosoma lanigerum becoming a major pest in apple growing areas across Western Europe. Since a part of the aphid’s life cycle occurs in the soil, application of entompathogenic nematodes (EPN) is considered to be a possible alternative strategy for management of this serious pest. The aim of this study was to evaluate the efficacy of commercially available EPN species (Heterorhabditis bacteriophora, Heterorhabditis megidis, Steinernema carpocapsae, Steinernema feltiae, Steinernema glaseri and Steinernema kraussei). Woolly apple aphids were held individually in a multiwell cell lined with filter paper. Each aphid was exposed to a nematode suspension of 40µl containing approximately 150 infective juveniles of one of the EPN species. Mortality of each aphid was assessed after 3 days. Aphids were dissected and the number of dead and living nematodes inside the insect bodies were counted. The following mortality rates (with Abbott’s correction) were determined for E. lanigerum: 1% with H. bacteriophora, 5% with H. megidis, 43% with S. carpocapsae, -2% with S. feltiae, -4% with S. glaseri and 17% with S. kraussei. Only S. carpocapsae was able to cause significant mortality to the aphids. Addition of the non-ionic surfactant Trend 90 (isodecyl alcohol ethoxylate) to the nematode suspension significantly increased parasitization rates for H. bacteriophora (p < 0.001), S. carpocapsae (p = 0.025), S. feltiae (p < 0.001) and S. kraussei (p < 0.001). Furthermore, the number of EPN individuals found in the aphid bodies was significantly higher for H. bacteriophora (p < 0.001), S. carpocapsae (p = 0.041) and S. kraussei (p < 0.001) when adding Trend 90. We will further examine the influence of several biotic and abiotic factors on the efficacy of the EPN application. In addition, field studies will be performed to monitor the phenology of the woolly apple aphid in Belgian orchards and to examine the control capacity of selected EPN species under field conditions.