Efficiency of the Galleria (wax moth) baiting technique for recovering infective stages of entomopathogenic rhabditids (Steinernematidae and Heterorhabditidae) from Sand and soil

Abstract

The eficiency of using Galleria larvae to quantify the numbers of entomopathogenic nematodes in naturally infested soil or in sand was assessed. Most tests were with an undescribed Steinernema sp. isolated from British soil and designated the Nashes isolate. Bioassays consisted of replacing al1 insects, whether dead or alive, with fresh living ones until infections ceased and counting the numbers of nematodes which established in the larvae. Whether using naturally infested soil or sterile sand, consecutive exposures of 36 days or more were required before infections ceased. However, two or three consecutive bioassays over twelve days recovered 75 Oh or more of the nematodes. A number of tests with 10-500 nematodes per Galleria larva showed a highly significant linear relationship between the dose of nematodes applied and the mean number which established in the insects. This applied for steinernematids and heterorhabditids, in sand and soil, for exposures lasting 72-144 h and at 15 or 20 OC. The proportion of the nematodes which could penetrate and establish in the hosts (the regression coefficient) varied and may provide a useful parameter for comparing the efficacy of different nematodes under specified conditions. Up to six consecutive 72 h exposures failed to recover more than 40 O/o of the nematodes applied. Comparison of two strains of S. feltiae (Filipjev) [ = S. bibionis (Bovien)] with the Nashes isolate showed no significant differences in the percent that established in Galleria larvae after 72 h. The optimal temperature for infection and establishment of the Nashes isolate was 15-20 OC. There was no effect on efficiency of recovery if single insects were used with 25 ml of sand or five larvae with 300 ml of sand.