Larvicidal Activity of the Symbiotic BacteriumXenorhabdus japonicusfrom the Entomopathogenic NematodeSteinernema kushidaiagainstAnomala cuprea(Coleoptera:Scarabaeidae)

Abstract

The entomopathogenicity of the symbiotic bacteriumXenorhabdus japonicusand the nematodeSteinernema kushidaiwas determined. Phase I and IIX. japonicuswere cultured on an artificial medium and inoculated into the test insect or established into axenicS. kushidaipopulations. When 100, 1000, or 10,000 bacterial cells of phase I or II were directly injected into the hemocoels of 3rd instar cupreous chafer,Anomala cuprea,both phases in the late log period killed 100% of the larvae by the 2nd day postinoculation. However, both phases in the stationary period were less pathogenic with cupreous chafer mortality <20 and 80% at 100 and 1000 bacterial cells/larva, respectively.In vitrostudies showed that axenicS. kushidaiprovided with phase I or II symbionts grew well and produced equal numbers of progeny on a dog food medium, but nematodes with no symbionts did not grow at all. Pig liver extracts added as a dietary supplement to the dog food medium completely restored growth and progeny production of the nematode with no bacterial cells. Studies were conducted with infective juveniles (IJs) harboring phase I or II or no symbionts that were applied against 3rd instar cupreous chafer larvae in compost or injected directly into their hemocoels. In the compost study, IJs harboring phase I killed 100% within 10 days. IJs with phase II or no symbionts caused low mortality of the cupreous chafer larvae at 10 days (<20%). In the intrahemocoelic injection study, IJs harboring phase I resulted in 60% larval mortality at five nematodes/larva, and as the number of IJs injected increased, significantly higher larval mortality was obtained.