A novel milky disease organism from Australian scarabaeids: Field occurrence, isolation, and infectivity

Abstract

A novel milky disease organism has been found causing disease in Aphodius tasmaniae and other scarabaeid larvae in the field in Australia. The sporangium is exceptionally long, measuring 10.5 × 1.5 μm, with a small central spore, measuring 1.0 × 0.6 μm. The vegetative cell is about half the size of the sporangium. The disease was easily transmitted by injection of spores into the hemocoel, with typically milky symptoms developing in 2–4 weeks. Spores will form in vivo at temperatures down to 12°C. For A. tasmaniae third-instar larvae, the ID 50 by injection was 3 × 10 2 spores/larva, yet no infection resulted when larvae were reared in peat containing up to 10 8 spores/g, i.e., the disease was not successfully transmitted per os. All 10 species of scarabaeids tested were susceptible to the disease when spores were injected; however, all attempts to infect larvae per os were unsuccessful. In vitro culture was also unsuccessful.