Pathogenicity of a nuclear polyhedrosis virus of the almond moth, Cadra cautella

Tests were conducted with neonate Cadra cautella larvae to determine the pathogenicity of a nuclear polyhedrosis virus. A bioassay on an agar base diet showed that concentrations of 0.25, 0.50, 2.00, and 4.00 polyhedra/mm² killed 27, 55, 87, and 92% of the test larvae, respectively. A study of the time of death showed that most larvae died on the 9th or 10th day after exposure to 4 polyhedra/mm² at 27°C. When larvae were exposed to 8, 16, 32, and 64 × 10³ polyhedra/g of bran diet, recorded mortalities were 18, 22, 48, and 80%, respectively. All the samples of virus in bran diet which were incubated at various temperatures for 7, 14, and 28 days remained stable at all test conditions except the sample incubated at 42°C for 14 days, and those held at 37° and 42° for 28 days. Larvae of C. cautella, Plodia interpunctella, Ephestia elutella, and Paramyelois transitella placed on a diet with 40 × 10³ polyhedra/g had mortalities of 75, 59, 16, and 4%, respectively. Light and electron microscopical examination of P. interpunctella cadavers showed that they were infected with a multiply occluded nuclear polyhedrosis virus.