Recent advances in bacterial characterization methodologies have made taxonomic categorization significantly more accurate. Here, we re-evaluated the position of bacterial strains (532 and 652) belonging to the genus Hafnia, isolated from flacherie-diseased silkworms in 1965. Phylogenetic analysis based on the 16S rRNA gene sequences of these strains suggests that they belong to genus Enterobacter. Using multilocus sequence analysis (MLSA), these strains were further classified to MLSA group A, which is a “core” group of Enterobacter containing E. cloacae (the type species of the genus). Although these strains were closely related to E. mori, E. tabaci, and E. asburiae, they also had other MLSA characteristics that distinguished them from these neighboring bacterial species. These data were supported by further biochemical analysis. Thus, it appears that the 532 and 652 strains isolated almost half a century ago belong to genus Enterobacter, and their unique characteristics strongly suggest that they are a novel bacterial species.
We found that artificial diet rearing of the silkworm strain p50 under high humidity was harmful to adult emergence. Specifically, median relative humidity (RH) greater than 74% during the 5th instar induced a high rate of occurrence of naked pupae, which then died without emerging as adults (Experiment 1). To determine the specific stage in which mortality induced, we divided the last instar period into three stages—early, middle, and late—and then subjected the larvae to low (L: 47% median RH) or high (H: 80% median RH) humid conditions. The occurrence of naked pupae decreased not according to the specific stage of the larvae but to the duration of exposure to the “L” condition (Experiment 2). We propose that to maintain p50 strains on an artificial diet, they should be reared in lower humidity more than 2/3 period in the last instar stage.
Ecdysone oxidase (EO) is an enzyme that catalyzes the oxidation of ecdysteroids, the molting steroid hormones in insects. This enzyme may play important roles in the conversion of ecdysteroids to 3-dehydroecdysteroids. In this study, we identified a novel EO, designated bmEO2, from the silkworm, Bombyx mori. A cDNA encoding bmEO2 was cloned by employing the reverse transcriptase-polymerase chain reaction (PCR) technique. The deduced amino acid sequence of bmEO2 showed conserved residues and sequence homology to other known insect EOs and glucose dehydrogenase proteins. Quantitative real-time PCR revealed that the bmEO2 transcript was abundantly present in larval testes of B. mori.
We examined the conditions for setting pheromone traps to collect Bombyx mandarina male moths efficiently. More moths were captured with a higher sex pheromone dose within the range of 0.1-10mg of bombykol. The 1-mg dose of bombykol was the most practical, considering trap exchange frequency and lure cost. Trap heights of 0.3-2.3m had no effect on the number of moths collected.