A SEARCH OF MICROBES PATHOGENIC FOR DIFFICULT-TO-CONTROL INSECT PESTS

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(1) Gene sequence analysis revealed that the Cry proteins of the five Lepidoptera-specific Bacillus thuringiensis strains, that belong to the three H serovars (fukuokaensis, sotto, and galleriae) and produce spherical parasporal inclusions, are of the single category, a novel class belonging to the Cry9 delta-endotoxin.(2) Of 1713 Japanese isolates of Bacillus thuringiensis, 609 (35.5%) exhibited high larvicidal activity against the diamondback moth, Plutella xylostella. Of these toxic isolates, 605 belonged to the H serotypes 1-10. When five selected highly toxic isolates, belonging to four H serovars (sumiyoshiensis, 2 isolates ; fukuokaensis, 1 ; canadensis 1 ; morrisoni, 1), were examined for their delta-endotoxins, the four isolates, excluding the morrisoni isolate, were assigned to the Cry9D-producing strains.(3) Isolation experiments failed to recover Bacillus thuringiensis from soils and floral samples collected in the coastal area of the L_tzow-Holm Bay of the Antarctica sub-continent.(4) Characterization of the microsporidians, isolated from diseased larvae of the silkworm (Bombyx mori) in Brazilian sericultural farms, revealed that (i) the isolates with large- to middle-sized spores belong to the genus Nosema, but differ from the species Nosema bombycis, and (ii) the isolates with small-sized spores belong to the genus Pleistophora.