The inactivation of Bacillus thuringiensis spores and spores treated with two protectants, one proteinaceous and the other a commercial product, Shade, at wavelengths of the near-ultraviolet and visible spectra and at 254 nm is described. Determination of the inactivating wavelengths may be used to establish an efficient sunlight protective system for B. thuringiensis when used as a microbial insecticide.

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Monochromatic radiation at wavelengths of 290, 300, 310, and 320 nm inactivated occluded nuclear polyhedrosis virus of the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough). Data indicate that all of the wavelengths are capable of causing virus inactivation; much greater fluences are needed for virus inactivation as the wavelength increases.

It was found by using spectrophotometric, spectrofluorometric, and high-pressure liquid chromatography that four subspecies of Bacillus thuringiensis produce coproporphyrin. The porphyrin isomer was identified as coproporphyrin I for B. thuringiensis subsp. kurstaki (HD1). The porphyrin was isolated both from spores and from a variety of spent growth media. The quantity of porphyrin released by each Bacillus subspecies differed. The rank order of porphyrin production follows: B. thuringiensis subsp. kurstaki HD1 > B. thuningiensis subsp. thuringiensis HD27 > B. thuringiensis subsp. thuringiensis HD41 > B. thuringiensis subsp. darmnstadiensis HD199.