Detailed photostability studies were carried out using purified delta-endotoxin crystals from Bacillus thuringiensis subspecies HD-1 and HD-73. The mechanism and time course of sunlight inactivation was investigated by: (a) monitoring the tryptophan damage in the intact crystals by Raman spectroscopy, (b) amino acid analysis and (c) biological assays using insects. The results demonstrate that, for purified HD-1 or HD-73 crystals, the 300-380 nm range of the solar spectrum is largely responsible for bringing about crystal damage and consequent loss of toxicity. Purified Bacillus thuringiensis crystals that were exposed to fermentation liquor after cell lysis were more quickly degraded by sunlight than were crystals from cells that were lysed in water. This effect is attributed to adsorption of chromophores by crystals exposed to the fermenter liquor and the subsequent ability of these chromophores to act as photosensitizers. The importance of a photosensitization mechanism in crystal degradation was further emphasized by irradiating Bacillus thuringiensis crystals in vacuo. The latter crystals were found to be less damaged (20% tryptophan loss after 24 h irradiation by the solar spectrum) compared with crystals from the same sample irradiated in air (60% (60% tryptophan loss). Other methods of decreasing exposure of the crystals to oxygen, e.g. by using glycerol as a humectant, were also found to be successful in controlling photodamage. The results concerning photodegradation support a photosensitization mechanism involving the presence of exogenous (and possibly endogenous) chromophores which create singlet oxygen species upon irradiation by light.

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Phospholipids of 27 species of insects representing 6 orders and 20 families were examined by DEAE cellulose column chromatography to determine the choline/ethanolamine phosphoglyceride ratios, and by gas chromatography to determine the constituent fatty acids.The phosphorus in the ethanolamine phosphoglycerides accounted for approximately 50% of the total lipid phosphorus in aphids (Homoptera) and in all but one family of Diptera (flies) examined while the phosphorus in the choline phosphoglycerides accounted for only about 25%. Ethanolamine and choline phosphoglycerides were present in approximately equal proportions in one family of Diptera and in the Coleoptera (beetles) examined. In the other insects examined choline phosphoglycerides predominated, ethanolamine phosphoglycerides comprising only about 25-30% of total lipid phosphorus as they do in most mammalian tissues.Diptera in which ethanolamine phosphoglycerides were the major phosphatides were also characterized by high proportions of fatty acids less than 18 carbons long, particularly palmitoleic acid, in the neutral lipids. Aphids are characterized by a preponderance of 14-carbon fatty acids. The evidence suggests that predominance of ethanolamine phosphoglycerides is associated with a preponderance of shorter chain fatty acids in the neutral lipids.Differences also exist between Diptera and other insects in the fatty acid compositions of different phosphatides, particularly with respect to the distribution of 18-carbon acids. The compositions observed in insects that contained large amounts of the choline phosphoglycerides are similar to those found in vertebrates. Similarities in fatty acid composition of the choline phosphoglycerides in such widely divergent organisms suggest that the fatty acids may play a greater role in phospholipid function than has heretofore been demonstrated.

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