Modifications of the hemogram and of the hemocytopoietic tissue of male adults of Locusta migratoria (Orthoptera) after injection of Bacillus thuringiensis

The injection of live Bacillus thuringiensis (with the culture medium) into the hemocoel of male adults of Locusta migratoria results in a significant fall of the number of circulating hemocytes followed 2 days later by a sharp increase of the hemocyte figure. Identical doses of washed live bacteria have the same effect on the hemogram, whereas neither culture medium deprived of the bacteria by filtration nor heatkilled bacteria modify the hemocyte number. Injection of isolated β-exotoxin of B. thuringiensis in nonlethal concentrations remain without effect on the hemogram.Morphological studies show that the injected bacteria are essentially taken up by the reticular (phagocytic) cells of the hemocytopoietic tissue, leading to a necrotic evolution of many of these cells. Necrotic zones are rapidly encapsulated by granular hemocytes.One to two days after the injection, the hemocytopoietic tissue shows signs of considerable hypertrophy: both the polymorphous reticular cells and the maturing blood clusters become notably more numerous.The modifications observed in the hemocytopoietic tissue partly explain the alterations of the hemogram after injection of B. thuringiensis.