Infection of the European chafer,Amphimallon majalis by Bacillus popilliae: Light and electron microscope observations

Following ingestion of spores of Bacillus popilliae by grubs of the European chafer, Amphimallon majalis, vegetative rods were observed within phagocytic vacuoles of midgut columnar cells prior to establishing primary infection foci in regenerative nidi areas. This resulted in increased activity of regenerative nidi and extrusion of degenerating epithelial cells frequently containing vegetative rods of B. popilliae. Circulating hemocytes adhered to the hemocoelic surface of the basement membrane and formed inflammatory capsules immediately adjacent to the areas of bacterial proliferation. Bacilli in various stages of degradation were observed in membrane-limited vacuoles of both mesenteric epithelial cells and capsular hemocytes. Despite these host defense reactions, some vegetative cells resisted degradation and were successful in traversing the epithelial, basal lamina, and capsular barriers to enter the hemolymph.