Effect of intra-hemocoelic injection of Enterobacter sp. NAB3 or B. thuringiensis cells on hemocytes of gypsy moth larvae. (a) 10 μl of PBS, (b) approximately 107 cells of Enterobacter sp. NAB3 or (c) B. thuringiensis (non-sporulated) were introduced into three separate cohorts of 4th-instar larvae (n = 10 each). Representative images of samples from each treatment are shown. To monitor the growth of injected bacteria, hemolymph samples were removed after 24 h and observed by light microscopy at 40×. Hemocytes from uninfected larvae were scattered randomly in the microscope field (a). In contrast, large aggregates of hemocytes were observed in samples from larvae injected with NAB3 (b) and smaller aggregates in samples from larvae injected with B. thuringiensis (c).