Histological observations by light and scanning electron microscopy of the Japanese pine sawyer, Monochamus alternatus, infected with the entomopathogenic nematode, Steinernema carpocapsae

Light (LM) and scanning electron microscopy (SEM) were used to study infection of adults and larvae of the Japanese pine sawyer, Monochamus alternatus , by infective juveniles (IJ) of Steinernema carpocapsae (Mexican strain). The IJ entered the alimentary canal of both larvae and adults of M. alternatus via the anus. Entry through spiracles was not observed. Both larvae and adult died within 48 h after infection. SEM revealed the changes in the distribution and reproduction of the symbiotic bacterium, Xenorhabdus nematophila , in the insect body over time. The observations were consistent with the hypothesis that septicaemia was the main cause of insect death. Bacteria grew vigorously and were distributed widely in the insect body as soon as the IJ invaded the insect. Reproduction of the nematode within the insect followed the reproduction of the bacterium throughout the insect body.