SEM of terminal tooth and basal plate of Heterorhabditis bacteriophora D1. The advantages of cuticular penetration are not just that it enables an additional route of entry, but because for some insects this is the only route. For example, some insects have small diameter spiracles which preclude entry and often the mouth and anus is too tightly closed to allow entry. Scarabaeid beetles have sieve plates covering their spiracles. Moreover, these beetles defecate so frequently that most nematodes which enter the anus are pushed out again.
Many beetles are also able to push nematodes away from the mouthparts with their front legs.
In the case of the blowfly larvae, invasion of the haemocoel via the gut, is accompanied by introduction of larval gut bacteria. Growth of these bacteria in the haemocoel precludes successful parasitism. Consequently, the tooth structure enable greater infectivity of insect larvae by Heterorhabditis spp. SEM showing empty sheaths on larval cuticle left after penetration of 3rd stage Lucilla cuprina larvae by infective juveniles of Heterorhabditis bacteriophora D1. Xenorhabdus from the insect cadaver associate with the foregut of daughter nematodes prior to release.