Entomopathogenic nematodes- Mode of Infection In the soil environment, infective juveniles of entomopathogenic nematodes (Figure 1.) are always searching for the insect hosts to infect, kill, feed and reproduce. Once the infective juveniles of both Steinernematid (Steinernema spp.) and Heterorhabditid (Heterorhabditis spp.) nematodes locate any larval, pupal or adult stages of their insect host, they will rush to find any easy entry routes/points to enter into the insect host body. As shown in Figure 2, the infective juveniles of both Steinernema spp. and Heterorhabditis spp. generally use natural openings such as mouth, anus and spiracles/breathing pores (usually one pair of spiracles per body segment located laterally along the thorax and abdomen of insects) of their hosts as main points of entry. However, the infective juveniles of only Heterorhabditis spp. can also enter into host’s body by puncturing the inter-segmental membranes of the cuticle (see Figure 2). The infective juveniles that enter via mouth and anus will end up in digestive track (gut) whereas those enter through spiracles will reach in tracheal tubes. However, to kill their host successfully for food and development, the infective juveniles of both Steinernematid and Heterorhabditid nematodes eventually need to penetrate by puncturing digestive track (gut) or tracheal tubules (currently, the process of puncturing is unclear) into insect’s body cavity (an open circulatory system) and release symbiotic bacteria, Xenorhabdus spp. and Photorhabdus spp., respectively from their gut in insect blood generally called hemolymph. In the blood, multiplying nematode-bacterium complex causes septicemia and kill their insect host usually within 48 h after infection.
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