Entomopathogenic Nematode‐Mediated Modulation of Metabolism in Caterpillars: A Comprehensive Review and Future Perspectives

ABSTRACT

Among the several factors that govern the success of entomopathogens as environmentally sustainable biological control agents against insect hosts is their ability to modulate certain metabolic activities of infected hosts. Despite the large‐scale use of entomopathogenic nematodes (EPNs) in insect control, our knowledge of their ability to modulate metabolic aspects of infected lepidopteran larvae (caterpillars) is not comprehensive. This review aims to synthesize the current knowledge of the metabolic impacts of EPNs on lepidopteran larvae in an attempt to elucidate host‐EPN/symbiotic bacteria complex interactions. The past and state‐of‐the‐art research achievements that assess the modulation of the total contents of energy reserves (proteins, carbohydrates, and lipids) and the activities of various enzyme systems, including digestive, transaminase, detoxifying, antioxidant, immune, and cholinergic enzymes in EPN‐infected lepidopteran larvae were screened for relevance. The present review revealed a broader metabolic modulation exerted by EPNs, including a decrease in energy reserves and transaminase enzymes while detoxifying and antioxidant enzymes were increased, with variable responses in other enzyme classes. The detoxification reactions and host antioxidative response played a central role in the defensive reaction to EPNs, and that this stress contributed to the death of hosts. The biochemical and molecular mechanisms governing the immune interactions between insect hosts and EPNs were discussed. The role of the insecticidal active substances secreted by the symbiotic bacteria of EPNs ( Xenorhabdus and Photorhabdus ) during reproduction as well as the role of effector proteins excreted/secreted by EPNs themselves independent of their symbiotic bacteria in modulating host metabolism and immunity was also discussed. The interaction between the EPNs and the insect hosts appears to be primarily nutritional. In light of this review, future perspectives and innovations that may aid in harnessing EPNs for sustainable pest management are highlighted.