Ovomermis sinensis parasitism arrests midgut replacement by altering ecdysone and juvenile hormone in Helicoverpa armigera larvae

Serine protease mediates Ovomermis sinensis-inhibited host immune responses by inducing apoptosis: implications for successful parasitism and host mortality

BACKGROUND

Mermithid nematodes are entomopathogens that parasitize and kill insect hosts and are used for biological control. It is widely believed that mermithid nematodes kill their host upon nematode emergence, unlike other parasites that depend on virulence factors. In this study, we disproved this theory by demonstrating that the mermithid nematode Ovomermis sinensis mediates host mortality by serine protease-induced apoptosis.

RESULTS

Successful parasitism of O. sinensis increased with the infection rate, and the inhibition of host immunity by O. sinensis increased with the parasitic load. A serine protease was identified from the host hemolymph. This protease belongs to the trypsin-like serine protease family, which is an apoptosis-inducing serine protease. Specifically, Os-sp was highly expressed only during the parasitic stage and could be induced by host hemocytes and the fat body. Importantly, host immune effectors (melanization, phenoloxidase activity, and encapsulation) were suppressed by the recombinant protein rOs-sp that induced apoptosis of hemocytes and fat body in a dose-dependent manner, which contributes to host death.

CONCLUSION

Serine protease mediates O. sinensis-inhibited host immune responses by inducing apoptosis that is lethal to the insect host. Our findings have broader implications for understanding the mechanism of successful parasitism and killing of host by nematodes. © 2023 Society of Chemical Industry.

Neural mechanisms of parasite-induced summiting behavior in 'zombie' Drosophila

For at least two centuries, scientists have been enthralled by the "zombie" behaviors induced by mind-controlling parasites. Despite this interest, the mechanistic bases of these uncanny processes have remained mostly a mystery. Here, we leverage the Entomophthora muscae-Drosophila melanogaster "zombie fly" system to reveal the mechanistic underpinnings of summit disease, a manipulated behavior evoked by many fungal parasites. Using a high-throughput approach to measure summiting, we discovered that summiting behavior is characterized by a burst of locomotion and requires the host circadian and neurosecretory systems, specifically DN1p circadian neurons, pars intercerebralis to corpora allata projecting (PI-CA) neurons and corpora allata (CA), the latter being solely responsible for juvenile hormone (JH) synthesis and release. Using a machine learning classifier to identify summiting animals in real time, we observed that PI-CA neurons and CA appeared intact in summiting animals, despite invasion of adjacent regions of the "zombie fly" brain by E. muscae cells and extensive host tissue damage in the body cavity. The blood-brain barrier of flies late in their infection was significantly permeabilized, suggesting that factors in the hemolymph may have greater access to the central nervous system during summiting. Metabolomic analysis of hemolymph from summiting flies revealed differential abundance of several compounds compared to non-summiting flies. Transfusing the hemolymph of summiting flies into non-summiting recipients induced a burst of locomotion, demonstrating that factor(s) in the hemolymph likely cause summiting behavior. Altogether, our work reveals a neuro-mechanistic model for summiting wherein fungal cells perturb the fly's hemolymph, activating a neurohormonal pathway linking clock neurons to juvenile hormone production in the CA, ultimately inducing locomotor activity in their host.