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Open AccessArticle

Host Immunosuppression Induced by Steinernema feltiae, an Entomopathogenic Nematode, through Inhibition of Eicosanoid Biosynthesis

1
Department of Plant Medicals, Andong National University, Andong 36729, Korea
2
School of Environmental Ecology and Tourism, Kyungpook National University, Sangju 37224, Korea
*
Author to whom correspondence should be addressed.
Insects 2020, 11(1), 33; https://doi.org/10.3390/insects11010033
Received: 10 December 2019 / Revised: 27 December 2019 / Accepted: 28 December 2019 / Published: 31 December 2019
(This article belongs to the Special Issue Insects, Nematodes and Their Symbiotic Bacteria)
Steinernema feltiae K1 (Filipjev) (Nematode: Steinernematidae), an entomopathogenic nematode, was isolated and identified based on its morphological and molecular diagnostic characteristics. Its infective juveniles (IJs) were highly pathogenic to three lepidopteran (LC50 = 23.7–25.0 IJs/larva) and one coleopteran (LC50 = 39.3 IJs/larva) insect species. Infected larvae of the diamondback moth, Plutella xylostella (L.) (Insecta: Lepidoptera), exhibited significant reduction in phospholipase A2 (PLA2) activity in their plasma. The decrease of PLA2 activity was followed by significant septicemia of the larvae infected with S. feltiae. Insecticidal activity induced by S. feltiae was explained by significant immunosuppression in cellular immune responses measured by hemocyte nodule formation and total hemocyte count (THC). Although S. feltiae infection suppressed nodule formation and THC in the larvae, an addition of arachidonic acid (AA, a catalytic product of PLA2) rescued these larvae from fatal immunosuppression. In contrast, an addition of dexamethasone (a specific PLA2 inhibitor) enhanced the nematode’s pathogenicity in a dose-dependent manner. To discriminate the immunosuppressive activity of a symbiotic bacterium (Xenorhabdus bovienii (Proteobacteria: Enterobacterales)) from the nematode, kanamycin was applied to after nematode infection. It significantly inhibited the bacterial growth in the hemolymph. Compared to nematode treatment alone, the addition of antibiotics to nematode infection partially rescued the immunosuppression measured by phenol oxidase activity. Consequently, treatment with antibiotics significantly rescued the larvae from the insecticidal activity of S. feltiae. These results suggest that immunosuppression induced by infection of S. feltiae depends on its symbiotic bacteria by inhibiting eicosanoid biosynthesis, resulting in significant insect mortality. However, the addition of antibiotics or AA could not completely rescue the virulence of the nematode, suggesting that the nematode itself also plays a role in its insecticidal activity. View Full-Text
Keywords: Steinernema feltiae; eicosanoids; PLA2; Plutella xylostella; immunosuppression Steinernema feltiae; eicosanoids; PLA2; Plutella xylostella; immunosuppression
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MDPI and ACS Style

Chandra Roy, M.; Lee, D.; Kim, Y. Host Immunosuppression Induced by Steinernema feltiae, an Entomopathogenic Nematode, through Inhibition of Eicosanoid Biosynthesis. Insects 2020, 11, 33.

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