Entomopathogenic nematodes have been proposed as biological agents for the control of Drosophila suzukii, an invasive pest of small-stone and soft-skinned fruits. Larvae of the fly are susceptible to Steinernema carpocapsae infection but the reaction of immune defenses of the host are unknown. To determine the immune response, larvae were infected with S. carpocapsae and Xenorhabdus nematophila to evaluate the effector mechanisms of both humoral and cellular processes. The symbiont bacteria presented an inhibitory effect on the phenoloxidase cascade with a low level of melanization. Besides, X. nematophila activated the synthesis of putative antimicrobial peptides on the hemolymph of infected larvae. However, those peptides presented a lower antimicrobial activity compared to hemolymph from larvae infected with non-symbiont bacteria. Xenorhabdus nematophila avoided also the phagocytosis response of hemocytes. During in vitro and in vivo assays, S. carpocapsae was not encapsulated by cells, unless the cuticle was damaged with a lipase-treatment. Hemocyte counts confirmed differentiation of lamellocytes in the early phase of infection despite the unrecognition of the nematodes. Both X. nematophila and S. carpocapsae avoided the cellular defenses of D. suzukii larvae and depressed the humoral response. These results confirmed the potential of entomopathogenic nematodes to control D. suzukii.

中文翻译：

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铃木果蝇幼虫对Nematobacterial complex Steinernema carpocapsae-Xenorhabdus nematophila感染的免疫应答。

昆虫病原线虫已被提议作为控制铃木果蝇（Drosophila suzukii）的生物药剂，果蝇是小石头和软皮水果的入侵害虫。苍蝇的幼虫很容易受到Steinernema carpocapsae的感染，但宿主的免疫防御反应尚不清楚。为了确定免疫反应，将幼虫感染了腕果链球菌和嗜线虫杆菌，以评估体液和细胞过程的效应机制。共生细菌对苯酚氧化酶级联具有抑制作用，且黑色素水平低。此外，嗜线虫X.激活了被感染幼虫血淋巴上假定的抗菌肽的合成。然而，与来自感染非共生菌的幼虫的血淋巴相比，这些肽具有较低的抗菌活性。Xenorhabdus nematophila也避免了血细胞的吞噬反应。在体外和体内试验中，除非将表皮用脂肪酶处理破坏，否则囊状链球菌不会被细胞包裹。尽管未识别线虫，血细胞计数仍证实感染初期的层状细胞分化。既X.线虫和S. carpocapsae避免蜂窝防御D. suzukii幼虫并抑制了体液反应。这些结果证实了昆虫病原线虫控制铃木D.的潜力。