Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
J Invertebr Pathol. 2020 Jul;174:107428. doi: 10.1016/j.jip.2020.107428. Epub 2020 Jun 15.
An entomopathogenic nematode, Steinernema feltiae K1, exhibits pathogenicity in various insect hosts, however, its virulence among the target insect species varies. Specifically, a coleopteran insect, Tenebrio molitor, is less susceptible to S. feltiae than are lepidopteran insects. We analyzed the low virulence of S. feltiae against T. molitor sequentially, in entering the gut lumen and penetrating the hemocoel, and in hemocoelic immune defenses by comparing the responses to those of a lepidopteran insect, Spodoptera exigua. Infective juveniles (IJs) of S. feltiae exhibited higher virulence and produced more progeny IJs in S. exigua than in T. molitor. The difference in IJ behavior was observed in the IJ invasion rate (IJs in gut lumen/IJs treated) after treatment, in which a lower rate was observed in T. molitor (20.4%) than in S. exigua (55.5%). Also, a lower hemocoelic penetration rate of IJs (IJs in hemocoel/IJs in gut) was observed in T. molitor (54%) than in S. exigua (74%) 24 h after feeding treatment. To investigate the immune defense in the hemocoel, insect hemolymph samples were incubated with IJs. The encapsulation behavior and phenoloxidase activity was higher in T. molitor hemolymph than in S. exigua hemolymph, which resulted in a significantly higher nematicidal activity in S. exigua. The humoral immune responses against S. feltiae were also different between the two species. The expression of two antimicrobial peptides, cecropin and attacin 1, was much higher in T. molitor. Furthermore, eicosanoid biosynthetic activity against S. feltiae was different in the two host species; sPLA activity was highly inducible in T. molitor but not in S. exigua. These results suggest that variability of the immune defense in the target insects, as well as in the invasion and penetration rates of IJs to the hemocoel, plays a crucial role in determining the insecticidal virulence of S. feltiae.
一种昆虫病原线虫，斯氏线虫 S. feltiae K1，对各种昆虫宿主具有致病性，但其对目标昆虫物种的毒力不同。具体来说，鞘翅目昆虫黄粉虫比鳞翅目昆虫对 S. feltiae 的敏感性更低。我们通过比较鞘翅目昆虫黄粉虫和鳞翅目昆虫甜菜夜蛾对 S. feltiae 的反应，依次分析了 S. feltiae 对黄粉虫低毒力的原因，包括进入肠道腔和穿透血腔，以及血腔免疫防御。斯氏线虫的感染性幼虫（IJs）在鳞翅目昆虫甜菜夜蛾中的毒力更高，产生的后代 IJs 也更多。在 IJ 入侵率（处理后的肠道腔中的 IJ/IJ 处理）方面观察到 IJ 行为的差异，其中黄粉虫中的 IJ 入侵率较低（20.4%），而在甜菜夜蛾中的 IJ 入侵率较高（55.5%）。此外，在喂食处理后 24 小时，黄粉虫中 IJ 的血腔穿透率（肠道腔中的 IJ/肠道腔中的 IJ）也较低（54%），而在甜菜夜蛾中 IJ 的血腔穿透率较高（74%）。为了研究血腔中的免疫防御，我们将昆虫血淋巴与 IJ 一起孵育。黄粉虫血淋巴中的包被行为和酚氧化酶活性高于甜菜夜蛾血淋巴，这导致在甜菜夜蛾中 IJ 的杀线虫活性显著提高。两种昆虫对 S. feltiae 的体液免疫反应也不同。两种抗菌肽（cecropin 和 attacin 1）在黄粉虫中的表达水平明显高于甜菜夜蛾。此外，两种宿主物种中针对 S. feltiae 的二十烷酸生物合成活性也不同；sPLA 活性在黄粉虫中高度诱导，但在甜菜夜蛾中不诱导。这些结果表明，目标昆虫的免疫防御的可变性，以及 IJ 对血腔的入侵和穿透率，在决定 S. feltiae 的杀虫毒力方面起着至关重要的作用。
