Mythimna separata (Lepidoptera: Noctuidae) is an omnivorous pest that poses a great threat to food security. Insect antimicrobial peptides (AMPs) are small peptides that are important effector molecules of innate immunity. Here, we investigated the role of the AMP cecropin B in the growth, development, and immunity of M. separata. The gene encoding M. separata cecropin B (MscecropinB) was cloned. The expression of MscecropinB was determined in different developmental stages and tissues of M. separata. It was highest in the prepupal stage, followed by the pupal stage. Among larval stages, the highest expression was observed in the fourth instar. Tissue expression analysis of fourth instar larvae showed that MscecropinB was highly expressed in the fat body and haemolymph. An increase in population density led to upregulation of MscecropinB expression. MscecropinB expression was also upregulated by the infection of third and fourth instar M. separata with Beauveria bassiana or Bacillus thuringiensis (Bt). RNA interference (RNAi) targeting MscecropinB inhibited the emergence rate and fecundity of M. separata, and resulted in an increased sensitivity to B. bassiana and Bt. The mortality of M. separata larvae was significantly higher in pathogen plus RNAi-treated M. separata than in controls treated with pathogens only. Our findings indicate that MscecropinB functions in the eclosion and fecundity of M. separata and plays an important role in resistance to infection by B. bassiana and Bt.

中文翻译：

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抗菌肽天蚕素 B 在粘虫病原菌抗性中发挥作用

粘虫（鳞翅目：夜蛾科）是一种杂食性害虫，对粮食安全构成极大威胁。昆虫抗菌肽（AMP）是小肽，是先天免疫的重要效应分子。在这里，我们研究了 AMP 天蚕素 B 在生长、发育和免疫中的作用分离分枝杆菌。基因编码分离分枝杆菌天蚕素 B (麦草素B）被克隆。的表达式为麦草素B是在不同的发育阶段和组织中确定的分离分枝杆菌。预蛹期最高，其次为蛹期。在幼虫阶段中，在第四龄观察到最高表达。四龄幼虫的组织表达分析表明麦草素B在脂肪体和血淋巴中高度表达。人口密度的增加导致了上调麦草素B表达。麦草素B第三龄和第四龄的感染也使表达上调分离分枝杆菌和白僵菌或者苏云金芽孢杆菌（转氨酶）。 RNA 干扰 (RNAi) 靶向麦草素B抑制了出苗率和繁殖力分离分枝杆菌，并导致对白僵菌和转氨酶。死亡率为分离分枝杆菌经 RNAi 处理的病原体中幼虫的数量显着增加分离分枝杆菌与仅用病原体处理的对照相比。我们的研究结果表明麦草素B在羽化和繁殖中发挥作用分离分枝杆菌并在抵抗感染方面发挥重要作用白僵菌和转氨酶。