Abstract：
This work examines the insecticidal activity of octanoic acid (C8:0), a short-chain fatty acid detected in entomopathogenic fungus - Conidiobolus coronatus medium, against Lucilia sericata larvae and adults. The LD50 value was calculated as 3.04±0.26 µg/mg (3040 mg/kg) of insect body mass, which places the compound in category 5 of acute toxicity (slightly hazardous). The presented research also describes its probable mechanism, with a particular focus on changes in two main insect defense mechanisms: (1) the composition of the cuticle (GC-MS analysis) and (2) immunocompetent cells (microscopic analysis of cultured hemocytes). More precisely, octanoic acid application resulted in changes in cuticular free fatty acid (FFA) profiles in both adults and larvae; generally, treatment increased short-chain FFAs, and a decrease of middle- and long-chain FFAs. Both in vivo and in vitro applications of octanoic acid resulted in vacuolisation, disintegration, and destruction of nets formed by plasmatocytes. As the compound has also previously been found to be toxic against Galleria mellonella, it appears to have lethal potential against insects in both the Orders Diptera and Lepidoptera, indicating it may have strong entomopathogenic potential. It is worth noting that octanoic acid is approved as a food additive with well-documented insecticidal activity, and hence may be a valuable component in the design of new insecticides that are safe for both humans and the environment.
摘要：
这项工作检查了辛酸（C8：0）的杀虫活性，在昆虫病原真菌-分生孢子培养基中检测到的短链脂肪酸，对抗丝裂藻幼虫和成虫。LD50值计算为3.04±0.26µg/mg（3040mg/kg）昆虫体重，将该化合物置于急性毒性的第5类(轻微危险)。本研究还描述了其可能的机制，特别关注两种主要昆虫防御机制的变化：（1）角质层的组成（GC-MS分析）和（2）免疫活性细胞（培养血细胞的显微镜分析）。更确切地说,辛酸的施用导致成虫和幼虫角质层游离脂肪酸（FFA）谱的变化；通常，治疗增加了短链FFA，以及中链和长链FFA的减少。辛酸的体内和体外应用均导致空泡化，解体,和破坏由浆细胞形成的网。由于该化合物以前也被发现对Galleriamellonella有毒，它似乎对双翅目和鳞翅目的昆虫都有致命的潜力，表明它可能有很强的昆虫致病潜力。值得注意的是，辛酸被批准为具有良好杀虫活性的食品添加剂，因此可能是对人类和环境都安全的新型杀虫剂设计中的有价值的组成部分。
