紫外辐射对9个昆虫病原线虫品系存活率和致病力的影响

为探明紫外辐射对昆虫病原线虫（entomopathogenic nematodes，EPN）的作用，以甘肃省分离得到的昆虫病原线虫为研究材料，用室内模拟生测法，测定了经20 W、40 W紫外线辐射后，斯氏属（Steinernema feltiae，S.kraussei）和异小杆属（Heterorhabditis brevicaudis，H.megidis）4种昆虫病原线虫9个品系的存活率，并以大蜡螟（Galleria mellonella）为供试昆虫，采用改良的ONE ON ONE法，测定了其对大蜡螟的致病力。结果表明：经UV-B辐射后供试的9个昆虫病原线虫品系存活率未发生显著变化（P>0.05）。20 W紫外辐射30 min后，S.feltiae 0639C和0663TD 2品系对大蜡螟的致病力提高，其中S.felitiae 0639C致病力显著升高（P<0.05），侵染32 h后，寄主昆虫死亡率由13.3%升高到73.3%；S.felitiae 0661YM品系的致病力显著降低（P<0.05），侵染32 h后，寄主昆虫死亡率率由66.7%降低到0；其余各品系致病力均无显著变化。不同辐射时长和辐射强度对S.felitiae 0639C和0663TD引起寄主昆虫死亡的时间有影响，较对照组而言，经辐射预处理后，2品系线虫引起寄主昆虫死亡的时间均提前，其中S.felitiae 0639C随着辐射强度的增大引起寄主昆虫开始死亡时间提前，而S.felitiae 0663TD随着辐射强度增加引起寄主昆虫开始死亡时间延后。不同紫外辐射时长对S.felitiae 0663TD和S.felitiae 0639C致病力无显著影响，30 min、60 min、90 min、120 min辐射处理之间差异不显著（P>0.05）。研究表明，9个供试昆虫病原线虫品系均对UV-B辐射具有一定的耐受能力；20 W UV-B辐射30 min，能刺激S.felitiae 0663TD和S.felitiae 0639C侵染和致死寄主昆虫；一定的辐射时长内（120 min），辐射时长对S.felitiae 0663TD和S.felitiae 0639C的致病力无影响。

Effects of UV-B radiation on entomopathogenic nematode survival and pathogenicity

Entomopathogenic nematodes (EPN) possess many positive attributes as biocontrol agents. They are safe to humans and generally safe to other non-target organisms. To investigate the effects of ultraviolet radiation exposure on EPN, we studied the effects of 20 or 40 W UV-B radiation for different time lengths (30, 60, 90, or 120 min) on the virulence of EPN infective juveniles (IJs) to Galleria mellonella, including 9 strains from 4 species (Steinernema feltiae, S. kraussei, Heterorhabditis brevicaudis, and H. megidis) isolated from Gansu Province. The results showed that there were no differences among the strains in the survival rate of IJs with and without 30 min UV-B irradiation. The virulence of IJs varied among strains after exposure to 20 W ultraviolet radiation for 30 min: virulence of two strains (S. felitiae 0639C and S. feltiae 0663TD) was increased (P<0.05), that of one strain (S. feltiae 0661YM) decreased (P<0.05), and that of all others (H. brevicaudis 0641TY, H. megidis 0627M, S. felitiae 0639C, S. felitiae 0619HT, S. kraussei 0663HT, and S. kraussei 0657L) showed no significantly change (P> 0.05). For example, when measured at 32 h after infection, the mortality rate of host insects infected by S. felitiae 0639C increased significantly, from 13.3% to 73.3% (P<0.05), whereas that of insects infected by S. felitiae 0661YM decreased significantly from 66.7% to zero (P<0.05). At the same time, treating S. felitiae 0639C and 0663TD with UV affected host mortality 24 h after exposure to IJs:for S. felitiae 0639C, host mortality at 24 h was greater in the 40 W treatment than in either control or the 20 W treatment; for S. felitiae 0663TD, host mortality at 24 h was greater in the 20 W treatment than in either the control or the 40 W treatment. Ultraviolet radiation duration (30 min, 60 min, 90 min, or 120 min exposure) had no effect on the pathogenicity of S. felitiae 0663TD or S. felitiae 0639C (P> 0.05). Therefore, the following conclusions were drawn:All of the 9 tested strains of EPN isolated from Gansu Province had some tolerance to UV-B radiation, and, in particular, S. felitiae 0622L had a high tolerance to ultraviolet radiation. In addition, ultraviolet radiation had a variable impact on the pathogenicity of EPN in Gansu Province, as there were differences among different species and strains. For example, 20 W UV-B radiation for 30 min enhanced the pathogenicity of S. felitiae 0663TD, whereas it significantly weakened that of S. felitiae 0661YM. Ultraviolet radiation stimulated S. felitiae 0663TD and S. felitiae 0639C to infect and kill host insects more quickly, although the radiation intensity that optimized the 24-h mortality rate varied between the two strains. After 48 h, however, there was no significant difference in the pathogenicity of S. felitiae 0663TD and S. felitiae 0639C between the different radiation intensities (20 and 40 W). Additionally, IJs of S. felitiae 0663TD and S. felitiae 0639C both had high pathogenicity after 48-72 h, regardless of the radiation intensity (20 W or 40 W) or the duration of exposure (30, 60, 90, or 120 min). These findings will shed more light on using entomopathogenic nematodes under ultraviolet radiation stress.