不同光照强度下兴安落叶松对舞毒蛾幼虫生长发育及防御酶的影响

为了探讨舞毒蛾对光照环境变化引起的落叶松抗性的变化是如何响应的，分析了不同光照强度处理的兴安落叶松对舞毒蛾幼虫生长发育状况和生理指标变化的影响。研究发现，取食50%和25%光照强度下生长的落叶松后，舞毒蛾幼虫平均体重、蛹重、化蛹率和羽化率与对照组相比均显著下降（P<0.05）。幼虫体内保护酶SOD、POD、CAT和解毒酶ACP、AKP、CarE、GSTs、MFO活性与对照组(100% 光照)相比均显著降低（P<0.05）且除CAT外在50%光照强度下降低最为显著（P<0.05）；4龄和5龄幼虫取食同一光强处理的落叶松后，SOD、POD、CarE、GSTs和MFO活性5龄显著低于4龄（P<0.05），ACP和AKP活性5龄却显著高于4龄（P<0.05）,表明昆虫在不同的发育阶段启用不同的排毒酶系。光照差异对取食人工饲料的舞毒蛾生长发育和排毒代谢酶活性均没有显著影响,说明舞毒蛾生长发育和酶活性的变化是因寄主植物抗性的影响而非光照强度的作用。本研究结果表明，采取适当的营林措施调节林分内的光照条件，可以提高落叶松的自主抗虫性，增强其抵御害虫危害的能力，有效控制害虫危害，减少化学农药的施用量。

Effects of the Larix gmelinii grown under different light intensities on the development and defensive enzyme activities of Lymantria dispar larvae

Larix gmelinii is among the most ecologically and economically important timber species in northeastern China due to its cold hardiness, drought resistance and rapid growth. Lymantria dispar L. is a defoliating insect pest which seriously harms larch during outbreaks. Plants, including trees, employ an array of physical and chemical constitutive defense mechanisms that play an important role in protection from insect herbivory. Constitutive defenses are always present, and because they are maintained even in undamaged plants, they are affected by environmental factors to some degree. In many organisms light is a crucial environmental signal influencing natural physiological and developmental processes. Different light intensities could induce changes in plant defense systems. However, pest insects can detoxify ingested plant secondary metabolites with their biotransformation system. We studied the developmental and physiological responses of Lymantria dispar larvae to changes in the constitutive defenses of Larix gmelinii under three sunlight intensities (100%, 50% and 25% of natural sunlight intensity ) mimicking the light conditions of forest edges, forest gaps and understories. The results showed that the detoxification enzyme activities of both fourth and fifth instar L. dispar larvae were significantly affected by their host L. gmelinii trees grown under the three different sunlight intensities. Compared with the control (100% sunlight intensity), the larval development (reflected by mean larval weight, pupation rate, mean pupal weight, adult emergence rate) of L. dispar was significantly inhibited after being fed on the needles of L. gmelinii grown under shaded conditions (P<0.05). The activities of the protective enzymes SOD, POD, CAT and detoxification enzymes ACP, AKP, CarE, GSTs, MFO in L. dispar larvae after fed on the needles of L. gmelinii grown under the shaded conditions (25% and 50% sunlight intensity) were significantly lower (P<0.05) than those in the larvae fed on the needles of L. gmelinii grown under the control (100% sunlight intensity) light condition. The activities of all the tested protective and detoxification enzymes excepting CAT were the most significantly inhibited after the larvae being fed on the needles of L.gmelinii grown under 50% sunlight intensity (P<0.05). These larval enzyme activities were significantly different (P<0.05) between fourth and fifth instar larvae while fed on the needles grown under the same light condition. The SOD, POD, CarE, GSTs and MFO activities in the fourth instar larvae were significantly higher than those of fifth instar larvae (P<0.05), while the ACP and AKP activities in the fifth instar larvae were significantly higher than those of fourth instar larvae (P<0.05). This result indicated that L. dispar might use different enzymes or enzyme complex for defense and/or detoxification during their larval development stages. However, light intensities did not show any significant direct effects on the growth development and defensive enzyme activities of L. dispar larvae on the artificial diets, indicating that the changes observed in L. dispar larval development and defensive enzyme activities were mainly caused by the larch resistance but not by the light intensity. Our results suggested that adjusting the light conditions rationally via silviculture approaches in the larch forests might not only increase the tree growth, but also increase the overall tree resistance to certain serious pest insects including L. dispar.