Mason Charles J, Couture John J, Raffa Kenneth F
Department of Entomology, University of Wisconsin, 345 Russell Laboratories, 1630 Linden Dr, Madison, WI, 53706, USA,
Oecologia. 2014 Jul;175(3):901-10. doi: 10.1007/s00442-014-2950-6. Epub 2014 May 6.
Phytophagous insects must contend with numerous secondary defense compounds that can adversely affect their growth and development. The gypsy moth (Lymantria dispar) is a polyphagous herbivore that encounters an extensive range of hosts and chemicals. We used this folivore and a primary component of aspen chemical defenses, namely, phenolic glycosides, to investigate if bacteria detoxify phytochemicals and benefit larvae. We conducted insect bioassays using bacteria enriched from environmental samples, analyses of the microbial community in the midguts of bioassay larvae, and in vitro phenolic glycoside metabolism assays. Inoculation with bacteria enhanced larval growth in the presence, but not absence, of phenolic glycosides in the artificial diet. This effect of bacteria on growth was observed only in larvae administered bacteria from aspen foliage. The resulting midgut community composition varied among the bacterial treatments. When phenolic glycosides were included in diet, the composition of midguts in larvae fed aspen bacteria was significantly altered. Phenolic glycosides increased population responses by bacteria that we found able to metabolize these compounds in liquid growth cultures. Several aspects of these results suggest that vectoring or pairwise symbiosis models are inadequate for understanding microbial mediation of plant-herbivore interactions in some systems. First, bacteria that most benefitted larvae were initially foliar residents, suggesting that toxin-degrading abilities of phyllosphere inhabitants indirectly benefit herbivores upon ingestion. Second, assays with single bacteria did not confer the benefits to larvae obtained with consortia, suggesting multi- and inter-microbial interactions are also involved. Our results show that bacteria mediate insect interactions with plant defenses but that these interactions are community specific and highly complex.
植食性昆虫必须应对众多会对其生长发育产生不利影响的次生防御化合物。舞毒蛾（Lymantria dispar）是一种多食性食草动物，会接触到种类繁多的宿主和化学物质。我们利用这种食叶动物以及白杨化学防御的一种主要成分——酚糖苷，来研究细菌是否能解毒植物化学物质并使幼虫受益。我们进行了昆虫生物测定，使用从环境样本中富集的细菌，分析生物测定幼虫中肠的微生物群落，并进行体外酚糖苷代谢测定。在人工饲料中存在酚糖苷但不存在酚糖苷的情况下，接种细菌都能促进幼虫生长。细菌对生长的这种影响仅在喂食来自白杨树叶细菌的幼虫中观察到。不同细菌处理后，中肠群落组成各不相同。当饲料中含有酚糖苷时，喂食白杨细菌的幼虫中肠组成会发生显著变化。酚糖苷增加了我们发现能够在液体生长培养物中代谢这些化合物的细菌的群体反应。这些结果的几个方面表明，在某些系统中，载体或成对共生模型不足以理解微生物对植物 - 食草动物相互作用的介导作用。首先，最有利于幼虫的细菌最初是叶面栖息者，这表明叶际居民的毒素降解能力在被摄入后会间接使食草动物受益。其次，单一细菌的测定并未给幼虫带来与细菌群落相同的益处，这表明多微生物和微生物间的相互作用也参与其中。我们的结果表明，细菌介导昆虫与植物防御的相互作用，但这些相互作用具有群落特异性且高度复杂。
