Pathogens play a key role in insect population dynamics, contributing to short-term fluctuations in abundance as well as long-term demographic trends. Two key factors that influence the effects of entomopathogens on herbivorous insect populations are modes of pathogen transmission and larval host plants. In this study, we examined tritrophic interactions between a sequestering specialist lepidopteran, Euphydryas phaeton, and a viral pathogen, Junonia coenia densovirus, on its native host plant, Chelone glabra, and a novel host plant, Plantago lanceolata, to explore whether host plant mediates viral transmission, survival, and viral loads. A two-factor factorial experiment was conducted in the laboratory with natal larval clusters randomly assigned to either the native or novel host plant and crossed with either uninoculated controls or viral inoculation (20% of individuals in the cluster inoculated). Diapausing clusters were overwintered in the laboratory and checked weekly for mortality. At the end of diapause, all surviving individuals were reared to adulthood to estimate survivorship. All individuals were screened to quantify viral loads, and estimate horizontal transmission postmortem. To test for vertical transmission, adults were mated, and the progeny were screened for viral presence. Within virus-treated groups, we found evidence for both horizontal and vertical transmission. Larval clusters reared on the native host plant had slightly higher horizontal transmission. Survival probability was lower in clusters feeding on the native host plant, with inoculated groups reared on the native host plant experiencing complete mortality. Viral loads did not differ by the host plant, although viral loads decreased with increased sequestration of secondary compounds on both host plants. Our results indicate that the use of a novel host plant may confer fitness benefits in terms of survival and reduced viral transmission when larvae feeding on it are infected with this pathogen, supporting hypotheses of potential evolutionary advantages of a host range expansion in the context of tritrophic interactions.

中文翻译：

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宿主植物介导的病毒传播及其对本地蝴蝶的影响

病原体在昆虫种群动态中发挥着关键作用，导致昆虫丰度的短期波动以及长期人口趋势。影响昆虫病原体对草食性昆虫种群影响的两个关键因素是病原体传播方式和幼虫寄主植物。在这项研究中，我们研究了一种隔离专家鳞翅目植物Euphyyas phaeton和一种病毒病原体 Junonia coenia densovirus 在其原生寄主植物Chelone glabra和一种新寄主植物车前草(Plantago lanceolata ) 上的三营养相互作用，以探讨寄主植物是否介导病毒传播、存活和病毒载量。在实验室中进行了双因素析因实验，将出生幼虫簇随机分配给本地或新宿主植物，并与未接种的对照或病毒接种（簇中 20% 的个体接种）杂交。滞育簇在实验室中越冬，并每周检查死亡率。在滞育结束时，所有幸存的个体都被抚养至成年以估计存活率。所有个体均经过筛查以量化病毒载量，并估计死后水平传播情况。为了测试垂直传播，将成虫交配，并筛选后代是否存在病毒。在病毒治疗组中，我们发现了水平和垂直传播的证据。在本地寄主植物上饲养的幼虫簇具有稍高的水平传播。以本地寄主植物为食的群体的存活概率较低，而在本地寄主植物上饲养的接种群体则完全死亡。尽管病毒载量随着两种宿主植物上次要化合物的封存增加而减少，但病毒载量并没有因宿主植物而异。我们的结果表明，当以新宿主植物为食的幼虫感染了这种病原体时，使用一种新的宿主植物可能会在生存方面带来适应性益处，并减少病毒传播，这支持了三营养背景下宿主范围扩大的潜在进化优势的假设。互动。