Department of Biology, University of Massachusetts, Amherst, Massachusetts, 01003, USA.
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853, USA.
Ecology. 2018 Nov;99(11):2535-2545. doi: 10.1002/ecy.2503. Epub 2018 Oct 12.
Hotspots of disease transmission can strongly influence pathogen spread. Bee pathogens may be transmitted via shared floral use, but the role of plant species and floral trait variation in shaping transmission dynamics is almost entirely unexplored. Given the importance of pathogens for the decline of several bee species, understanding whether and how plant species and floral traits affect transmission could give us important tools for predicting which plant species may be hotspots for disease spread. We assessed variation in transmission via susceptibility (probability of infection) and mean intensity (cell count of infected bees) of the trypanosomatid gut pathogen Crithidia bombi to uninfected Bombus impatiens workers foraging on 14 plant species, and assessed the role of floral traits, bee size and foraging behavior on transmission. We also conducted a manipulative experiment to determine how the number of open flowers affected transmission on three plant species, Penstemon digitalis, Monarda didyma, and Lythrum salicaria. Plant species differed fourfold in the overall mean abundance of Crithidia in foraging bumble bees (mean including infected and uninfected bees). Across plant species, bee susceptibility and mean intensity increased with the number of reproductive structures per inflorescence (buds, flowers and fruits); smaller bees and those that foraged longer were also more susceptible. Trait-based models were as good or better than species-based models at predicting susceptibility and mean intensity based on AIC values. Surprisingly, floral size and morphology did not significantly predict transmission across species. In the manipulative experiment, more open flowers increased mean pathogen abundance fourfold in Monarda, but had no effect in the other two plant species. Our results suggest that variation among plant species, through their influence on pathogen transmission, may shape bee disease dynamics. Given widespread investment in pollinator-friendly plantings to support pollinators, understanding how plant species affect disease transmission is important for recommending plant species that optimize pollinator health.
疾病传播热点会强烈影响病原体的传播。蜜蜂病原体可能通过共同利用花朵传播，但植物物种和花部特征变化在塑造传播动态方面的作用几乎完全未知。鉴于病原体对几种蜜蜂物种减少的重要性，了解植物物种和花部特征是否以及如何影响传播，可能为我们提供预测哪些植物物种可能成为疾病传播热点的重要工具。我们评估了 14 种植物物种上取食的非感染性熊蜂（Bombus impatiens）工蜂对原生动物肠道病原体克里米亚球虫（Crithidia bombi）的易感性（感染概率）和平均强度（感染蜜蜂的细胞计数）的变化，并评估了花部特征、蜜蜂体型和取食行为对传播的影响。我们还进行了一项实验，以确定在三种植物物种上（Penstemon digitalis、Monarda didyma 和 Lythrum salicaria），开放花朵的数量如何影响传播。植物物种之间取食熊蜂中克里米亚球虫的总体平均丰度差异了四倍（包括感染和未感染的蜜蜂）。在所有植物物种中，蜜蜂的易感性和平均强度随着每个花序的生殖结构数量（芽、花和果实）的增加而增加；体型较小和取食时间较长的蜜蜂也更容易感染。基于 AIC 值，基于性状的模型在预测易感性和平均强度方面与基于物种的模型一样好或更好。令人惊讶的是，花部大小和形态在物种间的传播中没有显著预测作用。在实验中，在 Monarda 中，更多的开放花朵使病原体丰度增加了四倍，但在其他两种植物中没有影响。我们的结果表明，植物物种之间的差异通过影响病原体的传播，可能会影响蜜蜂疾病动态。鉴于广泛投资于对传粉者友好的植物种植以支持传粉者，了解植物物种如何影响疾病传播对于推荐优化传粉者健康的植物物种非常重要。
