Michaud Kristen M, Irwin Rebecca E, Barber Nicholas A, Adler Lynn S
Department of Biology, University of Massachusetts, Amherst, MA.
Department of Applied Ecology, North Carolina State University, Raleigh, NC.
Environ Entomol. 2019 Jun 7;48(3):685-690. doi: 10.1093/ee/nvz018.
Bumble bee pollinators can be exposed to pathogens when foraging on flowers previously visited by infected individuals. Infectious cells may be deposited in floral nectar, providing a site for pathogens to interact with nectar secondary compounds prior to infecting bees. Some nectar secondary compounds can reduce pathogen counts in infected bumble bees, but we know less about how exposure to these compounds directly affects pathogens prior to being ingested by their host. We exposed the trypanosomatid gut pathogen, Crithidia bombi (Lipa & Triggiani 1988) (Trypanosomatida: Trypanosomatidae), to six different compounds found in nectar (aucubin, catalpol, nicotine, thymol, anabasine, and citric acid) for 1-h prior to ingestion by Bombus impatiens (Cresson 1863) (Hymenoptera: Apidae) workers that were then reared for 1 wk on a control diet. All of these compounds except citric acid reduce pathogen levels when consumed in hosts after infection, and citric acid is a common preservative found in citrus fruits and some honeys. We found that both citric acid and aucubin reduced Crithidia cell counts compared with controls. However, catalpol, nicotine, thymol, and anabasine did not have significant effects on Crithidia levels. These results suggest that Crithidia exposure in some floral nectars may reduce cell viability, resulting in a lower risk to visiting pollinators, but this effect may not be widespread across all flowering species.
大黄蜂传粉者在采食被感染个体先前访问过的花朵时可能会接触到病原体。感染性细胞可能会沉积在花蜜中，为病原体在感染蜜蜂之前与花蜜次生化合物相互作用提供了一个场所。一些花蜜次生化合物可以减少被感染大黄蜂体内的病原体数量，但我们对这些化合物在被宿主摄入之前如何直接影响病原体了解较少。我们让肠道锥虫病原体——熊蜂短膜虫（Crithidia bombi）（Lipa & Triggiani，1988年）（动基体目：锥虫科）在被凤蝶大黄蜂（Bombus impatiens）（Cresson，1863年）（膜翅目：蜜蜂科）工蜂摄入前1小时接触花蜜中发现的六种不同化合物（桃叶珊瑚苷、梓醇、尼古丁、百里酚、新烟草碱和柠檬酸），然后将这些工蜂在对照饮食上饲养1周。除柠檬酸外，所有这些化合物在感染后被宿主摄入时都会降低病原体水平，柠檬酸是柑橘类水果和一些蜂蜜中常见的防腐剂。我们发现，与对照相比，柠檬酸和桃叶珊瑚苷都降低了熊蜂短膜虫的细胞数量。然而，梓醇、尼古丁、百里酚和新烟草碱对熊蜂短膜虫水平没有显著影响。这些结果表明，在某些花蜜中接触熊蜂短膜虫可能会降低细胞活力，从而降低来访传粉者的风险，但这种影响可能并非在所有开花物种中都普遍存在。
