Abstract
Nosema ceranae causes a widespread disease that reduces honey bee health but is only thought to infect adult honey bees, not larvae, a critical life stage. We reared honey bee (Apis mellifera) larvae in vitro and provide the first demonstration that N. ceranae can infect larvae and decrease subsequent adult longevity. We exposed three-day-old larvae to a single dose of 40,000 (40K), 10,000 (10K), zero (control), or 40K autoclaved (control) N. ceranae spores in larval food. Spores developed intracellularly in midgut cells at the pre-pupal stage (8 days after egg hatching) of 41% of bees exposed as larvae. We counted the number of N. ceranae spores in dissected bee midguts of pre-pupae and, in a separate group, upon adult death. Pre-pupae exposed to the 10K or 40K spore treatments as larvae had significantly elevated spore counts as compared to controls. Adults exposed as larvae had significantly elevated spore counts as compared to controls. Larval spore exposure decreased longevity: a 40K treatment decreased the age by which 75% of adult bees died by 28%. Unexpectedly, the low dose (10K) led to significantly greater infection (1.3 fold more spores and 1.5 fold more infected bees) than the high dose (40K) upon adult death. Differential immune activation may be involved if the higher dose triggered a stronger larval immune response that resulted in fewer adult spores but imposed a cost, reducing lifespan. The impact of N. ceranae on honey bee larval development and the larvae of naturally infected colonies therefore deserve further study.
Highlights
Honey bees provide valuable pollination services for multiple agricultural crops [1,2]
We focus on a globally-distributed pathogen, Nosema ceranae, which significantly reduces the survival of bee colonies [10,11]
Nosema ceranae infection contributes to poor honey bee health globally and is thought to only infect adult honey bees
Summary
Honey bees provide valuable pollination services for multiple agricultural crops [1,2]. Despite the increasing global demand for this pollination service [3], problems with bee health have contributed to limiting the supply of colonies [4]. Each year since 2006, the USA has experienced consecutive overwintering colony losses of approximately 30% [5], and some European countries have reported similar losses [6,7]. The causes for these declines are not PLOS ONE | DOI:10.1371/journal.pone.0126330. The causes for these declines are not PLOS ONE | DOI:10.1371/journal.pone.0126330 May 27, 2015
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