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  • Writer's pictureJohn Mackay

Familiar Foes – But Which is Worse?


By John Mackay

When we test bees in the lab for a range of pathogens, we can obtain precise quantities on a range of bacteria, fungi-like cells and viruses – and often the colony appears healthy. Some new work published is a return to 10 years ago and triggers us with two words: ceranae and passim. As in Nosema ceranae and Lotmaria passim – two of the pathogens we found during a syndrome that first broke out in the Coromandel and the Wairarapa back in 2014.

Where’d they go? A sign of Nosema ceranae is a dwindling bee population.

Thus, it seems appropriate that it was Dr Oksana Borowik who sent this recent paper through to me – a commercial beekeeper and scientist who drove much of the research into what was leading to the deaths of hundreds (and thousands nationally) of spring nucs and colonies. Our laboratory was the first to confirm that bees from these colonies had very high levels of both Nosema ceranae (only recently discovered in NZ at that time) and Nosema apis (which has always been present in New Zealand’s honey bees, as far as we know). At the same time, a newly classed organism known as a trypanosome had been reported in the USA. It didn’t escape Oksana’s attention, but we had already designed a DNA test for this new Lotmaria passim and soon confirmed it was present in these spring dwindling hives (Stuff, 2015).

It always needs to be said, this was a new detection – not a new introduction into New Zealand. From our bee testing around the country, L. passim turned out to be widespread and at varying levels among bee samples. Without seeing the health of the colonies, it has been difficult to accurately assess the effects of L. passim as a hive measure. A story unto itself (previously believed to be another organism), L. passim has been associated with major overwintering losses in Belgium (Ravoet et al., 2013, note: this work’s title shows Crithida mellificae, but it was later shown to be all L. passim).

Dysentery in honey bees is a sign that hives might be suffering Nosema and it is more common in Nosema apis than ceranae.

The newest work turns this to a tale of two parasites – literally, it’s in the title of the open access paper A tale of two parasites: Responses of honey bees infected with Nosema ceranae and Lotmaria passim. The authors infected newly-emerged bees with either or both N. ceranae and L. passim and used two measures of bee health – the time taken for half the bees to die as well as their interest in higher sugar concentrations (acting as a marker for hunger or energy stress). It could be expected (as the authors did) that the double whammy of both L. passim and N. ceranae would shorten the lifespan, compared to one or other organism alone. And that the interest in sugar would also increase due to the energy stress from the pathogen(s).

Nope. Nosema ceranae alone turned out to be the most pathogenic – shortening the lives of the bees in this experiment, by four days compared to the mixed infection of N. ceranae and L. passsim. The mixed infection in turn led to bee deaths 8 days sooner than L. passim alone … which shortened lifespans by another 8 to 11 days. In short, N. ceranae was shortening lifespans of bees by nearly 3 weeks! The pathogens did lead to increased sugar feeding, but there was no statistical difference among the pathogens/mixture of pathogens.

Coromandel beekeeper and scientist Dr Oksana Borowick is well versed in Nosema ceranae, having identified it in her hives in 2014 and thus putting the apiculture industry on alert.

It can be difficult to compare this decrease with other studies where N. ceranae has been fed to bees. A previous study showed a double hit of its own kind when it compared N. ceranae to N. apis and mixtures of the two (Milbrath et al., 2014). Here the bees were fed 30,000 spores (median decrease of seven days) whereas this current work fed three times higher amounts. However the current work confirms the mortality effects by L. passim and once more shows the danger of (often invisible) nosemas in bees.

(Editor’s note: John excellently described how beekeepers could identify the signs of nosema in their hives in this September 2022 column.)

John Mackay is a molecular biologist and the technical director of Gisborne-based lab dnature diagnostics and logistics, as well as a hobby beekeeper.


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