to the hypopharyngeal (brood food) glands of infected nurse bees (presumably as result of poor protein uptake in the gut) accelerates behavioural development in the bees leading to premature ageing (I know how they feel!) which can shorten a bee’s lifespan by 50% or more. The ventriculus (or mid-gut), which is normally brown, can become white and very fragile.
Winter bees have less protein in their fat bodies and haemolymph so will be less able to feed the new larvae in the spring should they live long enough to survive the winter.
Young queens can also get nosema and those that do are normally superseded very quickly, maybe within a month. However, queens are much less likely to get nosema because they don’t clean combs so can only be infected from ingesting contaminated food. Infected queens lay fewer eggs and new queen cells are less likely to hatch (sometimes being infected with black queen cell virus) leaving the colony open to queenlessness. Similarly, drones can become infected although they rarely are.
Nosema apis does not affect larvae, and young bees on hatching are always free of infection, only becoming infected if they come into contact with contaminated comb or food as part of their hive duties. However, with N ceranae, feeding larvae with contaminated pollen brought back by infected foragers prevents the removal of infection during the summer.
Differences between N apis and N ceranae
There is a strong seasonal relationship between the annual development of the colony and the number of Nosema apis spores. Once the weather improves the bees are able to defaecate outside the hive, removing infective spores. In addition, infected bees die away from the hive without transmitting their infection so spore levels reduce naturally in the summer.
This is not the case with Nosema ceranae which can cause problems for beekeepers all year round. Although the build-up of spore numbers is slower in N ceranae, their continual increase throughout the year means much higher infection levels can be reached even in the summer months. This leads to a constant loss of infected foraging bees and reduces the food brought into the hive. This is probably the main practical difference between the two types of nosema. If the bees are not thriving it is worth checking them for nosema.
Effects on the Colony
The effect of nosema on a colony really depends on the species of Nosema present, the time of year and the number of infected bees. Since the life span of the winter bees is shortened, colonies are more likely to die over the winter. Those that make it through may build up very slowly in the spring, or even dwindle and die out depending on the severity of the infection. To prevent nosema being a problem in the spring, check for it in the autumn.
Nosema levels will rise under any circumstances that remove opportunities for cleansing flights or force bees close together for long periods. Anything that confines the bees to the hive will exacerbate any nosema present (especially if they are stressed by other problems like dysentery). Travelling long distances with bees, bees sold as ‘packages’ and some management activities, such as queen rearing, will all serve to exacerbate nosema.
Over the winter nosema levels rise relentlessly. Consequently, a light infection of nosema in the autumn will become a heavy one by the spring. There is also a positive correlation of nosema with poor summer weather, which is likely to be especially significant for N ceranae. Bees are happiest in reliably hot summers; infected bees spend less time in contact with each other or cleaning the hive and bees dying away from the hive removes infection.
Although nosema and dysentery are often associated, bees can have dysentery without having nosema and vice-versa.
Dysentery is a separate condition caused by an excessive amount of water in a bee’s body, normally as a result of consuming food with a high water content which puts pressure on the ability of the bee’s gut to retain faeces. It is exacerbated by prolonged confinement during winter and early spring when there are fewer opportunities for the bees to defecate outside the hive.
Bees with nosema are more prone to dysentery because the changed water balance in the gut means their rectal contents build up more rapidly than normal. Sometimes faeces can be seen splattered about the frames and brood comb and around the hive entrance especially if Nosema ceranae is present.
Amoeba can also occur with Nosema. Amoeba is a protozoan (called Malpighamoeba mellifica) that lives in the Malpighian tubules (the bee’s equivalent to our kidneys). It can occur in