Dysentery in Honeybees

Introduction

Nosema apis is a parasitic Microsporan organism that can cause Nosema disease and dysentery in honeybees. The group Microspora are unicellular and spore-forming in nature. They are not visible with the naked eye; microscopic examination is necessary.
Infection

All adult bee castes can be infected by Nosema disease with serious consequences for the colony. Nosema apis spores are ingested and then germinate very quickly ( Bailey, 1955 ) invading the mid-gut and epithelial cells of the bee. Huge numbers of spores, often more than 30 million, can be found in the mid-gut during a Nosema infection (Bailey and Ball, 1991).
Colony Effects

Although infected bees do not outwardly appear any different from non-infected individuals, Nosema-infected colonies can be recognised by certain traits even before microscopic analysis and confirmation of disease:

The lifespan of infected bees can be greatly reduced and such colonies dwindle in late winter or early spring.

Nosema infection promotes over-accumulation of water in the body of adult bees leading to dysentery. Digestion and production of royal jelly in worker bees can be severely affected. Because of restriction to the hive in winter temperatures, dysenteric bees defecated within the hive, on the combs and hive walls. This is more obvious in spring when liquid faecal spots can be seen on the outside of the hive also from the first cleaning flights.
Although infected bees do not outwardly appear any different from non-infected individuals, Nosema-infected colonies can be recognised by certain traits even before microscopic analysis and confirmation of disease:


When worker bees clean the hive they become infected with spores from this faecal material. Cleaning behaviour and polishing increases rapidly during the spring season and consequently the level of Nosema infection rises sharply during this time.

Nosema infection alters the behaviour of young adult bees so that they cease brood rearing and attending the queen earlier than normal and begin foraging and hive guarding like older bees (Wang and Moeller, 1970). Honey yields can be reduced in Nosema-infected colonies due to such reduction in brood care and provision of new workers for foraging.

The life span and egg production in infected queens is much reduced and supersedure is then common.


Treatment

Good husbandry on the part of the beekeeper will help to prevent the incidence of Nosema within a colony. Damp apiary sites and lack of nutrients together with any other stress factors such as lack of space or infection with other disease can contribute to Nosema proliferation.

The fungal product fumagillin when fed to honeybee colonies suppresses the effects of Nosema apis and can be administered as a prophylactic or as a control treatment.