Community Research and Development Information Service - CORDIS

Microsporidia control and detection in bumble bee rearing

The Pollinator Prasites project has identified the current state of knowledge based on methods and data from the project combined with previous experiences and available published data, for developing the best strategy for Microsporidia detection and control in bumble bee breeding.

The simplest method for detection of N. bombi is search for spores in the Malpighian tubes and the ventriculus of bumble bees, using a squash preparation of the organs in tap water. A magnitude of 400 times is sufficient to detect the spores if present to some quantity. Dissection of the Malpighian tubes and ventriculus facilitates the checks. Detailed description of the detection and staining techniques of N. bombi see chapter II of the Pollinator Parasites Technical Report.

Molecular methods - PCR :
Comparative studies of light microscopy detection and the molecular techniques have demonstrated that PCR is a more sensitive way of detecting infection. An advantage using the molecular detection tool is that both spores and vegetative stages of the parasite will be detected, whereas light microscopy in squash preparations will detect spores only, unless preparations are also stained. The advantage of light microscopy is othat it is simple and rapid, and depending on the objective, may be sufficiently sensitive ( see chapter IV of the Pollinator parasites Technical report).

Control strategies

Quarantine of queens from nature:
A queen caught in the wild should not be introduced directly into the rearing facility without quarantine. When queens caught in the wild are used for pollination purposes, they should be separate from the rearing unit until at least 20 to 30 worker bees have emerged. This offspring must be checked for N. bombi by light microscopy (spores), or by molecular techniques for infection. When the queens and males are used to increase the gene pool, it is best to hibernate the new queens and then to introduce the next generation of queens in the actual rearing unit for production of new colonies.
Males become infected as well as queens and workers. Therefore the castes as well as the rearing box should be considered potential carriers of a nosema infection. Contact with nosema-diseased bees and faeces in the mating boxes, is a source of infection that should be avoided. Mating of non-infected queens with infected drones or even if they do not mate but are combined in a mating box, may transmit infection. Nosema infected colonies must be removed from the rearing facility as the infection will persist and will be passed on by infected queens.

Drifting of bumble bees is observed in greenhouses. Introduction of nosema spores via drifted workers or males is a serious risk if colonies are brought back from pollination assignments and reintroduced into rearing units. Reintroducing queens and males from old colonies into the rearing facility should always be avoided. In case it is necessary to return colonies, virgin queens or males used from pollination units should be placed in quarantine and be treated as colonies from the wild.

Nosema infections can be introduced via the food and food devices. Consequently, hygiene is important. All bumble bees in rearing facilities are fed with pollen, collected by honeybees and this material may be contaminated by Nosema apis. Spores of N. apis and spores of N. bombi are difficult to discriminate. In the wild, drones leave the colony and feed on and rest in flowers. In this way flowers and pollen may be contaminated with N. bombi spores. As pollen to be used in bumble bee rearing are collected by honey bees, N. bombi spores may possibly be introduced into rearing facilities. Therefore it is advisable to check the pollen to be fed to colonies in rearing units for nosema spores and avoid feeding Microsporidia spore contaminated pollen unless sensitive molecular detection techniques can exclude the presence of N. bombi (see chapter IV of the Technical Report).

It has been demonstrated that a low-level nosema infection may not be detected by light microscopy. Thus, even if no infection has been demonstrated using microscopy, general hygienic measures must be applied.

This means:
- No food, neither pollen nor sugar is transferred from one colony to another,
- No food devices are transferred from one box to another,
- Tweezers, food devices, mating chambers etc are cleaned using hot water and a disinfectant,
- Food is stored in refrigerators,
- Escaped bumble bees are captured and killed,
- Spoiled food is cleaned up,
- The complete facility is kept neatly,
- Materials that are a risk for spreading diseases and parasites like old colonies, colonies that are not developing normally, used boxes and dead bumble bees are handled and carried away in a way that free flying bumble bees can not reach it.

Reported by

Bornsesteg 47 PB 167
6708 PD Wageningen
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