Bumblebee Sector Guide To The National Bee Farm-level Biosecurity Standard
Appendix C: Descriptions of Bumblebee Pests

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The following list is a brief overview of the main pests that are of concern to the commercial bumblebee-rearing sector, bumblebee distributors, and maintenance service providers, greenhouse operators, field crop producers, and the scientific research community.

Nosema

Nosema bombi is a unicellular microsporidian fungal parasite. Transmission occurs through the spores that are spread during feeding of brood and adults when the spores germinate and infect the mid gut cells and the malpighian tubes.

Nosema disease spores may be present in bee feces or dead bee residue on surfaces or water spills that have been contaminated by bee feces. Spores can be viable on these surfaces for extended periods of time. Bee treatments, such as Fumagilin-B, control the vegetative stage of Nosema within the bee but don not kill spores on surfaces.

The result is less brood or less viable workers. There is no known or obvious treatment.

Crithidia

Crithidia bombi is a unicellular organism that attaches exclusively to the gut walls and is subsequently excreted through the feces. Crithidia is spread either through commingling in the nest or via foraging on flowers previously contaminated by other bumblebees.

While death is uncommon from Crithidia, workers whose gut is infected with the protozoan are less likely to forage, because infected bees lose their ability to distinguish between flowers containing nectar and those that do not. The lifespan of an infected bumblebee can be shortened, and there is the potential to adversely affect the health of other bees in the hive. Crithidia inhibits colony founding, and reduces host longevity and colony fitness.

Crithidia is unlikely to survive for long periods of time, but it does survive in the gut of overwintering queens, which have been found to infect the progeny that is produced the following spring.

Tracheal Mites

Locustacarus buchneri is a parasitic tracheal mite that can be very destructive to certain species of bumblebees and can affect both wild and commercial bumblebee populations. Hatching larvae form over winter in the trachea of the hibernating bumblebee queens and lay their eggs shortly after she emerges in the spring. The parasite is then transferred in the nest to other bumblebees, but it is uncertain how well the tracheal mites would survive in other locations such as buildings and equipment.

The possibility exists that large numbers of the parasites can cause the host worker bumblebee to become lethargic and cease foraging. The resulting reduction of nectar to the colony can then diminish colony growth and reproduction. Likewise, there can be a reduction in the lifespan of the infected host bumblebee.

Tracheal mites are too small to be seen without the aid of a microscope. Microscopic tests may be performed by growers that have been properly trained in sampling, slide preparation, and identification procedures. As an alternative, they could be identified by a diagnostic bee laboratory.

Brood Parisitoids (Mellitobia)

Mellitobia acasta and Mellitobia chalybii are naturally occurring parasitic wasps that can adversely affect individual bumblebee hosts or the viability of an entire hive by attaching themselves to a host queen and reproducing in large numbers. This is a problem that must be monitored, especially in the greenhouse environment.

Small Hive Beetle

It has been demonstrated in quarantine facilities that small hive beetles can parasitize bumblebee hives. However, it is unclear how serious the damage could be from this potentially emerging pest for bumblebees, but in honey bee hives, the larvae of small hive beetle do the most damage in the colony, in some cases consuming the brood and food stores. The level of harm to the colony depends on the number of beetle larvae present. Once present in large numbers, the survival of the colony may be at great risk.

Wax Moth

A wax moth adult may enter a bumblebee hive to lay her eggs. Initially, the caterpillars (larvae) feed on debris, but as they grow they may switch to feed stores, but an invasion of the nest does not always lead to the destruction of the nest, as it does not feed on the larvae. The wax moth is also a serious pest for honey bees.

Honey Bee Pests

Honey bee colonies are strongly affected by several pathogens, including chalkbrood and the viruses causing colony collapse disorder. Some of these diseases may survive through long periods of latency or dormancy. While these diseases have not yet been shown to have any significant effects on bumblebee colonies, there is the potential for inter-species transmission among Hymenoptera. As this document should be considered a living document, it is essential that a grower stay informed about developing issues with other pests that affect bumblebees and other bee species.

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