Issues facing the honey bee
Scientists are still unsure why so many bees are dying. Various different causes have been proposed: parasites, loss of suitable habitat, bad weather, pesticides. It is probably a combination of some or all of these factors:
Bees can suffer from several parasites including varroa and acarine mites, nosema fungus and ‘amoeba’.
Varroa mites are external parasites which can only reproduce in honey bee colonies. They can attack the larvae, pupae and adults. They weaken the bees by sucking their hemolymph (the fluid in their circulatory system) and spreading viruses such as deformed wing virus (DWV). A severe infestation of DWV can result in the death of the colony. This could be a contributing factor in Colony Collapse Disorder (CCD). It is one of the most significant causes of bee death in the UK and so all beekeepers must treat their hives for varroa. Treatment involves various different chemical sprays, which can only be used when there is no honey in the hive, and Integrated Pest Management (IPM) which removes mites at the most effective point in their breeding cycle. The queen is trapped and drone comb is removed thus restricting the cells available where the mites can breed.
Acarine (or tracheal) mites are rare in the UK. They infest the bees’ breathing tubes (tracheae), particularly the large tracheae at the front of the thorax. They shorten the life of the bees and therefore slow colony development, especially in the spring. As there are no external signs of infestation, diagnosis is done by dissecting a sample of bees and examining the tracheae. These should be a creamy white colour, but in infected bees they turn brown. There is no licensed chemical treatment for these mites but it seems that bees can develop resistance. The best course if action is probably to leave the colony to see if it recovers or to replace the queen with one from a more resistant strain of bee.
Nosema fungus has 2 different forms: Nosema apis and Nosema ceranae. The latter is widespread in the UK and seems to be the more virulent form of the disease. Bees infected with this fungus are less able to digest food, particularly pollen. Spores travel through their gut and are passed out in the faeces. Bees usually defecate outside of the hive but if they are prevented from going out by, for example, bad weather, they defecate inside. This is then cleaned by other bees who ingest the fungal spores and so the cycle continues. Nosema infection shortens the life of the bees and prevents the colony from developing as it should in the spring. If a colony is infected the frames should be removed, the comb burned and the frames sterilised before being used again. The hive also needs to be sterilised.
‘Amoeba’ is a protozoan, Malpighamoeba mellificae, which lives in the bee’s ‘kidneys’ (malpighian tubules). This is a rare disease and does not appear to affect the colony therefore it can be transferred onto clean comb if necessary. ‘Amoeba’ is spread in the same way as Nosema.
Sadly these are not the only issues threatening the honey bee. In Part 4 I’ll be talking about some of the others.
(This is an extract from my article which you can read in full here)