Varroa: The Heart of the Problem, Part 5.

The Week.

This first week of January brought winter snow to the hills and uplands and a hard frost everywhere. Yesterday the temperature didn’t rise above freezing and, combined with bright sunshine, gave crystal clear visibility to spectacular views in the distance. Sound seemed closer too and a train far away could be heard as if only a few hundred yards off. Sunshine reflecting from its doors showed up clearly the short commuter train heading to Inverness from Aberdeen though it was some three miles away as the crow flies.

Reviewing my 5 years- on- one- page nature diary, I note that this week is much colder than last year and that there are few flowers and shrubs blooming in comparison. Last year on the 5th I recorded sweet box, witch hazel, wallflower, and primula making floral appearances with butterbur pushing up in the apiary. These are not to be seen today.

I’ve walked 19 miles so far this year with two more days till the end of the first week. On a short local walk the other day, up ahead a small boy in a bright yellow quilted jacket is walking with his granny. He’s ferociously bashing hogweed, Heracleum sphondylium, with a stick. As I get closer I hear him telling granny that it’s poisonous. She’s telling him that he’s mistaken so I stop to back up granny explaining that giant hogweed, Heracleum mantegazzianum, certainly is but that this is a different plant, though from the same family. It is harmless and the seeds are very useful to birds at this time of year. I tell him that I’ve seen chaffinches feeding on them just the other day. To a small boy this plant must look enormous and very similar in many ways to giant hogweed so I compliment him on his knowledge of plants. We stand for a while beside the hogweed with its array of seedpods glittering in the frost talking about its value to honey bees and other pollinators for nectar and pollen sources in summer. The small boy is bright and engaging and his face lights up when I mentioned bees. He asks if I know Connie and if I am the “Bee Lady”. This brings a smile to my face and I make a mental note to invite him with his granny to visit my bees in the new season. It never ceases to amaze me; the curiosity of children and their knowledge of the environment. I think that there may be a greater focus on environmental awareness in schools at the moment and it bodes well for the future.

The colonies all have stores of fondant sitting directly over the brood nests. I had to shift one bag over a bit to cover the cluster but the others were all in place.

Varroa: population growth.

Back to the varroa story and population growth. How fast the varroa population grows depends upon several variables including season and colony strength. There will be an increase in varroa reproduction when there are drone brood cells for them to lay eggs in. Even if colonies have been treated for varroa by the beekeeper, there will be re infestations in situations of robbing by infested bees, and through infested bees drifting into other hives.

In the UK we have what is called a threshold level of varroa above which there is risk of poor colony outcome and collapse. We use 1,000 mites per colony as this threshold marker though other countries may use another level. Of course, there are many factors that make this just an estimate, such as varying colony sizes. If you use the sugar roll test and collect a sample of 300 bees this is a 200th of a 60,000 worker- strong colony. If you have 6 mites in the sample this indicates that you have around 1,800 varroa mites in the hive at this time.

Beekeeper Action.

The beekeeper can reduce the number of colonies in an apiary if it is overcrowded, and increase as much as possible the space between hives to reduce drifting. To reduce the robbing risk I keep the entrances small at all times unless there is a tremendous nectar flow with bees queuing up to get inside with their loads. I will temporarily increase entrance size during the flow.

If varroa levels are low at the start of the season then the better the outcome is likely to be. If you take 50 varroa mites/colony as the winter threshold level and you treat the colony at the end of summer, so they go into winter with low levels, you give them a better chance of making it through winter. Going into winter with more than 50 mites/colony reduces their survival chances because more bees will die early and there will be fewer to maintain the winter cluster and keep warm. Starting spring with fewer than the winter mite threshold of 50 means that it will take longer for varroa to build up to harmful levels as the season progresses and brood rearing increases.

With effective varroa control treatments mite levels may be kept low enough to prevent harm. Research shows that in temperate climates a colony will last around 3-4 years without treatment before it collapses and dies. There will be some colonies that do not die though and this premise forms the basis of the Bond strategy which is the “live and let die” management plan adopted by some beekeepers who decide to become treatment free and allow only the strong colonies to survive and propagate. This is not something that I will do because I only have 10 colonies currently, and 78 apiaries belonging to other beekeepers stand within a 10km/6 mile radius of my apiary. However, I have stopped using chemical varroacides other than organic oxalic and formic acids which do not cause resistance in varroa as the other chemical preparations do with continued use.

What Harm is Caused?

There are many problems and harm is caused at individual bee and colony levels. Both pupae and adult bees suffer cuticular damage as varroa pierce holes in the their bodies in order to tap into food supplies sucking the fat body tissue out of the haemolymph. The recent study: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1009075 published this week shows how varroa use an enzyme called chitinase in saliva to keep open the wounds. This makes for easy entry of viral and bacterial infections into the bee body.

Another recent study shows how deformed wing virus and varroa live together in harmonious symbiosis whereby they both flourish in the presence of the other. You can see how it happens here. I’ve recently subscribed to this useful resource: Inside The Hive.TV which was created by Dr Humberto Boncristiani a scientist currently working in Florida. He has recorded interesting interviews with several well known scientists and beekeepers including Randy Oliver who has done a lot of work on varroa and treatments.

Smaller Bees.

Feasting on fat body tissue by varroa causes weight loss and a reduction in protein levels in honey bees. There is a 7-10% reduction of weight in adult bees due to varroa with adverse affects on nurse bees. The worker bees have a 15% reduction in hypopharyngeal gland activity as a result of protein loss and this impacts negatively on brood and queen feeding activities. Later it will impact on conversion of nectar to honey because the enzymes required for the conversion are produced in the hypopharyngeal glands. Nurse bees may have to become foragers earlier to cope with the imbalance caused by varroa infections and early bee deaths. When wings become shrivelled and crumpled from deformed wing virus the bee is useless to the colony. Affected bees have shorter abdomens and shorter life spans. The latter impacts winter bees and their colony’s ability to survive winter.

More next week.