It’s been raining every day for a week; some days solidly. The oak at the bottom of the garden still holds onto a few green leaves while all the other deciduous trees around are bare. The river Nairn is almost bursting its banks and small streams and ditches along the side roads are debris-clogged and overflowing. You can see a big puddle in the field above forming a large pond now frequented by gulls. The farmer is disappointed that previous attempts at drainage have failed, and the wintering sheep from the grouse moors are pushed over to the other side of the field.
Calendar Girl Connie.
The wee bee apprentice is missing the bees but we will be making candles tomorrow and finding out more about bees wax. She’s quite excited about featuring in Vita-Europe’s calendar again this year. Check out August in the new 2021 Vita-Europe calendar. The bee suit came from my favourite supplier in the US: http://hudsonvalleybeesupply.com/
https://mailchi.mp/e7fafe2ebc13/vita-bee-health-newsletter-december-2020?e=cc9aaa0fcd
European Honey Bees Resistant to Varroa destructor.
A new paper published 2 days ago on 8th December 2020 grabbed my attention this week and raised some hope.
A Close Look at Varroa.
Varroa (Varroa destructor) is not an insect. It belongs to the order: Mesostigmata, class: Arachnida, and family: varroidae. It is a parasitic mite and more closely related to ticks and spiders than to insects.
The Life Cycle.
The life cycle comprises two stages: the phoretic stage and the reproductive stage.
The varroa you see in the photo above (riding on the bee foraging among wild thyme) is a female mite as are all varroa found outside the brood cell. It is in the phoretic stage of the life cycle which means that it is traveling around looking for a way to enter a brood cell to reproduce. She has already mated with her brother, in the cell they were produced in, and she came out of the cell on an newly emerging bee. This one moved across to a forager at some point and left the hive.
In the phoretic stage, she feeds on the adult bee through a tiny hole that she has pierced with her mouthparts, usually on the underparts of the bee between the ventral (front) sternites which are the cuticular plates that comprise her waxy waterproofed exoskeleton. The tergites are the plates on her back or dorsal area. Mostly, varroa are tucked away and hidden so you don’t usually see them unless infestation levels are high. This mite will spread viruses from adult bee to adult bee in this way. An enzyme in her saliva will keep the tiny feed hole open and this promotes entry of viruses and bacteria which will travel round the bee body in her haemolymph. The varroa will feed on fat body tissue which is abundant under the dorsal and ventral cuticular surfaces of the bee.
Spreading.
The varroa in our photo is not currently feeding on the bee because it is waiting for an opportunity to jump across to another foraging bee, perhaps from another beekeeper’s colony. In this case, it was disappointing to find varroa in one of Scotland’s most beautiful and remote parts of the west coast where there are still varroa-free pockets of land. How quickly it spreads by foraging, robbing, swarming and drifting. It also spreads by ignorance; new unknowing beekeepers excited by the prospect of getting their first bees can’t wait for local stock and buy bees from a supplier who doesn’t care if they send varroa to areas of Scotland currently free of the mite.
Vital Statistics.
You can see that the adult female varroa is larger than the male. They are all eyeless and blind. The male never leaves the cell and dies after his mating role is over. He mates with his sister by the way. He doesn’t develop the reddish brown colour of his sisters but remains a light yellow colour. He is about 0.75mm x 0.70mm and almost spherical in shape in comparison to the crab-like oval-shaped female who is dark red in colour after the last moult. She has a flattened body of about 1.2mm x 1.7 mm and weighs around 325 µg in the phoretic stage, and 480 µg when gravid and full of eggs during the reproductive stage in the cell.
The varrroa mite has 4 pairs of legs and the first pair is thought to play a role in the sensory nervous system. The mite can taste and smell via receptors in these legs, and the other legs are involved in ambulation. The mouthparts are formed by the gnathsoma, and the idiosoma comprises the hard sclerotized shell on the back and areas on the front of the mite giving it the crab-like appearance. There are good images in the following document from BeeBase. file:///C:/Users/ann/Downloads/APHA_Managing_Varroa_2020_ELECTRONIC_ONLY.pdf
Next week we will take a look at the reproductive stage.