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Infertile varroa or bees have removed the offsprings ?

Good morning everyone,
I'm Erica, a beekeeper from Italy. I would like to ask you a question. I found 250/300 operculated cells reopened with a red-eyed pupa inside. This when i blocked the brood on a moveable panels of silkworm eggs, after 21 days (to unlocking the queen). On 50 cells examinated, after extracting the pupa i found just 1 varroa without offsprings inside.
Someone could explain why this happened? Infertile varroa or bees have removed the offsprings?
Thank you

Comentarios

This is a very intersting story can you elaborate a bit more, I am very intrested in this.

I can add:
1) that the family had no symptoms of crisis, everything was in order
2)After the brood has been blocked and treated i found a fall of 400/500 varroe (25% of varroe touched by bees, under the treatment)
It's the First time that It happens. Now i'm waiting for the brood to mature and then i'll check again to see the situation.

The "strange" behaviour Erica found in her colonies is a general property of honey bees. Some have it very little, some more. It is considerred the key to the varroa problem.

Please find my comment and info from the internet in the pdf file.

Dear Erica,

I am Jorge Rivera Gomis, I am veterinarian and I work in the Beekeeping Laboratory of the IZSLT in Rome (Italy). Regarding the question you asked, I can give you some information about the effects of brood interruption for varroa control in European honeybee colonies that I hope will be useful for you.

The objective of causing a period without presence of bee brood in the hive (brood interruption period) is to force the varroa mites to stay on the adult bees outside of the brood cells. This condition will make all the varroa mites vulnerable to a treatment with an acaricide (e.g. oxalic acid, thymol, amitraz, etc.), as they cannot be protected inside the bee brood cells, where the varroa mite enters to reproduce and complete its life cycle. Therefore, combining a brood interruption period with an acaricide treatment will boost the acaricidal efficacy (until around 90% efficacy) (Rosenkranz et al., 2010, Giacomelli et al., 2015), protecting our bees from the effects of the varroa mite infestation. Please, take into account that only registered and safe products should be used to treat honeybees against varroa, and the instructions for its use should be always followed in order to ensure the efficacy and safety of the treatment. The use of the brood interruption period alone has also acaricidal efficacy (around 40%) (Giacomelli et al., 2015, unpublished data), but its combination with a proper treatment with an acaricide boosts its effect (until around 90% efficacy).

In order to produce the brood interruption there are different techniques:

-Brood removal: You can remove the frames with brood making sure that the queen remains in the beehive with the majority of adult bees, and then you can apply an acaricide in absence of brood. You can form nucs with the removed brood frames and treat them with a product effective on the varroa inside the brood (formic acid based products), or you can wait until a new queen is born in those nucs and perform another treatment in absence of brood. Please, note that all the hives present in one apiary should be treated at once, so you should place those new nucs (that will have a high level of infestation due to the hatch of the varroa present in the caped brood) in a different location several kilometers away from the original apiary.

-Queen caging on a comb (Figure 1): Caging the queen on a comb will allow the queen to continue laying eggs (but only in that comb), while the rest of the combs will become broodless. You should remove that comb the 20th day, before any bee hatches, and you should treat the day 21 (if there was no drone brood) or the day 25th (if drone brood was present) with an acaricide (we usually advice to treat with oxalic acid, which has a high efficacy in absence of brood).

-Queen caging on a cage without possibility of laying eggs: Caging the queen in a cage that does not allow her to lay eggs totally interrupts the presence of brood in the hive, leaving the varroa mites without a shelter and vulnerable to an acaricide treatment. The cages used for this purpose are similar to the one shown in Figure 2, that have small entrances that allow the worker bees to come and go but do not allow the queen to get out (because the queen is bigger than the workers and cannot pass through those holes). The queen should be freed the 21st day of caging if there is no drone brood and the 25th if there is drone brood. The acaricide treatment should be applied the same day that the queen is freed.

Figure 2- Queen caged inside without possibility of laying eggs.

Please, note that if you apply properly the explained techniques, there shouldn’t be brood in the hive after the treatment finishes. If you treat properly and following the label instructions with an acaricide during the broodless period (e.g. oxalic acid, thymol, amitraz, fluvalinate) the efficacy should be very high and you should not find varroa.

If you continue finding high levels of varroa it means that something went wrong and the efficacy of the treatment was low, and you should repeat the treatment properly.

You can find more information about the varroa mite cycle in the following links to videos:

-https://www.youtube.com/watch?v=wj-h5VJqaoI

-https://www.youtube.com/watch?v=G9-FGA3bwEw (This one is made with real footage, but you should activate the captions in English, as the audio is in German)

You can find more complete information about the varroa life cycle and ways of control in the following scientific papers:

 Rosenkranz, P., Aumeier, P., & Ziegelmann, B. (2010). Biology and control of Varroa destructor. Journal of invertebrate pathology, 103, S96-S119.

Giacomelli, A., Pietropaoli, M., Carvelli, A., Iacoponi, F., & Formato, G. (2016). Combination of thymol treatment (Apiguard®) and caging the queen technique to fight Varroa destructor. Apidologie, 47(4), 606-616.

Please, tell me if I did not answer completely to your question or if you have any more doubts.

Thank you and best regards,

Jorge Rivera Gomis