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Northern Spring and Varroa

By Matthew Kobe, SBGMI Science & Research Chair

While we are all getting excited about spring and the start of the bee season, it is important not to forget about the virus-spreading assassin who is also excited for the new season: the Varroa mite. As our bees start to brood up and increase in numbers, so too do the Varroa mites. One of the most significant factors in determining the potential damage that will be caused by Varroa throughout the bee season is the number of mites that your colony starts with in the spring. Because Varroa reproduces exponentially, a small Varroa population can explode very quickly. Here are some things to consider depending on what type of colonies you are starting with this spring.

  1. Overwintered colonies – These colonies will likely need to be split in the spring to prevent them from swarming. This is a perfect time to monitor for mites and treat if necessary. Before you split, you should consider doing a mite wash. If your colony washes above the threshold, you will want to address the problem and intervene with a Varroa solution as soon as possible (this guide will help with your decision). The best way to do this during the spring is in tandem with a brood break caused by splitting. You can move the queen and open brood to a nuc box.  By moving the queen and only open brood, you are ensuring that all mites within the colony are phoretic as there is no capped brood for the mites to hide in. You can then treat the nuc box with a miticide of your choice (we would recommend oxalic acid) to kill the majority of the mites. As for the parent colony that will be queenless and contain the capped brood, it will experience a brood break as it goes through the requeening process. Depending on how you requeen the colony (queen cell, virgin, mated queen, let them make their own), you will have a period of time after 21-24 days where all the brood from the previous queen will have emerged, resulting in no capped brood. Once again, if there is no capped brood, this means that all the mites are phoretic and vulnerable to miticides. This is the BEST time to intervene, again this guide can help you make the best decisions (this guide will help with your decision); though at this juncture, oxalic acid is extremely effective.  By following this process, you can ensure that your parent colony and daughter colony start the year with a low infestation rate of Varroa mites.
  1. Nucs – If you are in the market for a nuc or have one on order, we recommend asking the seller a couple of important questions. Where is the nuc coming from and how did they manage their mites? The location of the nuc is important because if the nuc is coming from a warmer climate (California, Georgia, Florida, etc.) the colony that the nuc was made from will have been brooding up for quite some time. As mentioned above, if the bees are brooding up and increasing in numbers, so are the Varroa mites. Additionally, when nucs are created, the seller generally includes frames of capped brood. Unfortunately, the majority of the mites within a colony are found under the cappings on the brood. This means that your new nuc may come with a high Varroa mite population.

    Alternatively, if you are purchasing Michigan overwintered nucs, the bees have only just begun brooding up. Thus, the odds of getting a nuc that has a high Varroa count are reduced. This is just one of the many reasons why we recommend purchasing overwintered Michigan nucs from a local beekeeper. However, just because you are buying an overwintered Michigan nuc, does not mean you are in the clear. It is still important to ask the seller how they managed mites throughout the year, specifically in the fall and winter. If they treated their colonies with oxalic acid in the fall or winter while the colony was broodless, it is likely that they achieved a very efficacious mite kill and their nucs will likely come with very few mites. However, if they did not treat in the fall or winter, it is possible that their bees overwintered with mites and these mites will have been reproducing with the bees as they have been brooding up in the spring, resulting in increased Varroa numbers.  
  1. Packages – While we do not recommend anyone purchase packages (for several reasons that we may write about later), they do come with a “silver lining.” Because packages do not come with any brood whatsoever, this ensures that any mites are phoretic and vulnerable to an oxalic acid treatment. After the queen starts laying her first eggs, you will have 8-9 days before the bees will start to cap the new brood. We recommend treating the colony with oxalic acid prior to this capping to ensure the majority of mites are killed before they are able to reproduce. Some people recommend treating the packages shortly after installing them. We would discourage this practice as bees without brood are more likely to abscond. Instead, we recommend waiting to treat until the bees have some open brood. Colonies with open brood, are significantly less likely to abscond. 

In any case, it is always best to do a mite wash so you know the starting infestation rate of your colony.  It is important to continue these mite washes throughout the year to ensure your infestation rate is under the threshold level in your area. Just because you don’t see mites on your bees, does not mean they aren’t there. The majority of the mites will be under the cappings as they feed and reproduce on the developing brood. The mites that are phoretic prefer to be on the underside of bees as they feed on their fat bodies. Thus, you likely will not see any Varroa mites while completing a hive inspection unless you are picking up several bees and checking their bellies. If you do see mites crawling on the comb or on the backs of bees, you should perform a mite wash immediately as these are signs that your colony is experiencing a heavy infestation of Varroa mites. Remember, continued monitoring is key.

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