Let’s say you have a brand new colony of bees that is guaranteed to be uninfected by Varroa mites. How does your colony become infected and how fast do the mites reproduce? Let’s take it from the top:
- One fine spring day one of your bees shares a flower with an infected bee from another colony. Busy doing what bees do, they rub against each other as they seek nectar or pollen and, bingo, a phoretic mite (a mite taking a ride) passes from the foreign bee to your bee.
- Your bee flies home with her load of goods: two full pollen sacks and a gravid (pregnant) female Varroa mite. You are toast.
- Once in the hive, the mite jumps off her ride and cases the joint. She breathes in luscious smells—larvae in their fifth day of development, just ready to be capped. She especially likes the smell of those drone babes, but there are so many cranky bees around, she decides to crawl into a worker cell before the bees have a chance to cart her away.
- She scuttles down to the bottom of the cell and submerges herself in brood food with only her breathing tube breaking the surface. She hunkers down and waits, a mite at the end of the tunnel. Patience, she knows, is a virtue.
- Eventually the immature bee consumes the brood food and the female mite crawls free.
- Meanwhile, the honey bee larva has transformed into a pupa and the mite pierces her soft young body and feeds, vampire-like, on the bee’s hemolymph (blood). Yum. Slurp, slurp.
- The mite feeds for about 60 hours, building her strength for the business of egg-laying. The first egg she lays is haploid, meaning it has only half of a full complement of chromosomes. This grows into a small but mighty male mite.
- Then, once every 30 hours, she lays another egg. All of these subsequent eggs are diploid, meaning they have a full set of chromosomes and are female.
- All the mites go through a series of stages: larva, protonymph, deutonymph, adult. As adults, they mate while still within the capped cell. After the male mite mates with his sisters, he dies. Good riddance, but the damage is already done.
- The female mites continue to live off the female worker bee until she emerges from her cell. These mites are then carried about the hive where they smell those piquant five-day-old larvae. When they get to feeling frisky, they jump off their steed, crawl under a larva, and prepare to start a family of their own.
- But now, instead of one gravid female mite, you have 2.2 gravid females. (Okay, from a practical point of view, it’s just two. But the 0.2 becomes statistically significant as the population builds. Simply put, every fifth cell yields 3 gravid mites.)
The time spent in the larval stage varies bee-by-bee, which is why some cells produce more mites than others. And the drone larval stage is naturally longer, so each drone cell can produce more mites than a worker cell. Nevertheless, the actual number of reproductive mites produced per cell is smaller than the theoretical number because not all eggs are viable and not all mites are able to reproduce. Thank heavens there is something on our side.
Still, the increase in mite populations is staggering, and it doesn’t take long for a colony to become overwhelmed. And anything that increases the time honey bees spend in the larval stage—such as some pesticides—can dramatically and quickly increase the Varroa mite load.