Altruistic suicide against Varroa

The parasitic mite is decimating beehives. Biologist Paul Page has shown that an Asian forager has found a countermeasure through a system of “altruistic suicide.” A model that its European cousin could follow?

It runs, it runs, the varroa. It even flies. This mite, from the same family as ticks, actually moves on adult worker bees, clinging to their necks or hiding in the folds of their abdomens. It then pierces a hole in the cuticle, draws some haemolymph to obtain nutrients, and in doing so transmits diseases: “Of the some twenty viruses identified in bees, most are associated with the presence of Varroa destructor,” explains biologist Paul Page.
Once inside the hive, varroa infiltrates the cells of larvae that are fed royal jelly by young workers and subsequently sealed with a wax cap. The mite takes advantage of the roughly twenty hours preceding cell capping to jump from a worker, enter a cell, and hide beneath the larva. Once the cell is sealed, “it pierces the larval skin, begins feeding on its haemolymph, and transmits diseases that weaken it even before it becomes an adult.”
The intruder in the cell is always a gravid female, which lays her offspring there: “The first egg is usually a male, while the three or four that follow develop into female varroa mites. The male then inseminates his sisters, which can leave the cell when the worker emerges 10 to 11 days later.” This means that within three weeks the varroa population in a hive can double or even triple—“an increase that becomes exponential over the season if nothing is done to treat the colony against this parasite.” Varroa is thus one of several causes contributing to the bee mortality observed in recent years.
Last year, Paul Page published in the journal “Scientific Reports” the results of a three-year study conducted in China and Thailand on the parasite’s original host, the Asian honey bee (Apis cerana). It should be noted that the European honey bee (Apis mellifera) has been infested by Varroa destructor for only about a century.

The immune system under threat

In addition to transmitting pathogenic viruses, the presence of varroa also weakens the colony’s immune system. “Bees are debilitated by the parasite, more frequently exhibit deformed wings, and can no longer fly, thereby reducing the amount of food brought back to the hive; the decline is gradual, but a colony heavily infested with varroa cannot survive more than a year without the help of a knowledgeable beekeeper,” explains Paul Page.
When varroa arrived in Europe in the 1980s, beekeepers initially turned to chemical treatments using synthetic acaricides. “At first this worked well, but the parasite quickly developed physiological resistance to these products.” Today, more natural products based on formic and oxalic acids, as well as plant-derived compounds, are used.

A promising study

The study conducted by Paul Page and his colleagues at Agroscope and the University of Bern nonetheless opens up new perspectives.

A defence through hygiene

Because this “altruistic suicide” and this hygienic behaviour are behavioural traits, they must have a genetic basis. Through selective breeding, it should therefore be possible to obtain European honey bee colonies in which these traits are reinforced.

Source: https://www.migrosmagazine.ch/abeilles-contre-varroa-mortel-combat

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Altruistic suicide against Varroa

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