Pahndeepah Perceptions

Throughout North America, honeybees are abandoning their hives. The workers are often found dead, some distance away. Meanwhile, the hives are like honeycombed Marie Celestes, with honey and pollen left uneaten, and larvae still trapped in their chambers.

There are many possible causes of this “colony collapse disorder” (CCD). These include various viruses, a single-celled parasite called Nosema apis, a dramatically named mite called Varroa destructor, exposure to pesticides, or a combination of all of the above. Any or all of these factors could explain why the bees die, but why do the workers abandon the hive?

Andrew Core from San Francisco State University has a possible answer, and a new suspect for CCD. He has shown that a parasitic fly, usually known for attacking bumblebees, also targets honeybees. The fly, Apocephalus borealis, lays up to a dozen eggs in bee workers. Its grubs eventually eat the bees from the inside-out. And the infected workers, for whatever reason, abandon their hives to die.

There are hundreds of species of Apocephalus flies, and they’re best known for decapitating ants from the inside. The larvae, laid within an ant, migrate to the head and devour the tissue inside. The brainless ant wanders aimlessly for weeks, before the larvae release an enzyme that dissolves the connection between the ant’s head and body. The head falls off, and adult flies emerge from it.

A. borealis has a similar modus operandi, but it targets bees not ants. Core discovered its penchant for honeybees by sampling workers that had been stranded in the lights of his faculty building, and other locations throughout the San Francisco Bay area. The fly was everywhere. It was parasitizing bees in three-quarters of the places that Core studied, and its DNA confirmed that the species that attacked honeybees was the same one that kills bumblebees.

When Core exposed honeybees to the flies in his lab, he saw the same events that befall unfortunate ants. The flies lay eggs in a bee’s body and weeks later, larvae burst out from behind the insect’s head. It’s no surprise that the infected bees, with up to 13 larvae feasting on their brains, seem a little disoriented. They walk round like zombies, pacing in circles and often unable to stand up.

They also abandon their hives. Core found that the dying insects literally head towards the light. Large numbers of them become stranded within bright lights. Many flying insects show a similar attraction, but the stranded bees were stock still rather than buzzing about. They would also head towards lights on cold, rainy nights when other insects seek shelter.