Back-Seat Driver: The Parasite That Makes Bees Drop Off Its Babies
By Paige Embry
From a human perspective, insects are odd, odd creatures. Some display the wonder of complete metamorphosis, allowing us to simultaneously love nectar-sipping butterflies and fret over their leaf-eating caterpillar offspring. We marvel at strange or seemingly impossible ways of life: dung-rolling beetles, reproduction with no males required, death by sex for honey bee males. And near the apex of oddness are the strepsipterans, aka the twisted-wing insects.
Strepsipterans parasitize a wide array of other insects. The males are free-flying but the females of many species achieve independent mobility only as first instar larvae—which is when they seek out a host to live within for the rest of their lives. The females don’t develop into “typical” adult insects—they have no wings, no legs, no eyes—but they are fertile and manage to mate even though they live inside another insect. These females have a brood canal (also the mating portal) and they stick the body part that has that canal outside the host and release a pheromone, calling the males to them. Adult males live for only a few hours, and that time is all about finding and mating with one of those protruding body parts. A new study published in the Journal of Insect Science shows that at least one species of strepsipteran, Halictoxenos borealis, also seems to have a super-power—mind-control of its host insect.
The study looked at the behavior of Lasioglossum apristum, a bee parasitized by Halictoxenos borealis. Yuta Nakase, Ph.D., a postdoctoral researcher at Shinshu University in Nagano, Japan, says he chose this project after seeing parasitized L. apristum visiting hydrangeas, which have no nectar and therefore provide only pollen rewards for visiting bees. Since adult female bees usually collect pollen to feed offspring and not themselves, Nakase realized this behavior didn’t make sense, because one of the side effects of being parasitized by H. borealis is that L. apristum have no offspring.
“I had a hunch that something strange would be happening and decided to do some research,” says Nakase.
Nakase and colleague Makoto Kato, Ph.D., of Kyoto University, developed a study to try and determine if H. borealis affected the behavior of the L. apristum bees not merely by their presence but via active manipulation of the host’s behavior—or, put another way, mind control.
The scientists studied the actions of parasitized and unparasitized L. apristum bees on Hydrangea serrata. They found both kinds of bees walked around, neither bothered to look for nectar, and neither ate any pollen (none was found in their guts). But the behavior of the two types of bees differed in one significant way: Unparasitized bees actively collected pollen to take home to their larvae, while the parasitized bees collected none. Instead, a parasitized bee curled its abdomen and pressed the top against the leaf—making it easier for the parasites to offload their larvae. (Rather than laying eggs, H. borealis females release first instar larvae.) Unparasitized bees did not engage in this activity.
The researchers say that this behavior was “evidence that strepsipteran parasites can alter the behavior of individual bees by changing their flower-visiting objective and corresponding behavior from pollen collection to the release of first instar larvae.”
Nakase says that he’d like people to know more about the importance of parasites. “From the perspective of biodiversity conservation and agricultural productivity, it is important to understand the parasites are involved in the pollination symbiosis system, but we do not know enough about them,” he says.
Parasites may have a bad reputation, and a lot of people might be happy if parasites disappeared from the world, but Nakase isn’t among them—even regarding the parasites that engage in mind control.
“Bee-Parasitic Strepsipterans (Strepsiptera: Stylopidae) Induce Their Hosts’ Flower-Visiting Behavior Change”
Journal of Insect Science
Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.
This is most fascinating. I’ve observed strepsipterans on Polistes, but never on bees, and I’m impressed by the research that revealed this important behavioral modification. I would like to suggest that the substance emitted by the adult female strepsipterans to attract the males is better described as a pheromone than as a hormone.
Thanks, Bob. Yes, that should have said pheromone. That text has been corrected accordingly!