The Microscopic Spines That Many Bee Species Use to Hatch
Perhaps you’ve seen the 2015 video from photographer Anand Varma (and shared again last week via National Geographic), a time-lapse of bee larvae hatching and growing in their cells:
Watch: larvae grow into bees in this mesmerizing time-lapse https://t.co/JvRbXDMl2e
— National Geographic (@NatGeo) July 19, 2017
What you can’t see in that video—in fact, what scientists couldn’t see until they put some bee larvae under scanning electron microscopes about a decade ago—are the miniscule body parts that help first-instar bee larvae break free from their eggs in the first place.
In a research paper published today in the open-access Journal of Insect Science (JIS), researchers share the most comprehensive analysis yet of what they call “hatching spines” found on the larvae of a wide variety of bee species. The tiny spike-like structures appear to serve as both a mechanism for breaking open the larva’s egg and a release point for enzymes that aid in disintegrating the egg material.
“While studying specimens of a species of the bee genus Svastra collected in Florida in 1964, I was surprised to discover one egg that revealed a shiny stripe along both sides of the sausage-shaped egg as the larva was hatching, which contrasted with the rather dull white chorion elsewhere on the egg or on any other eggs of the species,” says Jerome G. Rozen, Jr., Ph.D., curator of the Apoidea Collection at the American Museum of Natural History (AMNH) in New York and lead author of the new study. “What was it? What was its function? It was so different from anything that I had seen before, I remembered it for a long time.”
Fast forward to 2006: Rozen and fellow researchers examined egg hatching in bees of genus Monoeca under a scanning electron microscope (SEM) and found that what looked like “granules” above the spiracles were in fact extremely small, sharp spikes. A first-instar bee larva is just 2 millimeters long, approximately; the individual spines measure just 3 micrometers from base to tip—in range of the size of a single bacterium. In the time since, Rozen and colleagues have found these same “hatching spines,” as they call them, in four of the seven families of bees.
In the new research in JIS, Rozen, AMNH colleague Corey Shepard Smith, and James H. Cane, Ph.D., of the USDA Agricultural Research Service explore in detail the presence of hatching spines and how they differ among various bee species:
- In solitary and some cleptoparasitic bees, the spines appear in a row along both sides of the body of the first-instar larva, just above the spiracles. During hatching, the egg chorion splits on both sides of the body along this line.
- In honey bees, the hatching spines appear as a cluster, rather than a line, though again just above the spiracles along the body of the larva. In hatching, however, the egg chorion is disintegrates more thoroughly.
In both cases, the researchers suspect the bee larvae release an enzyme to dissolve the egg material, and that the spines and enzyme work in tandem in the hatching process. SEM images of the spiracles located near the spines show “spheroids” that Rozen and colleagues posit are droplets of a hatching enzyme, though this is an area in need of further research to be sure.
Rozen says he hopes to continue studying bees hatching mechanisms in further detail to answer some of the questions raised by research so far: “How widespread is this phenomenon of hatching spines? There are a total of seven families of bees: four down, three to go. And do all bees have hatching spines? No. We know for a fact that, in the Apidae, certain cleptoparasitic bees do not have them, which presents another question: How do those bees extricate themselves from their egg chorions?”
Journal of Insect Science