Nov. 10, 2004 — Tropical honeybees and other warmth-loving insects are continuing to challenge the idea that a "nuclear winter" enshrouded the Earth for years after the asteroid impact that killed the dinosaurs 65 million years ago.

The survival of the tropical honeybee Cretotrigona prisca beyond the gigantic end-Cretaceous extinction is a sure sign that it could not have been cold for long, said University of New Orleans graduate student Jacqueline M. Kozisek.

She presented her ideas on the matter Monday at the meeting of the Geological Society of America in Denver.

"These tropical honeybees were very, very close to modern tropical honeybees," said Kozisek.

So close that those preserved in amber might have had similar limits to how much cold they could stand. They might also have been the ancestors of today's tropical honeybees, she said.

Today's tropical honeybees thrive at 88 to 93 degrees Fahrenheit (31-34°Celsius), according to entomological researchers, Kozisek said. The same goes for the flowering plants off which they make their living.

If modern tropical honeybees are any measure, any post-impact cooling from debris blocking sunlight could not have lowered temperatures more than 4 to 13 degrees (2-7°C) without rubbing out bees. Current nuclear winter theories from the Chicxulub impact estimate drops of 13 to 22 degrees F (7-12°C), too cold for tropical honeybees.

"We know that countless other lineages of tropical plants, insects, fish and reptiles also survived," said paleontologist Peter Wilf of Pennsylvania State University. "The asteroid didn't kill everything everywhere, or we wouldn't be here today."

In recent years, paleontologists have been gathering increasing evidence that the event that killed off 70 percent of species 65 million years ago was very selective, Wilf said.

One recent study calls on a massive heat pulse caused by debris reentering the atmosphere after being shot into space by the impact at Chicxulub, he said. Such a blast of heat would have only lasted a few hours and killed only organisms unable to hide in water or other shelter.

For that reason, the news of tropical honeybees surviving comes as no surprise, Wilf said.

Kozisek conducted her study by searching the paleontology literature for information about organisms that appears to have survived the extinction event. She then picked out tropical honeybees because they had almost indistinguishable modern relatives and a narrow temperature range.