Climate changes may make insects winners.

While many people fear global warming, insects should probably celebrate it, a new study indicates.

If changes in Earth's climate continue to bring day and evening temperatures more in line with one another (SN: 1/4/92, p.4), insects may find themselves less troubled by plant toxins, according to a study comparing growth rates of tobacco hornworms living in either fluctuating or constant temperatures.

Researcher Nancy E. Stamp of the State University of New York at Binghamton exposed tobacco hornworm caterpillars to either a steady [20 degrees C] environment or to a temperature that alternated between [23 degrees C] for 15 hours and [15 degrees C] for 9 hours. She fed them either a standard diet or one doctored with rutin, a plant toxin that wards off insects and other plant pests.

The different concentrations of rutin in the feed covered the range found in one of the tobacco hornworm's common meals - tomato plants - Stamp reports in an upcoming ENTOMOLOGlA EXPERIMENTALIS ET APPLICATA.

At higher concentrations, rutin hindered the eating and growth rates of caterpillars living in the variable temperature. But at a constant temperature, the rutin failed to have this effect.

"It didn't matter how much more toxin was in the diet, [the caterpillars] acted like there was no toxin," Stamp says.

Typically, plant toxin experiments are done at one temperature, says Frank Slansky at the University of Florida in Gainesville. Stamp's work indicates that "much of [this] prior work may not reflect biological reality," he adds.

This study carries "an important message about the interactive effects of [plant toxins] and temperature under field conditions," Stamp writes. Data from the last 40 years reveal that the average annual minimum temperatures have risen, while maximum temperatures have not changed. "We are not paying any attention to the fact... [that] this may interfere with plants' abilities to defend themselves," she says.

The interaction between other insects and plant toxins exposed to steady temperatures would likely be similar to that seen with hornworms, Stamp predicts.

But, warns Slansky, "We must be cautious not to overgeneralize from these results." The poison-resistance mechanisms of insects vary widely, and plant toxins have diverse modes of action, he explains.