Dying for change


By Kurt Kleiner in Baltimore WHILE rising levels of atmospheric carbon dioxide might make plants grow faster, they could be bad news for plant-eating insects. A Florida biologist has found that subtle increases in CO2 can kill leaf-eating moths by reducing the nutritional value of the leaves they feed on. Peter Stiling, a biologist at the University of South Florida in Tampa, says the new research contributes to the mounting evidence that the ecological changes brought about by increasing CO2 levels are likely to be hard to predict. “It looks like elevated CO2 has at least as many direct effects as indirect effects,” he says. Stiling looked at several species of mining moths, whose larvae tunnel through leaves for food. By examining the tunnels, or “mines”, they left behind, Stiling and colleagues could tell whether the larvae had died inside the mine, were killed by predators such as spiders or ants, or were eaten from the inside out by the larvae of parasitic wasps. Stiling conducted the experiment at the Kennedy Space Center in Florida in 16 open-topped chambers containing myrtle oak and sand-live oak. Half of the chambers had normal CO2 levels, while the other half had approximately double the normal level of CO2. Stiling found that many more larvae died in the chambers with high CO2 levels. About 10 per cent of the larvae in the high CO2 chambers died inside the mines, compared with only 5 per cent in the chambers with normal CO2 levels. The deaths within the leaf mines probably resulted from malnutrition, Stiling says. Plants in high CO2 conditions grow bigger and faster, but their lower nitrogen content makes them poorer nutritionally. Many more high CO2 larvae fell victim to parasites as well. Stiling says the reason is probably related to poor nutrition. Larvae in high CO2 plants had to eat more leaf in order to get enough food to mature. Stiling says the bigger mines might have been more obvious targets for parasitic wasps, and the increased amount of time the larvae spent in the leaves made it more likely that they would be found. Also, malnourished larvae might have been more susceptible to the parasites, he says. More on these topics:
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