Earthwatch teams to research impact of Hurricane Katrina on Louisiana caterpillar populations. Climate change may spell disaster for agricultural crops and forests, in the form of caterpillar outbreaks, according to a paper published this week in the Proceedings of the National Academy of Sciences. The paper links increasing climatic unpredictability, including extreme storms such as the recent Hurricane Katrina, to decreasing levels of parasitism by wasps and flies that control caterpillar populations.
"This finding is potentially very significant," said Dr. Lee Dyer, an ecologist at Tulane and Principal Investigator of Earthwatch Institute's Forest Caterpillar project, who is a co-author of the paper. "It could mean that the parasite services that we take for granted may start declining as climate change drives more of these extreme weather events. Because parasites are a key regulator of insect herbivores, we speculate that damaging outbreaks in natural and agricultural systems will become more common."
Many animals have a strong dependence on environmental cues, and scientists predict that climate change may adversely affect these animals' behaviours. Such effects are likely to be more pronounced in predators, as these animals have to cope with both changes in climate and subsequent changes in the behaviour of their prey. The same could be said of the parasitic wasps and flies that play an important role in controlling insect pest populations.
The authors used caterpillar parasitism data from 15 insect-rearing programmes ranging from Canada to Brazil, comparing these data with annual rainfall variations for each region. They found that the overall frequency of parasitism against caterpillars decreased as climatic variability increased. No other environmental factors measured accounted for this pattern, suggesting that unpredictable rainfall patterns are disrupting the ability of parasitic wasps and flies to infest their prey.
The PNAS paper included data from Dyer's caterpillar-rearing programmes at La Selva, Costa Rica and Yanayacu, Ecuador, supported by the efforts of Earthwatch teams. It also included data from Arizona and Louisiana, where Dyer has recently expanded his Earthwatch teams to explore caterpillar parasites still further.
"We could not have collected data at La Selva and Ecuador without Earthwatch volunteers," said Dyer. "For most years over the last decade, our Earthwatch funding was the only financial support we had for this project."
New Earthwatch teams added to New Orleans, Louisiana, the site of Dyer's lab at Tulane, will examine parasitism on caterpillars in systems affected by Hurricane Katrina, with findings very relevant to the present paper.
"They will also be working with our insect collection, which provides more specific data for looking closely at these interesting relationships," added Dyer.