Just no end to destruction

PLANT-EATING insects inhabit all forest ecosystems, but sometimes their numbers explode, resulting in massive tree defoliation. Researchers from the US-based Smithsonian Tropical Research Institute (STRI) have recently reported about a severe moth outbreak related to drought conditions following the 1997-1998 El Niño Southern Oscillation (ENSO) event in a dry lowland forest near Panama’s Pacific coast. Their findings are alarming — if ENSO events become very common due to climate change, repeated herbivore outbreaks might alter forest species composition. Moth larvae devoured 250 per cent more leaf material than usual even as the researchers were setting up an experimental protocol to monitor herbivores and leaf damage of 20 tree species.

“The outbreak was unusual because it involved a dozen insect species and followed a drought associated with one of the most severe El Niño events experienced in the study area,” says Sunshine Van Bael, one of the STRI scientists. What caused the outbreak? Most likely the drought kept the caterpillars’ natural enemies out of play, but the exact cause remains a mystery.

“Our findings do indicate that we should pay attention to these harbingers of climate change. A better understanding of the natural history of these systems may help us predict outbreaks involving crop pests or human disease vectors,” Van Bael concludes.