Washington, October 6 (ANI): A long-term study has shown that El Nino, a global climate pattern, drives Sulfur butterfly migrations across the Panama Canal.

Climate change has been linked to changes in the migration of butterflies in North America and Europe but this is one of the first long-term studies of environmental factors driving long-distance migration of tropical butterflies.

For 16 years, Robert Srygley, a research ecologist at the US Agricultural Research Service, and colleagues, tracked the progress of lemony yellow Sulfur butterflies, Aphrissa statira, a species found from Mexico to Brazil, as they migrate across central Panama from Atlantic coastal rainforests to the drier forests of the Pacific coast.

“The El Nino Southern Oscillation-a global climate cycle-turns out to be the primary cause for increases in the plants that the larvae of these butterflies eat. El Nino results in dry, sunny days in Panama, which favor plant growth. When the plants prosper, we see a big jump in the number of Statira Sulfur butterflies,” said Srygley.

Peak Sulfur butterfly migrations take place a month after the rainy season begins in Panama.

Because butterfly development-from egg to larva to pupa to adult-takes about 22 days in the laboratory, Srygley thinks that these butterflies lay their eggs on new leaves produced by vines only four or five days after the rains begin.

His team tracked the production of new leaves by two of the butterflies’ host plants for 8 years. Drier years resulted in more new leaves.

The number of migratory butterflies was greatest in El Nino years, with one exception.

The El Nino Southern Oscillation is a global-scale climate phenomenon characterized by changes in sea surface temperatures.

In Panama, El Nino years have less rainfall during the dry season and higher plant productivity, with the one exception being an unusually wet El Nino year.

The lowland forests of Panama fall into a set of habitats encircling the globe in which insect migrations are larger during El Nino years.

However, the Panamanian wet forest is in a class of forests that have the greatest abundance and diversity of herbivorous insects in the world.

“It is like we had seen the tip of the iceberg and suddenly we realize its true size”, Srygley suggested.

The authors predict widespread insect migrations during El Nino years.

According to Srygley, “Understanding how global climate cycles and local weather influence tropical insect migrations should ultimately improve our ability to predict insect movements and effects such as crop damage.” (ANI)