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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGY AND MANAGEMENT OF GRASSHOPPERS AND OTHER INSECT PESTS IN THE NORTHERN GREAT PLAINS

Location: Pest Management Research Unit

Title: El Niño, host plant growth, and migratory butterfly abundance in a changing climate

Authors
item Srygley, Robert
item Dudley, Robert -
item Oliveira, Evandro -
item Riveros, Andre -

Submitted to: Biotropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 2013
Publication Date: January 6, 2014
Repository URL: http://handle.nal.usda.gov/10113/58334
Citation: Srygley, R.B., Dudley, R., Oliveira, E.G., Riveros, A.J. 2014. El Niño, host plant growth, and migratory butterfly abundance in a changing climate. Biotropica. 46(1): 90-97.

Interpretive Summary: We know very little about the causes of insect outbreaks in the tropics. In the wet forests of Panama, El Niño typically brings a more prolonged and severe dry season. Interestingly, many trees and lianas that comprise the wet forests increase their productivity as a response to more severe and prolonged droughts. We quantified the abundance of migrating Marpesia chiron butterflies over 17 years and the production of new leaves of their hostplants over 9 years to test whether increased abundance of migrating insects and productivity of their food plants are associated with El Niño and La Niña events. The number of migrating butterflies was greatest during El Niño events, which are characterized by higher than normal sea surface temperatures in the equatorial region of the Pacific Ocean. El Niño has a drying effect on the Panama Canal region, and three hostplant species responded to El Niño with greater production of new leaves. In contrast, the number of butterflies migrating was lowest in La Niña years when Pacific Ocean surface temperatures are lower than normal. We conclude that dry season rainfall and photosynthetically active sunlight can serve as primary drivers of larval food production and insect population outbreaks in Neotropical wet forests, with drier years resulting in enhanced plant productivity and herbivore abundance. If climate change brings about a more El Niño-like mean state, tropical forest productivity and abundances of associated herbivores will increase. Insect populations should also closely track changes in both frequency and amplitude of the El Niño Southern Oscillation. Understanding how global climate cycles and local weather influence tropical insect migrations improves our ability to predict the ecological and economic effects of climate change.

Technical Abstract: In the wet forests of Panama, El Niño typically brings a more prolonged and severe dry season. Interestingly, many trees and lianas that comprise the wet forests increase their productivity as a response to El Niño. Here we quantify the abundance of migrating Marpesia chiron butterflies over 17 years and the production of new leaves of their hostplants over 9 years to test the generality of the El Niño migration syndrome, i.e., whether increased abundance of migrating insects and productivity of their food plants are associated with El Niño and La Niña events. We find that the quantity of M. chiron migrating across the Panama Canal was directly proportional to the sea surface temperature (SST) anomaly of the Pacific Ocean, which characterizes El Niño and La Niña events. We also find that the production of new leaves by its larval host trees, namely Brosimum alicastrum, Artocarpus altilis, and Ficus citrifolia, was directly proportional to the SST anomaly, with greater leaf flushing occurring during the period of the annual butterfly migration during El Niño events. Combining these and our previously published results for the migratory butterfly Aphrissa statira and its host lianas, we conclude that dry season rainfall and photosynthetically active radiation can serve as primary drivers of larval food production and insect population outbreaks in Neotropical wet forests, with drier years resulting in enhanced plant productivity and herbivore abundance. If climate change brings about a more El Niño-like mean state, tropical forest productivity and abundances of associated herbivores will increase. Insect populations should also closely track changes in both frequency and amplitude of the El Niño Southern Oscillation.

Last Modified: 7/28/2014