On December 10, 2019, Drs. Dan Janzen and Winnie Hallwachs spoke at the Entomological Society of America's Program Symposium on Insect Decline in the Anthropocene. In the talk, "Where Might Be Many Tropical Insects," Dan spoke of his very real experience of seeing the abundance and diversity of tropical insects decline since he first went to Costa Rica in 1963. The cause, he says, is not agriculture, noting that there have been 400 years of agriculture in Costa Rica. The main problem, according to Dan and Winnie, is climate change. In 1963, the dry season lasted four months in Guanacaste. Today, it is six months long. And the start and end points of the dry season, once like clockwork, are increasingly erratic. The tropics, they say, are much more sensitive to a given amount of temperature change than places that are used to wide fluctuations in temperature. "The house is burning," say Dan and Winnie. "We do not need a thermometer. We need a fire hose." Their paper of the same name can be found in the journal Biological Conservation here.
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