Unattractive Lights : For the modern moth - flames just aren't the draw they used to be.

It used to be that you could put a black light at the edge of a cornfield at night and expect a bountiful harvest of moths the next morning.

For entomologists, such light traps have provided an invaluable record of moth numbers. But in recent decades, light traps have shown dwindling catches of insects of all kinds. Some have interpreted these empty traps as evidence of their decline.

But there might be other factors at play. In a paper published last month in the Journal of Insect Conservation, researchers report that while some light traps are catching fewer corn earworm moths, a well-known agriculture pest, their yields in another kind of trap are as healthy as ever. The result suggests that something has changed in the moths' attraction to light.

Why the difference? It might be, as Charles Darwin once suggested, that evolution has removed moths with an attraction to light from the gene pool, so that today's corn earworm moth is no longer as drawn to light.

But another declaration for the decline in light trap-effectiveness might be that it's a consequence of the world surrounding those light traps growing much brighter. 

With streetlights and other sources lighting up the night, moths may not be noticing the light traps as much as they notice other glowing things.

The findings are a first step toward adjusting the way scientists approach insect monitoring, said Jolyon Troscianko, an ecologist at University of Exeter in England. 

'' This is very much a hot topic,'' he said. [ Veronique Greenwood ] 


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