Safeguard backyard ecosystems
Cornell University
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This ecological impact was demonstrated in
a new Cornell University study published in the Proceedings of the
Royal Society B: Biological Sciences.
The scientists placed more than 550
lifelike caterpillar replicas made of soft clay in a forest, setting to
ascertain how the mockups were attacked and hunted by predators compared to a
control group.
"We measured predation rates on the clay caterpillars -- which look like the real thing," said John Deitsch, who conducted the research as his undergraduate honors thesis in the nearly pitch-dark Hubbard Brook Experimental Forest, in the White Mountains of New Hampshire.
"Predators left marks on the clay. Predation rates on clay
caterpillars and the abundance of arthropod predators were significantly higher
on the artificial light at night treatment plots. This suggests an increase of
mortality pressure on caterpillars."
Deitsch and Sara Kaiser, research ecologist
and director of the Hubbard Brook Field Ornithology Program at the Cornell Lab
of Ornithology, co-authored the research, "Artificial Light at Night
Increases Top-Down Pressure on Caterpillars: Experimental Evidence From a
Light-Naive Forest."
The caterpillar models are made from green,
extruded clay to mimic the color and size of Noctuidae (owlet moths) and
Notodontidae (prominent moths) caterpillars. The soft clay easily allows for
imprints so that the scientists can determine if predators -- like arthropods,
insects, or birds -- landed on the model or tried to take a bite.
While effects of artificial light at night
have often been studied on adult insects (such as moths), the larvae
(caterpillars) have seen little research.
Of the 552 clay caterpillars deployed and
glued to leaves to look authentic, 521 models were recovered and 249 (47.8%)
showed predatory marks from arthropods, during the summer-long nighttime study.
Further, the research found that
caterpillar predation rates were 27% higher on experimental plots -- compared
to the control areas in the same forest -- that had 10 to 15 lux (about the
brightness of a streetlight), which is an illumination measurement for LED
lighting.
Given the global ubiquity of artificial
light at night, increased threat to caterpillars is yet another ecological
problem for lepidoptera, in addition to habitat loss, agricultural-chemical
pollutants, invasive species and climate change, according to the paper.
Caterpillars are the most vulnerable at
that larval stage. "They are eating leaves and growing in order to mature
to the next stage," said Kaiser.
"When you turn on a porch light, you
suddenly see a bunch of insects outside the door," Kaiser said. "But
when you draw in those arthropod predators by adding light, then what is the
impact on developing larvae? Top-down pressure -- the possibility of being
eaten by something."
Funding was provided by the Rochester Academy of Science, the Society for Integrative and Comparative Biology, the Cornell University College of Agriculture and Life Sciences, and an Experiential Learning Grant from the Cornell Lab of Ornithology Ivy Scholars Fund.
