Insect populations are "dramatically" declining around the world as scientists sound alarm

Insects play a crucial role in food chains and pollination. Over the last 20 years, their populations have dramatically declined due to rapid climate change.

In a recent study, scientists have gained new insights into how certain fly species adapt to temperature shifts.

Researchers at Northwestern University studied two species from different climates: one from high-altitude forests in Northern California and the other from the hot deserts of the Southwest.

The findings reveal key differences in how these flies sense and respond to heat. The study suggests that changes in brain wiring and heat sensitivity influence whether a fly prefers warm or cool conditions.

This research may help predict how climate change will impact insect distribution and behavior. Tiny cold-blooded animals like flies rely on their environment to regulate body temperature.

Their responses to temperature shifts offer valuable insights into the broader effects of climate change.

How flies adapt to temperature

The scientists found that flies from cool forests avoid heat due to their antennae’s molecular heat receptors.

In contrast, desert flies are drawn to warmth, which is linked to changes in their brain wiring. These adaptations may have evolved over millions of years as each species adjusted to its environment.

The research sheds light on how animals develop preferences for specific temperature conditions. Understanding these adaptations can help predict future insect behavior in a rapidly changing world.

Limited data on insects and climate change

“Insects are especially threatened by climate change,” said Northwestern neurobiologist Marco Gallio.

“Behavior is the first interface between an animal and its environment. Even before the struggle to survive or perish, animals can respond to climate change by migration and by changing their distribution.”

“We are already seeing insect populations declining in many regions, and even insect vectors of disease like the Zika virus and malaria spreading into new areas.”

Gallio, a professor in the neurobiology department and the Soretta and Henry Shapiro Research Professor in Molecular Biology at the Weinberg College of Arts and Sciences, studies fruit flies and their sensory systems.

Professor Gallio noted that limited data exist on insects and temperature because “not enough people care about the insects.” However, the available figures show a drastic decline over the past 20 to 50 years.

Insects pollinate 70% of crops and form the base of most terrestrial food chains. Their disappearance could trigger catastrophic ecosystem damage and directly affect human well-being.

Temperature sensitivity in flies

Professor Gallio’s lab has long focused on how small insects respond to different temperatures.

“The common fruit fly is an especially powerful animal to study how the external world is represented and processed within the brain,” Gallio said.

Years of genetic and neuroscience research have created a detailed map of the fly brain, more complete than that of any other animal.

Scientists wondered how brain circuits differed between species that lived in distinct thermal environments.

Using tools like CRISPR, they studied genetic and neural mechanisms that shape temperature preferences.

PhD student Matthew Capek, lead author of the study, explained that flies from different climates detect heat at different activation points.

This discovery partially explained the forest flies’ preference for cooler temperatures. However, it did not fully clarify the desert flies’ attraction to heat.

Seeking the right insect temperature

“The desert fly seemed actively attracted to warmer temperatures – around 90 degrees Fahrenheit compared to the forest fly’s sweet spot just below 70 degrees,” Capek said.

“In fact, the activation threshold of the antenna heat sensors corresponded to their favorite temperature range, which they will seek, rather than to a temperature they should avoid.”

Instead of avoiding high temperatures, desert flies interpret warmth as something positive. Their brain circuits appear wired to approach heat rather than flee from it.

Why desert flies seek heat

Gallio initially found this puzzling. If deserts are already hot, why would flies seek out warmth? A research trip to the Anza Borrego desert of Southern California provided the answer.

“Deserts in this region are very hot during the day, but temperatures can drop extremely rapidly when the sun goes down, and night can be downright freezing,” said Alessia Para, a research associate professor of neurobiology and key author of the study.

“Flies in this climate may need to constantly attend to the rapidly changing temperature and always seek the ideal range, finding shady spots during the day and hiding in cacti for warmth at night.”

Flies from milder environments may only react to extreme temperature shifts. In contrast, desert flies must continuously monitor temperature changes to survive.

Insects, climate, and temperature

Tracking the right temperature at all times is energy-intensive. For desert flies, however, it is a necessary survival strategy.

Professor Gallio sees their behavior as part of a larger puzzle about how animals adapt to different climates.

“This comparative work is useful in a couple of different ways,” Gallio said.

“When an animal is born, the brain is already programmed to know if many of the things it will encounter are bad or good for it, and we do not understand how that programming works.

“These fly species represent a natural experiment because a stimulus that is good for one species is bad for the other, and we can study the differences that make it so.

“We also want to learn more about how animals have been able to adapt to different temperatures during evolution, so that we may be able to better understand and even predict how they react to ongoing climate change.

“Of course, we care about the insects, and we hope that what we learn may help us appreciate and protect them better.”

The study is published in the journal Nature.

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