Hormones Regulate Behavior in Response to Stress

Biological Strategy

Insects

Andy Carstens

Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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A distinct set of hormones alter insect behavior by changing metabolic function during times of stress.

Introduction

Perhaps because we don’t always notice them, it can be easy to forget the value bugs bring. Many birds, mammals, fish, and reptiles depend on insects for food, making them an integral part of a vast food chain. Insects pollinate flowering plants and crops, providing food indirectly to humans and other large animals. Many insects also help clean our environment, feeding on waste like dung and dead plants and animals.

Although the sight of certain insects may cause stress in certain people, insects themselves experience stress from many causes as well. Extreme weather, famine, pesticides, and even crowding can cause stress in insects. Similar to humans and other animals, hormones regulate how insects respond to stress.

The Strategy

Humans have a “fight or flight” mechanism driven primarily by , a classified as a biogenic . Insects also produce biogenic amine hormones as their first line of defense to an immediate threat. In humans, the fight or flight response diverts oxygen and blood from less urgent functions to muscles, priming them for action. In insects, these hormones alter metabolism to supply muscles with immediate energy, also mobilizing them to battle or escape from a predator.

Humans and other vertebrates use glucocorticoid hormones to weather longer-lasting stressors. Insects use a related class of hormones, called ecdysiotropins, but other hormones also help them survive extreme conditions. In most cases, these hormones work together to shift metabolism and sustain energy demands. Adipokinetic hormone, for example, provides added energy to wing muscles during stress flight.

Image: Yuichi Kageyama / https://unsplash.com/photos/4ByFHyNdoD4 / Public Domain - No restrictions

In some species of the Lepidoptera order, stress can initiate the onset of larval diapause, which is a state of suspended development.

Australasian figbird trying to catch a beetle in mid-air

Image: Mdk572 / https://commons.wikimedia.org/w/index.php?curid=12584969 / CC BY SA - Creative Commons Attribution + ShareAlike

This beetle’s “fight or flight” hormones are likely surging as this Australasian figbird chases it with hopes of making it a tasty snack.

Image: Nonauk / CC BY NC ND - Creative Commons Attribution + Noncommercial + NoDerivatives

Silkworms provided the first insights into how insects synthesize ecdysiotropin hormones.

However, ecdysiotropins and other hormones that influence stress also affect normal insect growth. Adding to the complexity, growing insects undergo metamorphosis—molting or transforming from larva to pupa or from nymph to adult, depending on the type of insect. It’s not yet well understood how stress affects insects in different life stages, and scientists have observed a range of responses. For example, the same injury caused premature molting in younger caterpillars but delayed molting in older ones. Also, some stressors slow growth, while others accelerate it.

We need bugs, but multiple lines of evidence point to insect populations and diversity plummeting all over.

The Potential

Even though insects have a different stress response than humans and other animals, studying it is important because of the role insects play in ecosystems around the world. We depend on the contributions they make, and multiple lines of evidence point to insect populations and diversity plummeting all over. In areas where species are threatened, perhaps we can develop methods that adjust their metabolisms to help them thrive in the face of global warming and other human-caused environmental stressors. We may even abandon the use of toxic pesticides, and instead develop land treatments that influence hormones and behavior in more life-friendly ways.

“Fight or Flight” and “Emergency State” Manage Stress

Vertebrates (Mammals, Fish, Birds, Reptiles)

Two classes of hormones drive different responses to help vertebrates survive short- and long-term stressors.

Biological Strategy

Stress Response Suppressed to Prioritize Reproduction

Birds

In the face of environmental stress, birds with fewer chances to breed suppress their stress response, keeping their focus on reproduction instead of survival.

Last Updated February 14, 2021

References

“The neurohormones are the master regulators of all life processes in insects and they create a strategy of stress protecting events. Neurohormones are synthesized mainly in insect brain neurosecretory neurons. Various stressors of different intensity cause specific changes which influence on neurosecretory neurons activity and synthesis of neurohormones (biogene amines, ecdysiotropins, ecdysiostatins, allatoregulatory neurohormones, adipokinetic neurohormones, etc.).”

Journal article

Neurohormones In Insect Stress: A Review

Archives of Biological Sciences | Vesna Perić-Mataruga, Vera Nenadović, and Jelisaveta Ivanović

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