Chemicals Control Aphid Activity

Biological Strategy

Ants

Elyse DeFranco

Biological Control of Populations, Pests, Diseases

An ecosystem must prevent overpopulation of any given species within it, as well as the spread of pests and diseases, to allow organisms to survive without threatening extermination of other organisms or ecosystems. To control pests and diseases, living systems use such strategies as developing antibodies and killing or repelling pests or disease-causing organisms. Ecosystems have checks and balances to maintain populations, pests, and diseases. For example, in a lake, a balance of predators, prey, and nutrients is crucial for proper functioning of the ecosystem. Predatory fish keep down the numbers of smaller prey fish, which in turn keep populations of algae-eating zooplankton in check. When the levels of any of these organisms change, the change can disrupt the health of the entire ecosystem.

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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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Ants use chemical signals to control aphid dispersal and collect their honeydew for food.

Introduction

Species often find innovative ways to make use of others beyond a simple predator-prey relationship, intertwining their existence in a way that can bring benefits to one or both species. Ants are a great example of this, having developed ways of manipulating other insects for their own gain, including the aphids that for humans are persistent garden pests.

By understanding these species pairings, we can sometimes use them for our own benefit, such as targeting a pest species with a parasite or other biological control.

The Strategy

As social insects, ants live in large, structured colonies with designated roles for each individual. The queen ant lives her entire life under the protection of the rest of the colony, growing and producing eggs as the sole reproductive individual. Other female ants act as foragers and scouts, searching out sources of food to return to the colony.

But foraging for food takes a lot of energy, so some ants have found ways to make other species produce food for them. The black garden ant (Lasius niger, found in kitchens and backyards around the world) has developed a clever way of using aphids to produce food. The black bean aphid, Aphis fabae, feeds on the phloem sap of plants and produces a sweet, sugary fluid called honeydew as a byproduct. This honeydew is more nutritious and attractive to ants than the aphids themselves, so rather than prey upon the aphids, the ants “milk” them by using touch to stimulate the release of honeydew. They’ll even corral the aphids in order to collect the honeydew efficiently, similar to the way humans manage dairy cows.

Honeydew is more nutritious and attractive to ants than the aphids themselves, so rather than prey upon the aphids, the ants “milk” them by using touch to stimulate the release of honeydew.

The ants control the movement of the aphids in a number of ways. In addition to physically removing their wings to prevent them from flying to new host plants, the ants produce a chemical that has a tranquilizing effect on the aphids, preventing them from dispersing without reducing their honeydew production.

Chemicals that convey signals for other organisms are known as semiochemicals, and they can be used to communicate with individuals of the same species or that of other species. In fact, it’s not just animals that can produce these chemicals––many studies have shown that when under attack by aphids or other insect pests, plants often respond by emitting semiochemicals, which attract aphid predators such as ladybugs. The chemicals also work as airborne signals that can trigger surrounding plants to produce their own defenses in preparation of aphid infestation.

One of the chemicals produced by plants as a response to aphid presence is dendrolasin, which is the same chemical used by the ants to tranquilize aphids and prevent them from dispersing. Like good shepherds, the ants are quick to defend the aphids when predators show up to attack. In fact, the ants tend their colonies so effectively that they enable the aphids to continue to thrive under conditions that would normally cause them to disperse to other plants. And when a plant’s resources are exhausted, ants will carry their aphid colony to optimal plants nearby.

The Potential

For humans, aphids don’t yield sweet nectar, they colonize and feed on many important crops, resulting in significant losses in yield. They also spread plant diseases as they exhaust the resources on one plant and move on to the next. Our knowledge of the complex relationships between ants and aphids can help us to think beyond broadscale use of pesticides, and to protect crops in more natural and sustainable ways. How sweet would that be?

Last Updated January 22, 2021

References

“Aphid walking speed was significantly reduced in the presence of ant semiochemicals… [and] ant presence is not required to obtain a tranquilizing effect upon aphids. Instead, semiochemical cues are necessary and sufficient… through limiting individual movement, ant semiochemicals may interfere with both local (apterous) and long-distance (alate) dispersal of aphids… Chemicals, such as dendrolasin, that are produced by ant mandibular glands can limit alate development.” (Oliver et al., 2007:3129)

“To summarize, we show how the dispersal of a pest organism can be affected by interspecific chemical communication with a mutualist. The outbreak of such pests is likely to be highly dependent on these interspecific interactions.” (Oliver et al., 2007:3130)

Journal article

Ant semiochemicals limit apterous aphid dispersal

Proceedings of the Royal Society, Biological Sciences | October 10, 2007 | Thomas H. Oliver, Alla Mashanova, Simon R. Leather, James M. Cook and Vincent A. A. Jansen

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Reference

“In recent decades, many studies have shown that plants produce volatile organic compounds (VOCs) in response to attacks by herbivorous insects and that these induced VOC emissions can confer protection to the plant by acting as signaling compounds at different trophic levels. As such, herbivore-induced VOC emissions have been shown to directly deter further attack by herbivorous insects to attract predators or parasitoids of the feeding insect. Furthermore, VOCs released from the attacked plant parts can also serve as airborne phytohormones inducing defense responses in the non-attacked tissues of the same plant or of neighboring plants. Together, there is increasing evidence that induced VOC emissions are an important part of defense strategies against herbivorous insects that plants have evolved owing to their sessile nature.” (Staudt et al., 2010: 1320)

Journal article

Volatile organic compound emissions induced by the aphid Myzus persicae differ among resistant and susceptible peach cultivars and a wild relative

Tree Physiology | Michael Staudt, Benjamin Jackson, Hanana El-aouni, Bruno Buatois, Jean-Philippe Lacroze, Jean-Luc Poëssel, Marie-Helene Sauge, Ülo Niinemets

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