Enlarge/ Ants from the species Pheidole megacephala tending aphids. They protect the tiny insects from predators and milk them for a sugary fluid called honeydew.
One of the worst effects of ant infestation doesn’t happen inside your house or on your picnic blanket. It takes place in farms and gardens, where many species of ants tend to herds of aphids. These tiny insects are a bane to plants—aphids weaken plants by feeding on their sap, and they sometimes transmit deadly viruses while eating. This has earned aphids the nickname “plant lice.” But for ants, aphids are more like cows. They secrete a sugary fluid called honeydew that ants love to eat.
- Aphid ranchers on the mugwort frontier
- Long-term planning
- Ants farm aphids in a symbiotic relationship
- Aphids manipulate their food
- Biology Teaching Resources. Aphids
- How Do Aphids Help Ants: Controlling Aphids And Ants On Plants
- Are Aphids Farmed by Ants?
- How Do Aphids Help Ants?
- Aphids and Ant Control
Aphid ranchers on the mugwort frontier
Just as humans have transformed millions of acres of open land into ranches for cattle, ants can easily transform fields into aphid ranches. A new study by a group of environmental scientists in Japan reveals that ant cultivation of aphids isn’t a haphazard process, either. Researchers in Science Advances describe an experiment where they discovered that ants in a Hokkaido field are often the only factor that prevents aphid colonies from going extinct. In addition, the ants prefer aphid colonies with a nice balance of green and red aphids, and they select aphids to exhibit these colors.
Even though many ant species tend aphids and similar sap-eating insects, the researchers focused exclusively on ants from the species L. japanocus. These ants tend colonies of the species M. yomogicola, a kind of aphid that feeds on the mugwort plant. The researchers identified three groups of eight aphid colonies for observation. They left one group alone to be tended by ants, while another group was isolated from their ant benefactors by painting the base of their mugwort homes with a sticky substance called Tanglefoot that prevents ants from climbing the stalks to their herds. The third group was a control, tended by ants, but exposed to a minimal amount of Tanglefoot. This was just to measure the effect of Tanglefoot on aphids (it was negligible).
The results were stark. All but one of the aphid colonies that were not tended by ants went extinct. Of the surviving aphid colony, only one aphid remained. Without ants to protect them, the aphids were eaten by predators like ladybug larvae and parasitoid wasps. Apparently, ants remove these predators from their herds when they come to milk the aphids for honeydew. The ants win, the aphids win, but the mugwort suffers. A version of this scenario plays out all over the world, where ant invasions often mean aphid invasions, too.
Here you can see some of the ants and mugwort aphids that the researchers studied. The “red” aphids appear brown and orange, while the “green” ones appear green and black. Watanabe et. al. What’s especially intriguing about this recent experiment, however, is that the researchers discovered that ants have a distinct preference for aphids whose colonies exhibit a balance of green and red aphids. The optimal ratio, in fact, seems to be about 65 percent green to 35 percent red. There are only a few reasons why animals exhibit this kind of polymorphism, or persistent maintenance of two or more distinct body types within the same species. Sometimes polymorphism is a way for an animal to adapt to different conditions or environments, or there’s a strong advantage to having a few members of the group exhibit an unusual color or body type. Neither of these explanations accounts for the color polymorphism among L. japanocus. The mugwort aphids are all in the same environment, and both colors are subject to the same levels of predation.
Ants simply seem to prefer tending herds with a relatively balanced number of greens and reds. Because aphid colonies tended by ants have a much higher survival rate than ones without ants, it seems likely that selection pressure for this color polymorphism comes directly from ant shepherds.
The question is why do ants like this color balance? One possibility is that red and green aphids have slightly different effects on the mugwort plants where they feed. Though green aphids produce more honeydew, reds seem to prevent the mugwort from flowering. Given that aphid colonies on a flowering mugwort go extinct, ants looking to maintain a herd for more than a year might see an advantage to keeping reds around to guarantee a long-term food supply from their green sisters.
It appears that ants aren’t just opportunistically squeezing honeydew out of any old aphid colony. They are deliberately maintaining aphid herds, possibly for many seasons, by carefully selecting for a ratio of red and green insects. This kind of long-term planning guarantees herd longevity and, ultimately, a good food supply for the ant colony. It’s just another way that ants are uncannily like humans, both in their quest to convert land into farms and their undying love of sugary fluid from dubious sources.
Science Advances, 2016. DOI: 10.1126/sciadv.1600606 (About DOIs)
Ants farm aphids in a symbiotic relationship
© Ants: Natures secret power
Many ants have developed a variety of symbiotic relationships with other invertebrates and plants, sometimes to mutual benefit, sometimes not.
One of the most common is the herding or farming of sap feeding insects ‘homopterans’ such as aphids, scale bugs and mealy bugs.
These insects obtain their own food from plants and pass some of it on to the ants as highly nutritious nectar or honey dew. In return, the ants tenderly look after and protect them from predators.
By stroking the back of some aphids with their antennae, the ants can induce a honeydew droplet.
The ants may move the insects to areas on the plants with the best sap.
When it rains they may move them to sheltered places, even sometimes into their own nests.
Although this process seems very pleasant for both parties, recent studies show that ants sometimes clip the wings off aphids to stop them flying away. They also use chemicals found on their feet to drug them, preventing their wings from developing. It appears that the ants are very much in charge. (Telegraph)
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- © Bastiaan Schuit
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The Lasius Family and Aphids
The yellow meadow ant (Lasius flavus) has an intimate relationship with aphids. The species seldom travels above the surface, which can be concluded by looking at their small eyes, in comparison to other Lasius-species. They do not need to see very much, since they spend most of their lives in darkness. The flavus ants therefore make use of root louses. A sort of aphid living in the ground on the plant roots.
Both the black garden ant and the yellow meadow ant can bring home aphid eggs or herds of aphids to the colony. This is to keep them there, safe, during the winter season. In spring, they are placed on suitable pastures and are moved around until the ants have located the perfect spots (3). The species of Lasius neoniger treats aphids as any other member of the colony, and their eggs are cared for the same way as the ant eggs. (4)
Ants do not only cooperate with other insects. They can also form a symbiosis with different plants. The Indian plant of Nepenthes bicalcarata is a plant that feeds on insects falling down into its mouth. In other words: an insectivorous plant. In spite of this, whole colonies of ants can live in its cavities. How?
Just like with aphids, ants provide the plant with protection – mostly from herbivores. In exchange for this, the ants are provided with a safe place to live (with the exception of the risk of being eaten in their home), and with some of the plant’s prey. There are hundreds of interesting ant-plant symbiosis described from 150 years of research (5). Ants has become the perfect lodgers of the plant-houses. They protect it from enemies, distributes its seeds and cares for its roots in the form of dirt and nutrition. In exchange, plants can produce nectar of different kind, perfect for the ants.
It is general knowledge in the myrmecology department that ants can protect plants from other insects and pests. But what is not really confirmed is that ants can protect plants from animals as big as cows, horses of humans. This has been observed, but there is not enough scientifically data to prove it – yet. An example of this is a worker of the species of Pseudomyrmex (America) that can smell large mammals and, with the rest of the workers, runs out of the plant to defend it. When compared to a non-protected plant the result is thrilling. The plants with ant inhabitants get on much better than the ones without. The latter must fight pests, insects and mammals all on their own (6). This proves that a symbiosis with ants might be something to think about.
Aphids manipulate their food
Aphid infestation of the stem close to the bud of a tansy. Credit: Bielefeld University/Jana Stallmann
How do aphids reproduce on plants so successfully? This is among the questions that Professor Dr. Caroline Müller and her research team are addressing at Bielefeld University’s Faculty of Biology. They have discovered that aphids are able to influence the quality of their food, and that this may enable them to construct a niche on their own host plants. Müller’s research team is located in the Transregio Collaborative Research Centre NC3 that is studying animals and their individual niches. They have published their findings in the journal New Phytologist.
There are hundreds of aphid species. They all feed on plant sap, known as phloem sap. The nutritional value of the phloem sap is determined by the sugar concentration and the concentration and composition of amino acids. Previously, it was not known how the quality of plant sap changes in different plant parts after aphid infestation, how this change in quality influences the development of aphids, and how, in turn, the aphids can change the composition of the plant sap.
Müller and her team are the first to confirm that aphid infestation actually does change the composition of the plant sap depending on which aphid species is infesting which specific part of the plant. For example, infestation of the stem close to the bud with a certain aphid species changes the composition of sugar and organic acids in the sap. In contrast, infestation of the old leaves with another aphid species increases the concentration of amino acids. And a further phenomenon can also be ascertained: “We were able to observe that the aphid species that developed best on the stem close to the bud and the other species that proliferated best on the old leaves each specifically increased the quality of the plant sap of the corresponding plant part,” says Ruth Jakobs, a research assistant at the Faculty of Biology. Hence, aphids construct their own niche in such a way that they are able to profit from it. “We can assume that aphids behave in a similar way to, for example, beavers that settle in the dams they have constructed themselves,” says Müller.
The biologists gained their findings by placing aphids on different parts of common tansy plants—the stem close to the bud, a young leaf, and an old leaf—and determining the growth of the populations of these insects at these locations. In addition, the biologists collected the plant sap and analysed its chemical composition.
Protein restricts sap uptake by aphids More information: Ruth Jakobs et al, Aphid infestation leads to plant part-specific changes in phloem sap chemistry, which may indicate niche construction, New Phytologist (2018). DOI: 10.1111/nph.15335 Journal information: New Phytologist Provided by Bielefeld University Citation: Aphids manipulate their food (2018, August 1) retrieved 1 February 2020 from https://phys.org/news/2018-08-aphids-food.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
Biology Teaching Resources. Aphids
For illustrations to accompany this article see Insect Life-Cycles
The aphids are probably best known as “greenfly” on roses or “blackfly” on broad beans. They belong to a group of insects known as “bugs” or Hemiptera, the mouth parts of which are modified to form piercing and sucking tubes, the insects obtaining their food by sucking plant juices or the blood of other animals. Water boatmen, for example, are Hemipterans which prey on other pond creatures; the frog-hoppers and “cuckoo-spit” insects draw fluids from plants. This group of insects has an incomplete metamorphosis, there being no pupal stage but a series of moults in which the nymph gradually becomes a mature adult.
There are over 400 species and varieties of aphids but the account given below applies in general to those commonly encountered as garden and orchard pests.
Life history. In October the females lay eggs usually on the stems of trees or shrubs. The eggs are black, with thick shells and can withstand extremes of temperature. It is in the egg form only that aphids pass the winter. In March the eggs hatch out into wingless female nymphs which are similar to the adults, with three pairs of legs, compound eyes, antennae, etc. There is no larval or pupal stage comparable to those of the butterfly, but with successive moults and continuous growth the nymphs become mature females. No males are hatched at all.
The female nymphs feed on the shoots and leaves of the tree on which they hatch, at the time when the buds are sprouting. After a series of ecdyses (moults) they become mature and give birth to daughter aphids without any fertilization. This kind of reproduction is called parthenogenesis. The daughters, moreover, are not produced from eggs but are born alive as nymphs though they are surrounded at first by a transparent capsule like an egg membrane.
The daughters grow quickly and themselves have offspring by parthenogenesis. Some of these develop wings which grow larger at each ecdysis. These winged daughters fly off to an herbaceous plant such as a rose tree or bean plant. The winged forms have two pairs of wings of which the hind pair are quite small. Both pairs are transparent with few veins. The aphids are not strong fliers but tend to be carried by chance air currents rather than make direct flights. Spruce aphids were once found in Spitsbergen, and are thought to have been carried in the upper air some 800 miles across the sea from Russia where the nearest spruce trees grow.
When the winged generation reach the new food plant they give birth to wingless daughters parthenogenetically. In warm weather these may mature in 8 to 10 days and begin to reproduce in the same way by bearing winged daughters which fly off and infest new plants. This process of parthenogenesis goes on all through the summer months, winged and wingless generations more or less alternating. Enormous numbers of aphids are produced in this way, though a great many are killed by birds, ladybirds and their larvae, lace-wing larvae, and cold weather.
In October the first males appear. They have wings, and fly to a tree. Winged females fly to the same tree and there give birth to wingless daughters. The males mate with these when mature, and the wingless females subsequently lay eggs on the twigs of the tree. The eggs remain dormant until the following spring when the tree buds begin to sprout.
Feeding habits. Nymphs and adults feed in the same way. Their mouth parts consist of a slender tube with two sharp stylets running down each side. All these are enclosed in the sheath-like labium and are held horizontally below the thorax when not in use. During feeding the labium is bent and shortened as the stylets and central tube are pushed through the epidermis of the leaf or stem until they reach the sieve tubes of the phloem in a vascular bundle. Saliva is injected through the puncture to begin the digestion of the sap and cytoplasm, and the fluids are then pumped up by muscular movements of the gullet into the alimentary canal. The fluid pressure existing in most plant cells probably assists the flow of liquid through the aphid’s mouth parts. Most aphids seem to take in from the plant sap more sugar than they can assimilate, so that their faeces consist of a sweet syrup, honey dew, that is passed out of the anus. Some species of ant like to feed on this exudation and may be seen clambering over the colonies of aphids on nettles and other plants to collect it. Other species of ants ‘farm’ aphids by keeping them in the nest below ground where they suck fluids from roots, the ants then collecting the honey dew as it is egested.
Damage and control. A large number of aphids on the growing shoots of a plant can cause damage, partly by the excessive removal of food that would otherwise pass to the growing leaves, partly by the digestive action of the saliva injected and also by introducing virus diseases from one plant to another, particularly in the potato, sugar beet and sugar cane. Young leaves attacked by aphids usually curl up and wither and the growth of the entire shoot may be arrested.
Aphids can be destroyed by spraying them with solutions or suspensions containing insecticides which kill them on contact. Covering the leaves with poisons is useless because the aphid draws its food from below the surface. For this reason systemic insecticides are often used. These are absorbed into the plant tissues so that the aphids are poisoned when they ingest the plant juices. Once the leaves have curled up under a heavy aphid attack it is difficult to reach the insects with sprays. A less direct method of control in winter is to spray the trees in the garden or orchard where the autumn eggs have been laid. Poisons dissolved in water run off the thick shell, so solvents such as paraffin, and liquids such as tar oil, are used, these penetrating the shell and destroying the egg. This must be done before the foliage develops, otherwise the sprays will damage the leaves.
Larval and adult ladybirds eat a great many aphids, and an ichneumon parasite causes many deaths by laying its eggs in the bodies of the aphids. These predators, parasites and spells of cold weather help keep down the numbers of aphids.
For illustrations to accompany this article see Insect Life-Cycles
How Do Aphids Help Ants: Controlling Aphids And Ants On Plants
Who would consider ants farmers? Plant pests and picnic nuisances, yes, but farmer is not a vocation naturally assigned to these tiny insects. However, it is a true circumstance in which they herd and care for aphids in order to keep a much loved food in constant supply. Aphids and ants on plants are as interdependent as peanut butter and jelly.
Are Aphids Farmed by Ants?
Aphids are sucking insects that are common on both outdoor and indoor plants. They feed on the sap of plants and secrete a substance called honeydew. This sticky resin is a favorite food of ants, who actually “milk” the aphids for it by stroking their abdomen. The relationship between aphids and ants is symbiotic in that both receive some benefit from the arrangement.
The unique relationship between these two organisms provides protection for the aphids and food for the ants. Ants protect the aphids from predators, such as lacewings and ladybugs.
They have also recently been found to protect the aphids from a fungal outbreak that causes death, by removing the bodies of the infected aphids.
Anytime you see a large number of ants on a tree or plant, it is likely you have a large infestation of aphids. Not all species of ant find this arrangement beneficial, but many of the more common species do indeed farm aphids in this way.
How Do Aphids Help Ants?
How do aphids help ants? Aphids feed the ants and docilely allow themselves to be moved if the ants require them to relocate. It is a fascinating arrangement where aphids and ants on plants live in close cooperative proximity.
Farmed aphids supposedly produce larger drops of honeydew and more offspring. The sweet sticky stuff is a favorite food for ants, who also take it back to feed larvae. Plants where there are aphids farmed by ants may appear to be overrun by insects. This is where aphids and ant control take center stage.
Aphids and Ant Control
Managing ants is one way of controlling the aphid population. Ant bait stations are effective because the ants take the bait and bring it back to the main colony. This destroys more of the insects at one time. With less ants to defend them, aphid numbers will drop.
A non-toxic method is to simply wrap the plant or tree with sticky tape or netting. This catches the ants and prevents them from tending to the aphids. In turn, the aphids are exposed to predators and their numbers will dwindle.
Conversely, you can focus your attention on the aphid population. Without aphids, the ants will be forced to move on for food. Horticultural soap sprays or neem oil work well for aphid control.