Ants

The main problem ants can cause is an increase in outbreaks of plant pests like mealybugs and scale insects. However, only some ants cause problems like this. A few ants, such as the green tree ant, can be beneficial for pest control. However, ants should never be introduced to new areas.

Common name

Many species. In the Pacific common pest ants in the Pacific include little fire ant, yellow crazy ant and African big-headed ant. Beneficial ants include the green tree ant. The little fire ant can be beneficial in some cases, but its harm outweighs its benefit.

Scientific name

Various species in the Family Formicidae

on this page: Life-cycle and identification : Symptoms : Impacts : Distribution : Prevention : Controlling ants : Information sources and further reading

Life-cycle and identification

Ants are insects that live in nests or colonies (made up of many nests). There are three types of ants in a colony: queens, workers and males.

Queens are responsible for all reproduction in the colony.

The males live only to mate with new queens and die shortly thereafter.

The workers, which are all female, are sterile and responsible for taking care of the brood (eggs, larvae and pupae), tending to the queen or queens, foraging for food and colony defense. Some species have different types of workers, such as the African big-headed ants.

Workers are the ants you are the most likely to see.

As all the reproduction in the colony is done by the queens, any management method has to kill the queen (usually invasive ants have many queens).

The three different kinds of ants: the large queen, the winged males and the many workers (© Meghan Cooling)

Reproduction

image 13_lifecycle of an ant

Life cycle of an ant. It should be noted that the wings of new queens fall off after the first few days or weeks of the queen’s life (Source: Ask a Biologist (© Arizona Board of Regents / ASU Ask A Biologist)

The life cycle of an ant is called complete metamorphosis. It is the same kind of life cycle butterflies have.

However, some aspects of the life cycle are unique to ants, which influences the methods needed to kill an entire colony.

Eggs are laid by the queen, and then hatch into larvae after 6-32 days, depending on the ant species and temperature.

Larvae grow and are fed and cared for by the workers.

In 12-32 days, the larvae then become pupae, and the workers stop feeding them.

Pupae are covered by a white or brownish cocoon.

When they are fully developed (9-30 days) adult ants emerge from the pupae.

Workers are produced all year round in warmer regions, while reproductives (queens and males) are produced once a year, often at the beginning of the rainy season.

The Pacific Invasive Ant Toolkit has information on how to identify the worst invasive and pest ants.

Symptoms

Ants can be seen farming, protecting or tending (caring for) pests such as mealybugs and scale insects.This causes an increase in the numbers of these insects and they become pests.

They can also be seen making trails back to their nests. When they are feeding on coconut nectar or scale / mealybug they can be seen trailing down the palm.

Impacts

Typically ants have an indirect impact on coconut by farming scale and mealybugs, which stress crops and encourage plant diseases, reducing yields for farmers. However, they can also make working in plantations difficult.

For example, ants like the little fire ants (Wasmannia auropunctata) cause hardship for people living and farming in invaded areas.

Harvesting is also difficult due to the ant’s painful sting.

In New Caledonia, the Galápagos Islands and French Polynesia, coffee and cocoa farms where the crops must be harvested by hand, have been completely abandoned to the little fire ant.

The extremely painful sting makes harvesting difficult. Some farmers have found it unprofitable to pay workers the increased wages they require to work under such conditions.

Little fire ants are known to blind livestock and pets, though wild animals are affected as well.

Little fire ants support sap-sucking insects which encourage plant diseases like the fungus shown here growing on coffee (© Cas Vanderwoude)

The green tree ant and the little fire ant have been shown to drive out pests, such as the nutfall bug, from coconut palms in some cases. Their effects on other pests has not been studied. So while, a beneficial impact is possible, introducing any ant species to a new area is not recommended.

Distribution

Ants are found on all continents except Antarctica. The Pacific Invasive Ant Toolkit has information on the distributions of the worst invasive and pest ants.

Prevention

Ants are very difficult to control. Good biosecurity is essential to prevent new ants arriving in a country or a new area. See the Pacific Invasive Ant Toolkit for information on biosecurity actions to prevent the worst invasive and pest ants.

For general information on preventing pests and diseases of coconut, see the Prevention section.

Controlling ants

We strongly recommend an integrated pest management (IPM) approach to the control of all insects, where possible. This is a combination of methods (pesticides, physical controls such as site hygiene and biological controls) to minimise the use of pesticides and minimise the cost of control. Insecticides are not effective at controlling CRB.

Integrated Pest Management (IPM)

The goal of IPM is to keep pest populations to a level below which they cause economic harm. IPM involves using multiple control options together for the economic control of pests (i.e. cultural, natural and chemical).

In an agricultural context the Food and Agriculture Organization defines IPM as "the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms".

Cultural : Natural : Chemical

As ants often cause problems when they are involved in mutualisms with pest insects, it is wise to combine ant control with control of these pests.

See the Pacific Invasive Ant Toolkit for detailed information on controlling ants.

NOTE: Nest destruction is not advised against the green tree ant, Oecophylla smargadina, as its effects are mostly beneficial.

Natural

There are no biological controls of ants as they have no significant predators (apart from anteaters).

Cultural

The number one thing you can do to lessen ant problems is to remove resources e.g. nesting materials, food scraps, and treat the plant pests that are helpful to ants.

Rubbish piles are a great source of food and nesting locations for invasive ants.

Keep areas around coconut palms free of vegetation and debris that ants can nest in.

Hibiscus is a major attraction for ants (and as a host plant to insects that carry coconut disease). Hibiscus fences should be well away from coconut palms.

Ant nests can be treated by salt water dousing (if near the sea) involves looking for the ant nest and destroying it (i.e. targeted treatment of nests with salt water dousing).

The idea is to follow the worker ants back to the nest entrance and flood the nest with salt water.

Rubbish piles provide a fantastic source of food and nesting locations for invasive ants (© Monica Gruber, Pacific Biosecurity)

This forces the queens out of the nest. It is important to to stay and wait for the queens to leave and kill them directly. Queens are very good at escaping and hiding so you need to look carefully. The nest and surrounding area needs to be checked over the following few days and re-treated if necessary.

Note that if the nest isn't effectively destroyed remaining queens and workers can leave and start a new colony.

It is important to note that all control methods require regular site visits and repeat of the control method. This is because the presence of invasive ants throughout the landscape means that sites left untreated will be recolonized.

Dousing with salt water is a very labour intensive method, but an option if there aren't any others.

Hot water can also be used to kill entire colonies of ants if a large enough volume of hot water is applied directly to the nest (using a large kettle for example). Water temperature should be above 65°C (and ideally above 82°C) to be lethal to the ants.

Precautions must be taken with hot water methods to avoid burns. This treatment must never be undertaken around children.

The volume of water applied will depend upon the size of the nest. For very small colonies 4 L of water may be enough. For larger colonies as much as 75 L of hot water may be necessary to reach the below-ground nest structure and kill all of the ants. Be sure to watch out for the queen (s) leaving the nest. If you fail to kill the queen, she will simply make another nest nearby.

For locating the nests of invasive ant species whose nests are not so obvious, follow workers back to their nest.

Chemical

Pesticide control of ants relies on workers picking up the pesticide loaded bait and bringing it back to the colony to feed the queens and larvae. Pupae are not fed as they are in a cocoon.

As the pupae aren't fed the pesticide, when they come out of the pupal stage they can survive even though the rest of the colony may have been killed. Without their queens eventually they too will die.

But queen and male pupae don't get fed the pesticide. When emerge from the pupal stage they can potentially start the colony all over again.

This is why timing of insecticide treatment is important - ants must be at the right stage of their life cycle.

Yellow crazy ant workers tending to larvae and pupae (© Meghan Cooling)

Information sources and further reading

ASU School of Life Sciences. 2018. Face to Face with Ants. [ONLINE]

PIAT. 2018. The Pacific Invasive Ant Toolkit. [ONLINE]

content reviewed by Bob Macfarlane, Solomon Islands, September 2018