Pest control - termites

Termites belong to the insect order Isoptera, meaning ‘equal wings’.

The digestive system of termites contains a variety of microorganisms to assist in the digestion of the plant fibre cellulose.

There are more than 350 species of termites in Australia, and few are considered pests. Only approximately 20 species cause damage to buildings. In Victoria, there are five species that cause damage to buildings and wooden structures.

Termites play important ecological roles by providing nest holes for lizards, birds and possums, breaking down organic matter, returning nutrients to soil and assisting with soil aeration.

Termites are often wrongly called ‘white ants’. This term should not be used because termites are neither white nor ants.

Termite colonies

Termites live and work together in nests or colonies. Members of the colony take different forms or ‘castes’. These include:

Alates

Alates, meaning ‘winged ones’, are the true adult termites.

They have eyes, wings, darker colouring and are fertile.

Their wings are equal size and shape and twice the length of their body. They shed after the colonising flight is made. Shed wings are a good indication of termite presence.

Reproductives

These are the sexual forms of the colony including future kings and queens of colonies yet to be established.

The reproductive’s live in a central chamber in the nest where a female, or ‘queen’, will lay many thousands of eggs each year over her life span of approximately 10 years. Male, or ‘kings’, are responsible for fertilising the queens. Multiple reproductives are commonly observed.

The young termites develop in the colony by shedding cuticles at the end of each growth stage, gradually changing until they reach the worker, soldier or adult (winged form). If queens die, some supplementary reproductives may carry on the colony as neotenics.

Reproductives are generally darker than workers and soldiers. They have functional eyes and their more robust skin (cuticle) is able to resist the outside environment. After flight, unlike other insects, the deciduous wings of termites are discarded and piles of shed wings are a good clue to termite infestations.

Soldiers

Soldiers have darker, larger heads than the other castes. They are blind, wingless, and have undeveloped reproductive organs.

Soldiers are tougher than the other castes and take longer to die from most toxins, exposure, or starvation. It is their role to defend the colony, if disturbed, while the damage is repaired by the workers.

Soldiers exist in different forms. Most species have soldiers, with well-developed jaws (mandibles) used to crush attackers, such as ants.

Nastute soldiers occur in Nasustitermes species and are only rarely found as pests in Victoria. They have a snout from which they eject a sticky solution which irritates and glues attackers.

Phragmotic soldiers have a very large head, which can be wedged in tunnels to block attackers. The drywood termites, which use this strategy, are only occasional introductions to Victoria.

Workers

The workers account for the largest number of termites within the colony, and are therefore responsible for the most damage.

They gather food, groom other termites, construct tunnels and repair damage in addition to tending to the kings, queens and their young. These termites are believed to work 24 hours a day throughout their 4-year life span. Worker termites are generally unpigmented. They are blind, wingless and have undeveloped reproductive organs.

Eggs and young

Termites hatch from eggs that have been tended by their nest mates in specially constructed nurseries.

As soon as they are old enough, the young work within the colony where jobs change with age and maturity.

Colonising flight

Once a single colony becomes sufficiently large it produces winged reproductives which wait in specially constructed chambers until ready to leave the nest and undertake a colonising flight.

They leave the nest as a swarm under conditions of high humidity, still air, and sometimes low light. Termites are not strong fliers and usually only fly up to 1km, although breezes and updrafts can carry them a lot further.

Upon landing near a suitable nest site, the female sheds her wings and emits a calling scent. Males quickly respond.

They dig in and over the next few weeks, mate and take care of their young until enough workers develop to take over the care roles.

New colonies are sometimes established via budding. This is believed to occur when the extremities of the colony lose contact and become independent.

The primary king and queen are believed to emit hormones, which suppress the sexual development of the rest of the colony. However, this control breaks down if the territory is too large or contact with groups is lost.

Termite life cycle

Termites work together in nests or colonies. They hatch from eggs as larvae, which are fed by adult termites. They then develop into four forms or ‘castes’ of termite:

• Alates – have eyes, wings, darker colouring and are fertile.
• Soldiers – have large, dark heads, are blind, wingless, and have undeveloped reproductive organs. Soldiers are tougher than other castes and may take longer to control. Some species of soldier termites have strong jaws (mandibles) used to crush attackers, such as ants.
• Workers – are colourless, blind, wingless and have undeveloped reproductive organs. Workers are the largest caste within a colony and are, therefore, responsible for most damage.
• Reproductives – that are darker in colour to other castes, have functional eyes and robust skin. This caste becomes the leaders of future colonies.

The temperature, food quality, and activity of the colony will determine how long it takes for a termite to develop from egg to adult.

Termite nests

Nests and tunnels are kept moist because worker termites cannot stand low humidity for long periods of time. The temperature within the nursery of a large nest ranges between 10 °C and 35 °C but rarely varies more than one degree a day. The relative humidity is approximately 100 per cent. The moisture required to maintain the temperature and humidity is obtained from the soil, leaking plumbing or decaying timber.

Pest termites

It is important to correctly identify the type of pest termite before beginning treatment. This will help you understand the habits of the colony, locate the nest and indicate the most appropriate method of control.

Termite species are best identified by their soldier termites, which has the most prominent features.

Coptotermes

These termites are widely distributed throughout Victoria, and are responsible for more than 80 per cent of termite damage to buildings.

Coptotermes’ soldiers have brown, saber-like jaws. They measure 3.5–6.5 mm in length. When disturbed, these soldiers eject a white, rubbery glue-like substance from their pear-shaped heads.

A colony of Coptotermes typically includes half a million termites, but may include up to 1 million.

Coptotermes build nests in trees (preferring eucalypts), stumps, under concrete flooring, in wall cavities or enclosed verandahs.

These termites travel at least 50 metres from the colony via a series of underground tunnels to find food. Coptotermes acinaciformis send large numbers to new food sources and, therefore, respond strongly to bait. In contrast, Coptotermes frenchi explore widely for new food sources and feed lightly at multiple points. They respond less strongly to bait.

Nasutitermes

Nasutitermes are found throughout Australia; however, the species are less problematic in Victoria.

Nasutitermes exitiosus is common north of the Great Dividing Range. They construct dark, thin-walled mound nests between 30 cm and 75 cm above ground. These mounds are up to 1m in diameter.

Nasutitermes exitiosus soldiers are most commonly found attacking garden timbers.

Porotermes adamsoni

This is Victoria’s largest species of termite, sometimes called dampwood termite. They are usually found nesting in large pieces of timber (particularly older trees) and are most common in wet, mountainous areas. They may, however, also be found in the dry foothills of Melbourne.

Porotermes tend to live in smaller colonies than other species, and do not construct shelter tubes or travel far underground. They are more easily controlled than other species.

Schedorhinotermes

These termites are found throughout Australia, but only in the north of Victoria.

A mature colony of Schedorhinotermes will have two distinct sizes of soldiers, referred to as ‘major’ and ‘minor’ soldiers. Major soldiers grow up to 5.6 mm long, while minor soldiers are only 3.6 mm long. Both types of soldier have mandibles.

Schedorhinotermes are destructive and relatively nomadic, rather than maintaining a fixed, central nest.

Heterotermes ferox

Heterotermes are widely distributed throughout Australia. However, they are only a major pest species in the Northern Territory.

The soldiers of this species are up to 4.75 mm long, with lengthy, dark jaws and parallel-sided heads.

Heterotermes live in small colonies that attack fence posts, timber flooring, and paling fences within a small radius of the nest. They are commonly found because they feed on small timbers on the soil surface.

Pest termite control – methods

It is preferable to control colonies before installing physical barriers.

Dusts

Dusts work to control termites because they ingest and distribute the insecticide among the colony during habitual grooming.

Insect growth-regulator dusts (such as Triflumuron) and non-repellent termiticides are the safest methods of termite dust control for the human consumer.

Arsenic trioxide dust has been used since the 1930s to control termites, often with the addition of ferric oxide or another colourant. However, arsenic trioxide is a poisonous, highly toxic elemental pesticide that does not degrade.

Bait

Baiting is often the best way to kill an attacking colony when the main nest site cannot be found. Bait stations also allow you to collect samples of termites for species identification.

Bait stations consist of containers of cellulose materials such as timber, paper or cellulose gel which are either buried in the ground near the building under attack or carefully placed inside near known damage.

Bait generally use slow-acting, non-detectable toxins so that the nearly whole colony can be poisoned before adverse effects appear. Repellent termiticide formulations such as those of pyrethroids are not as colony control agents. Care must be taken not to cross contaminate baits with even tiny residues of other pesticides.

Baiting does not provide a useful barrier. The baits do not isolate the building as termites are still able to access the structure. For long-term structural protection, barriers are preferred.

Chemical barriers

This method tries to isolate the termite colony from the building being attacked.

Chemical barriers work by applying an unbroken boundary of pesticide around the exterior of an infested structure. This creates a zone or band of toxic soil that the termites cannot cross. Creating an effective chemical barrier may involve trenching around the foundations of the structure, and injecting the chemical into the soil through holes drilled in concrete foundations.

Termites work through the treated soil unaware that they are picking up a toxic chemical. This greatly reduces the termite population and may destroy the colony.

Repellent chemicals, such as Bifenthrin, are commonly used as barriers. Non-repellent termiticides, such as Imidacloprid and Fipronil, may be more resilient where coverage is uncertain (for example, where the chemical is injected through concrete).

Soil may also be treated with a chemical barrier prior to building construction. Bifenthrin is commonly used for this purpose; Imidacloprid is often used for the exposed perimeter of a new structure.

Physical barriers

Physical barriers are the least-toxic method of termite control for new buildings.

This method isolates the termite colony from a building by creating a complete barrier around or beneath a building’s foundations that termites cannot cross.

Physical barriers can be made of a variety of materials, including:

• Crushed granite of a particular shape and size. Termites cannot get into a building if granite particles are too large and heavy for them to move. Granite aggregate is commonly applied around pipes and behind the lower bricks of a building parameter that has a concrete slab foundation.
• Marine-grade stainless steel mesh can be glued to concrete slab foundations, masonry and around pipes through slabs. Termites cannot enter through the small mesh openings.
• Strip shielding, such as metal ant caps on the tops of stumps under suspended timber floors, can also help prevent termite attack. If installed properly, termites have to construct an easily visible mud tube over the cap to penetrate the building.
• Metal sheeting through brick piers and masonry walls.
• Chemically impregnated sheets that have a repellent termiticide in polymer film or geotextile fabric held between two polymer films. The termiticide dosage is determined by the expected life of the building. Current examples use either deltamethrin or bifenthrin repellents.

Reducing risk of timber attack

Risk of termite attack to timbers may be reduced by controlling moisture, using resistant timbers (see below) beneath floor level, avoiding contact between timber and ground or using non-timber elements in construction (for example, concrete masonry and steel). However, it is notable that research from the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) has shown that rates of termite attack are not related to building frame type; steel-framed homes are also attacked because termites find other food sources inside.

Naturally resistant timber

Certain species of timber, such as Red gum and White cypress pine, are naturally resistant to termite attack. However, all timber cut from a resistant species will not be equally resistant. Accordingly, these timbers may be used in ground contact or for sub-floor framing, but strip shielding or alike should still be used to prevent termites reaching the structure above.

Re-growth timbers of resistant species tend to be less resistant than old-growth timbers and plantation-grown timbers.

Chemically treated timber

Timber treated with copper, chromium and arsenic (CCA) is listed as a restricted chemical product by the Australian Pesticide and Veterinary Medicines Authority (APVMA). This restricts the purchase and use the product, and the areas where it can be used.

Other effective, non-restricted treatments, especially quaternary ammonium compounds, are gradually replacing the arsenic components and have a similar green appearance.

Termite pest control – advice to homeowners

Termites require food (wood) and water keep the humidity within their nests high, and thus, their colony alive. Homeowners can help prevent termite attack by removing these needs.

Pest control operators should suggest ways to do this, such as:

• ensuring soil is not in contact with susceptible building timbers or impinging upon inspection zones
• ensuring subfloors are well ventilated and remain dry
• using only resistant timbers below floor level
• avoiding storage of wood directly on soil, under, around or in contact with buildings
• improving drainage and fixing leaky plumbing to reduce available soil moisture.

Acknowledgements

The department would like to acknowledge the assistance and advice of Don Ewart in the production of this information.