Argentine Ant (Linepithema humile) Integrated Pest Management Plan
This document contains information about the biology and management of the Argentine ant. A wide range of management options is listed. From this list, the IPM Practitioner can choose options to develop a unique management plan for each particular customer site.
Management Objectives for the Pest at the Particular Site
What do you want/need to accomplish at the site in regard to the Argentine ant management?
The answer to this question will vary, depending on the site and the customer. Some examples are
- Reduce ant complaints in the building and work with occupants to prevent future invasions
- Keep ants out of computer room and educate computer techs on why ants invade
- Pull ants out of building, reduce possibility of future invasions by educating building
- occupants and reducing the ideal habitat that currently exists next to the building.
- Keep ants out of the house 90% of the time and work to reduce ant access to house.
Argentine Ant Identification
- Workers are all the same size, around 1/8 inch long
- Uniformly dull brown in color
- Single node ant, petiole with 1 erect node
- Thorax is uneven, not smooth, when viewed from the side
- If a single ant is crushed, it has little smell
- If a large number of ants are crushed, they have a musty smell
- The smell of an Argentine ant is very different from the rotten coconut odor of an odorous house ant
Why the Argentine Ant is Considered a Pest
- The Argentine ant is mainly a nuisance pest that trails into buildings in search of food or nesting sites
- It does not sting
- Occasionally it may bite, but the bite is a mild pinch
- This ant is not a vector for any diseases of people
- Argentine ants cultivate plant sucking pests so their presence in a landscape may damage plantings
Special Regulatory Conditions
There are no special regulations that pertain to this ant.
Biology and Behavior of the Argentine Ant
To be successful, management strategies must take into consideration the biology and behavior of the pest. Understanding the biology of a pest can reveal weaknesses and vulnerabilities that can be exploited when trying to manage the pest.
- The Argentine ant is not native to the U.S. It probably came on Brazilian coffee ships to New Orleans in the late 1800‘s.
- In 1918, J.R. Horton wrote in a USDA Bulletin that he and his colleagues had trapped 1.3 million Argentine queens and collected 1,000 gallons of brood.
- This ant was first found in California in 1905, in Ontario. By 1908 it had spread through the citrus growing regions of the state to San Francisco.
- In the most urbanized areas of California, the Argentine ant has replaced all native ants.
- Argentine ants may be capable of carrying pathogenic bacteria in hospitals and food establishments.
- Ants have 4 life stages: egg, larva, pupa (cocoon), and adult. Queens lay eggs that hatch into small larvae. The larvae grow as they are fed by the adult worker ants who are all female. When the larvae are grown, they change into pupae. During the pupal stage, the pupa changes into an adult ant.
Argentine Ant Colonies
- Colonies are linked by tunnels; workers and queens move freely from nest to nest; each colony has many queens that live in harmony. Perhaps it is more accurate to think of Argentine ants as living in huge colonies with 1000‘s of entrances.
- Because of these huge “supercolonies,” ‖ the concept of finding and killing “the” nest is not always valid.
- The energy that most other ant species use in defending the colony is used instead for reproduction.
- Adult worker ants (all females) feed and care for the young, but also feed each other and the queens.
- Up to 50% of the food workers ingest is shared with fellow workers. The technical term for insects exchanging food with one another is trophallaxis. This is the way baits are spread throughout a colony.
- Adult ants feed only on liquids, but they collect solid food for larvae (the immature stage) living in the nest. Larvae digest the solid food and produce liquids for the workers to feed on.
- On average at any one time, a very small proportion of a colony is out foraging for food, so killing these ants will not eliminate the colony.
- Argentine ants will forage 200 ft. away from their nest.
- Argentine ants feed on just about anything from dead animals (including insects) to all kinds of human and pet food.
- A favorite food is the honeydew produced by insects like aphids, mealybugs, scales, and whiteflies. Argentine ants protect these insects from their natural enemies.
- Plants that harbor these pests and are growing near a structure will attract ants to the building.
- If ants are excluded from plants with honeydew-producing insects, natural enemies will often eliminate the plant pests.
- Liquid baits with sugar as the attractant are useful throughout the year, because adult ants will always feed on sugary liquids.
- Baits with a protein attractant may only be useful when the colony is expanding and ants are feeding a large number of young.
Development of the Colony through the Seasons and Baits Likely to be Taken Each Season
Winter (November thru January)
In winter, many adults die and the colony essentially stops breeding. The ant population is small.
- Liquid sugar baits are accepted better than other baits and less is needed because of the lower population.
Late winter/early spring
In late winter and early spring, breeding increases and adult workers seek honeydew producing insects (aphids, scales, mealybugs, and whiteflies) and protein to feed developing larvae.
- Both solid protein and liquid sugar baits are accepted.
Honeydew producing insects decline (beginning in July/August), and ants start to look elsewhere for food, often in nearby buildings.
- In early summer, solid protein baits are still accepted.
- Liquid sugar baits are readily accepted all summer.
The ant population has reached its maximum, honeydew food sources have declined and foraging pressure results in more nearby building invasions.
- Sugar baits readily accepted.
- Argentine ants move their colonies within hours to take advantage of a food source or to escape inhospitable conditions. In winter they look for places that are warmer and drier, and in summer they seek cooler and moister sites.
- Their shallow nests are primarily in the ground, and they are not marked by significant soil mounds. They prefer moist, well-drained soil.
Outside, ants nest
- near irrigated turf and other landscaping
- in planters and potted plants
- in the ground under trees, especially trees with honeydew producing insects,
- near faucets and irrigation valves
- under sidewalks, stones and patios
- in soil accumulated in the corners of a roof
Inside, ants nest
- In potted plants
- inside cupboards and drawers
- under tiles on kitchen counters, behind wall tile and brick veneer
- in the insulation in dishwashers, washing machines, and refrigerators,
- in wall voids, in moist basements, and in vehicles
- in unusual places such as inside metal curtain rods
Landscape factors that favor the Argentine Ant
- Damp and/or disturbed soil
- Soil in potted plants
- Mulch such as shredded bark, pebbles, small stones
- Vegetation that supports honeydew-producing insects such as citrus, pines, bottlebrush, birch
- Soil that is kept warm by the thermal mass of a sidewalk, flagstone walk or patio, decorative rock on top of black plastic
Monitoring and Record Keeping
The purpose of monitoring is to track pest activity in order to catch small problems before they become overwhelming. Monitoring also makes it possible to properly time pest management actions and to evaluate the effectiveness of those actions. Records are kept to document the methods and products used and to record information that can be used to fine-tune pest management methods and plan future actions.
Visual inspection is the most effective means of monitoring for Argentine ants.
The “tolerance level” is the number of Argentine ants that triggers action to control the pest. The tolerance level is site-specific and differs depending on the customer, the location, and other factors. Determining the tolerance levels for a site helps prioritize work that must be done to manage the pest.
Pests need food, water, and shelter to survive. Pests also need access to a structure to make themselves a nuisance inside a building. If even just one of these factors can be reduced (or eliminated), the environment will support fewer pests, and pests will be less likely to invade our living spaces.
Outdoors: To limit availability of food
- Take pet food dishes inside immediately after pets have eaten. Wash pet food bowls.
- Discuss the importance of not feeding feral cats with those who may want to do so.
- Thoroughly rinse recyclables that will be stored outdoors.
- Store garbage, especially garbage containing food wastes, in garbage cans or dumpsters outside the building.
- Treat honeydew-producing insects on vegetation near the structure by washing with plain water or with insecticidal soap and water. Aphids, scales, mealybugs, whiteflies, and psyllids are examples of honeydew-producing insects.
Some plants that are highly attractive to honeydew-producing insects are:
- Bottlebrush bush
- Chinese elm
- Conifers (pines, redwoods)
- London Plane tree (sycamore)
- Use sticky barriers around trunks to exclude ants, and trim branches that touch the building, the ground, other plants or structures to prevent ants from finding an alternative route into the plant.
- Remove and/or replace plants that regularly have large populations of honeydew-producing insects.
Outdoors: To limit availability of shelter/habitat
- Reduce excessive moisture and irrigation leaks near structures.
- Reduce areas covered with black plastic and decorative rock, especially next to the foundation.
- Reduce or eliminate bark mulch close to the structure.
- Cut back or eliminate ground covers next to the structure. This will also allow Pestec to have access to the foundation to observe ant activity.
Inside: To limit availability of food
- Thoroughly clean food preparation and eating areas daily.
- Discuss importance of sanitation with appropriate people
- Regularly steam clean large appliances in commercial kitchens.
- Store food in the refrigerator, freezer, or cooler, or in ant-proof containers such as Tupperware or screw top jars (screw-top jars are not ant-proof unless the lid has a rubber gasket).
- Use plastic liners in wastebaskets and garbage cans
- Remove garbage containing food wastes from building before nightfall or tie a knot in the plastic liner.
- Set small garbage cans on ant-proof stands such as the Antser® (platform with soapy water moat underneath)
- Wash pet bowls immediately after pets have eaten or place pet dishes on ant-proof stands such as the Antser®(platform with soapy water moat underneath).
- Store dry pet food in ant-proof containers, sealed plastic bags or seal pet food bag in such a way that ant have a hard time getting in (fold top of bag and forth and seal with a clip).
Inside: To limit availability of shelter/habitat
- Remove potted plants with ant nests
- Place potted plants on ant-proof stands such as the Antser® (platform with soapy water moat underneath)
- Place potted plants in a moat of soapy water: place plant on a small overturned saucer inside a larger saucer; add water to the larger saucer along with several drops of liquid detergent.
Physical controls employ physical means to remove ants or prevent their access to a structure.
Inside and Outdoors: To remove ants
- Vacuum up ant trails.
- Pick up ants with a sticky lint roller
- Clean up ant trails with soap and water
Outdoors: To limit access to the structure (pest-proofing)
- Trim trees and bushes touching the structure
- Caulk or otherwise seal entry points where ants are getting in or have been seen getting in, especially around plumbing and wiring. Not all holes in a structure need to be sealed to make a difference in the number of ant invasions.
Inside: To limit access to the structure (pest-proofing)
- Caulk or otherwise seal entry points that ants are currently using or that are nearby. Not all holes in a structure need to be sealed to make a difference in the number of ant invasions.
- Insert foam insulator sheets behind electrical face plates to seal off ant access and reduce infiltration of hot or cold air.
- Blow low-toxic insecticidal dusts into cracks and wall voids
Chemical controls are used to directly suppress the ant population; however, with Argentine ants, it will never be possible to eradicate them from any particular area. There are too many ants nearby that will simply move in to fill the empty habitat. The goal of ant management is to prevent the ants from becoming a nuisance to the people living and working in a structure.
- Baiting is the preferred chemical control method for Argentine ants.
Why use baits?
- Baiting may take longer to kill ants, but will have a much greater impact on the colony as a whole, because ants take bait back to feed to their nest mates. Sprays kill only a small fraction of the ants that are out foraging, and the foragers only represent a very small fraction of the total colony.
- Spraying pesticides around the outside of a structure can lead to run-off that contaminates creeks, rivers, and the Bay.
- Baits are used outdoors to draw ants out of a structure.
- Inside, baiting is also the preferred chemical control method for Argentine ants.
- Inside, baits will be left only long enough to stop the trail of ants entering the building. At that point the bait stations will be removed in order not to attract more ants.
Note: Do not spray pesticide on or near ant bait stations because the pesticide will repel the ants.
- If ant populations are high, or invasions persist, and placing a bait station at the exterior perimeter of the building is not feasible, a low-toxic and/or repellent insecticidal dust will be applied to cracks, crevices, wall voids, electrical boxes, conduits, etc. If necessary, insecticidal dusts will be used to spot-treat under the edge of carpets and behind baseboards.
The IPM Partnership
The PCO-Customer Partnership is Very Important
IPM works best when the customer and Pestec form a partnership to tackle the pest problem. Pestec will discuss the findings of the initial inspection and any subsequent monitoring sessions with the customer to determine which issues and tasks will be the responsibility of Pestec and which will be the responsibility of the customer.
Information is a powerful tool in IPM. Information can help change people’s behavior, particularly in how they store food and dispose waste. Changing these behaviors is often an invaluable part of managing ants. Building occupants and homeowners can also help in the early detection of pests so that Pestec can be alerted before the problem is severe. Pestec’s highly trained and knowledgeable staff can provide pest management education or training sessions for facilities managers, risk managers, building occupants, homeowner association, and others.