[Ant Control Issue] Fracture!

By Editor’s note: “Urban Ants of North America and Europe: Identification, Biology, and Management” will be published this fall. The book’s authors are John Klotz, University of California, Riverside; Laurel Hansen, Spokane Falls Community College; Reiner Pospischil, Bayer CropScience Aktiengesellschaft; and Michael Rust, University of California, Riverside. References have been removed from this text to improve readability. To order the book, visit www.pctonline.com/store or call 800/456-0707.

In recent years, ants have been consistently ranked as the number one pest by the structural pest control industry, surpassing termites, cockroaches and rodents. It is estimated that in the United States alone, ant control generates almost $2 billion annually for pest management professionals. If the red imported fire ant were to spread throughout California, a conservative estimate of the total financial impact on households would be $342 million. In fact, the threat was so real that residents of Orange County, Calif., recently approved an increase in property assessments in part to control red imported fire ants. Surveys indicate the preeminence of ants as household pests and homeowners regard them as more troublesome than cockroaches.

Ants present a particular challenge to the PMP because there are so many different species, each with their own unique habits and methods of control. The identification of some ant species challenges even the best extension specialist and PMP. Consequently, in our book, we have provided comprehensive but workable keys to ants likely to be encountered in urban environments. Illustrations focus attention to those morphological features that permit rapid identification. The species vary depending on the geographic location, with some “tramp ants” having worldwide distribution. Some species, such as the eastern black carpenter ant, Pharaoh ant or odorous house ant may nest within the structure; whereas others, such as the Argentine ant, nest outdoors. Others, such as the fire ants and harvester ants, may be found in landscaped areas surrounding homes, parks and recreation areas. Behavioral and ecological habits that assist in recognition have also been emphasized. Recognition of these species and their habits are essential to good management.

While gathering the information for this book, it became quite apparent that there is a lack of practical information available on most urban pest species. Knowledge about the control of urban pest ants is limited to a few species such as Argentine ants, carpenter ants, fire ants and Pharaoh ants. Comprehensive Integrated Pest Management programs exist only for red imported fire ants. We hope that the book from which this article is excerpted will stimulate other researchers and PMPs to study these other species. Consequently, the book is not intended to provide a “cookbook” approach to control, but rather serve as a reference and a starting point for the PMP or homeowner to design their own control program.

One of the prime movers in this arena has been Stoy Hedges, who has provided the most comprehensive approach to ant control to date for pest management professionals. Indeed, his Field Guide for the Management of Structure-Infesting Ants (www.pctonline.com/store) is a landmark publication in this regard. Stoy has dedicated his career to educating the pest control industry on good pest management practices, not only for ants but many other structural pests as well. We hope that our efforts follow in his path. It is in this spirit that we, therefore, dedicate our book to him for all his noteworthy efforts and contributions to this challenging, rapidly changing and ever-evolving field.

What follows is a description of the Pharaoh ant (Monomorium pharaonis), its biology and habits, and control techniques.

IDENTIFYING CHARACTERISTICS. Pharaoh ant workers are about 2 mm long, monomorphic and have a two-segmented petiole. Their antennae are 12-segmented with a three-segmented club. They are yellowish or light brown to reddish, with the tip of the gaster darkened. They possess a stinger, but are unable to sting, instead using it to dispense pheromones. Queens are similar in color to workers but about twice their size. Males are black and about 3 mm long. Pharaoh ants are often confused with thief ants; however, thief ants have a 10-segmented antenna with a two-segmented club.

DISTRIBUTION. Linnaeus described a specimen from Egypt in 1758. Various tropical points of origin have been postulated for Pharaoh ants including South America, Africa and India. They have spread throughout the world via international trade and in the U.S., the Pharaoh ant probably occurs in every town or city of commercial importance. Some of the places they have been collected include Europe, Japan, Central and South America, Australia, New Zealand, India and Saudi Arabia.

Pharaoh ants have been established in Europe for more than 100 years, surviving only in continuously heated buildings and are now found in all European countries. Their populations have been on the increase over the last 15 years in Switzerland, particularly in apartment buildings. However, their incidence in hospitals and food-production facilities has been relatively low. In Denmark, reports of Pharaoh ant infestations to the Danish Pest Infestation Laboratory have declined markedly over the last 15 years due to Internet access to management techniques and the development of more effective baits. Pharaoh ants are widely distributed in the Czech Republic and Poland, where they commonly infest apartment buildings.

BIOLOGY AND HABITS. Pharaoh ants are considered “tramp ants,” which are characterized by their transient nesting behavior and ability to propagate by fission or budding. Indeed, their notoriety in pest control derives from this predisposition to form “satellite” colonies throughout structures. Application of repellent residual insecticides can trigger the splintering of a colony into numerous satellite colonies and in cases where treatments are applied repeatedly, an infestation can spread throughout an entire building complex.

Even in the absence of repellent insecticides, a localized infestation of Pharaoh ants can spread quickly due to inadvertent transport by humans. As few as five workers and 50 pieces of brood (eggs, larvae and pupae) can give rise to a colony of 10,000 workers in a little over a year and new reproductives can be produced by these queenless propagules. Mature colonies are polygynous, polydomous and unicolonial and mating takes place within the nest.

The queens obtain nourishment primarily from larval secretions and their fecundity is directly related to the number of large larvae in the nest. If the queens do not obtain these larval secretions then ovariole uptake of vitellogenin is inhibited and oogenesis ceases. There is also a group of replete workers that store these larval secretions in order to provide food for the queens when the larvae are few in number.

In cooler climates, Pharaoh ants nest indoors, whereas in warmer climates they can forage and nest outdoors. In central Europe, for example, they are found only indoors and are spread to other buildings by transport in items such as furniture, laundry and electronic equipment. In selecting nest sites, they are opportunistic and will occupy any crack or crevice with sufficient warmth and humidity. In homes, they are often found in kitchens and bathrooms near sources of water. Typically, their nests are located in inaccessible areas, such as within interior or exterior wall voids, under floors, behind electric outlet plates in bathrooms and kitchens, and behind baseboards or windowsills. In health-care facilities, they are considered a risk because of their ability to transmit disease organisms such as Pseudomonas, Staphylococcus, Salmonella, Clostridium and Streptococcus. In hospitals, Pharaoh ants have been known to infest intravenous units and enter sterile packages and wound dressings.

Pharaoh ants forage both day and night, often going undetected because of their small size and cryptic habits. Within structures, their trails are often hidden behind baseboards, cabinets and walls where the ants travel on wires and pipes, sometimes becoming evident when they emerge from electrical outlets and plumbing fixtures. Outside, their trails are often found around windows and doorways and following structural edges. Their foraging range in and around structures can be extensive. For example, in one study, Pharaoh ants were fed dyed bait in a military housing complex and tracked as far as 45 meters from the bait. Dyed ants were found foraging both inside and outside the complex and on different floors.

The principal component of their trail pheromone is faranal, which is produced by the Dufour’s gland. Surprisingly, the trail is polarized and based on its geometry provides Pharaoh ants with directional information. It is the only case of trail polarity that has been demonstrated in ants. In addition, Pharaoh ants deposit a repellent pheromone on trails to discourage other ants from using a trail that is not rewarding.

Pharaoh ants are omnivorous and feed on various sources of fat, protein and carbohydrate, as well as scavenge and kill small insects. In laboratory experiments, researchers showed that Pharaoh ants have an “alternation” and “satiation” response to food, i.e., when colonies were given a choice to feed on carbohydrates or proteins, those that were fed protein for several weeks chose the carbohydrate whereas those fed carbohydrate chose the protein. In addition, ants that were provided with a preferred food for several weeks, switched to other foods when offered a choice. These feeding behaviors promote a balanced and varied diet for the Pharaoh ant.

CONTROL. The research and development of methods to control Pharaoh ants has yielded several critical insights. One of the more significant findings is that repellent insecticides cause Pharaoh ant colonies to fracture into satellite nests. Consequently, application of repellent sprays can be counterproductive. An exception to this rule is when the nests are accessible to treatment, for example in a potted plant. In contrast, nonrepellent residual insecticides can be used effectively in Pharaoh ant control without fragmenting colonies.

The development of baits for Pharaoh ant control is a major success story. The research laboratories of J.P. Edwards with the Ministry of Agriculture in England and D.F. Williams with the USDA-ARS in Gainesville, Fla., made substantial contributions to our understanding of Pharaoh ant behavior and its importance in bait efficacy. Oi et al, for example, showed that bait containing an insect growth regulator (pyriproxyfen) is distributed by the ants more thoroughly between colonies than bait containing a metabolic inhibitor (hydramethylnon). Thus, more bait placements are necessary when metabolic inhibitors are used. In structural infestations where Pharaoh ants are foraging both inside and outside, outdoor applications of bait are sufficient to obtain control. Baiting programs should include procedures to monitor for changes in food preference because of the phenomenon of bait-switching in Pharaoh ants.

A thorough and systematic application of baits is required in Pharaoh ant control. The first step in a comprehensive baiting program should be a pretreatment survey to determine where the ants are located. A dab of raw peanut butter or honey on white index cards can be used for the survey. The peanut butter can be applied with a large, 60-cc syringe with the needle tip removed. The baited cards should be placed at potential food and water sources inside the structure in cooler climates and both inside and outside in warmer climates.

In an apartment complex, for example, survey cards should be placed in apartment units and in lobbies, kitchens, laundries, lounges and offices. At least 8 to 16 cards should be placed in each unit (usually two to four each in the kitchen, living room, bathroom and bedroom). Survey cards also should be placed where tenants have seen ant activity. Windowsills in the living room and bedroom of each apartment are ideal spots for survey cards, because dead insects on windowsills attract foraging ants and the numerous cracks and crevices around window casings are ideal nest sites.

In the kitchen and bathroom, cards should be placed near sources of water, such as pipes and drains, sinks, countertops and toilets. Outside, survey cards should be placed near windows, around entrances and exits and incoming and outgoing plumbing lines. It is important to position the cards along edges or other structural guidelines, where the ants are likely to travel. These cards should be left undisturbed to allow ants to locate and recruit foragers to the attractant, which can take one to several hours. The number of worker ants on each card should be estimated and recorded on an inspection diagram.

The pretreatment survey locates where the ant activity is concentrated so that toxic baits can be placed strategically. It will also assist one in finding small isolated colonies that otherwise might be overlooked and could result in continued infestation. Where feeding is recorded at survey cards, the trailing ants may be traced back to where they are entering from a crack or crevice, switch plate or pipe flange. Such entrance sites should be noted on a diagram for later placement of bait. Since Pharaoh ants typically travel on wires and pipes, baiting every switch plate and pipe void in each room with ant activity is recommended. Additionally, baiting outside is important because a considerable number of Pharaoh ants forage outdoors during warm weather.

A good floorplan of the infested structure is useful to display survey data and locate bait placements. A floor plan also helps in estimating the quantity of bait or number of bait stations needed. For an average size room, four to six bait placements may be sufficient, but it is important that every ant trail be baited so additional placements may be necessary. A building with a long history of Pharaoh ant activity combined with attempts at control using repellent residual insecticides will take more effort, bait placements and time to achieve control. In such cases, a year or longer may be required to find and bait all ant colonies that may be deeply hidden within voids.

When ants are attracted to the bait and are committed to feeding on it for an extended period, success is probable. Pharaoh ants, however, have a tendency to switch their food preferences so it is important to provide sweet liquid baits or a variety of protein or oil baits as a choice. Foragers may tire of one kind of food and, if offered a choice, switch to another.