The Pharaoh ant (Monomorium pharaonis) is an introduced species that exhibits several tramp ant characteristics, such as:
- Generalist diet: feeds on sugars, fats, and proteins
- Polygyny: presence of two or more egg-laying queens in one colony
- Polydomy: presence of multiple nests
- Large colony size: up to 300,000 individuals
- Opportunistic nester: will nest in any site that provides protection
- Close association with humans: protection within heated structures, easy access to food
- Budding: multiplication of colonies by the departure of one or more reproductive forms
These traits make colonies of Pharaoh ants successful invaders of human-built structures and also make them extremely difficult to eradicate. Of the habits listed previously, reproduction by budding is perhaps the most critical to the success of Pharaoh ants.
While the majority of ant species disperse and start new colonies by individual females following a mating flight, Pharaoh ants mate in the nest and propagate by fragmentation of mature colonies. Thus, new colonies are created independently of colony reproductive cycles and may be initiated at any time.
During budding, a reproductively competent colony fragment migrates to a new location to establish a new nest, which may or may not remain in association with the parent colony. In the case of Pharaoh ants, new colonies may be initiated with a group of about 50 workers and at least one queen and/or larvae. However, queens are not essential for the successful foundation of new colonies as workers can rear new queens from existing larvae.
Traditionally, part of the success and persistence of the Pharaoh ant had been attributed to its frequent budding habits.
ALL ABOUT BUDDING. Budding is common in ants with many queens including Pharaoh, odorous and Argentine ants and may occur due to a wide range of factors, including:
- Overcrowding
- Response to weather: seasonal changes in a structure’s central heating and cooling system
- Physical disturbance: movement of furniture, shelves, etc.
- Dietary change: depletion of or discovery of new resource
- Chemical disturbance: application of a repellent pesticide
Traditionally, applications of repellent spray insecticides or dusts have been alleged to be the major factor promoting fragmentation of colonies. Such treatments repel ants, forcing more colonies to form through budding while killing only a small number of ants.
In addition, residual insecticides are usually ineffective for complete colony elimination because they only affect foraging workers and fail to reach reproductive individuals. As a result, bait treatments are generally recommended for Pharaoh ant control. As part of an experiment we performed at Purdue University, we were interested in testing the concept of baiting to determine the ability of baits to achieve control of all life stages.
TEST DESIGN. Entire colonies of Pharaoh ants were established from lab colonies using 250 workers, 20 mg of brood and 2 queens. Although these are small colonies relative to field colonies, all stages are represented and allow for normal ant behavior. Each test colony was provided a single bait treatment.
Separate colonies were established and provided a lab diet to serve as untreated controls. Mortality of workers and queens was assessed at one, three, five and seven days after treatment. If the insecticide is readily transferred through trophallaxis, we would expect to see mortality among the queens relatively quickly.
RESULTS/CONCLUSIONS. The bait treatments provided control of workers. DuPont Professional Products’ Advion ant bait arena had more than 80 percent mortality after just 1 day. At first glance this may raise some concern about the ability of foragers to effectively distribute toxicant to other castes and/or life stages.
However, in this test, queen mortality with Advion was also significantly higher than the untreated control at 30 percent on day one. By day seven, 100 percent of the workers and 100 percent of the queens in the treated colonies were controlled with Advion.
This strongly suggests that foragers are transferring bait material, including toxicant, to reproductive stages quickly. This may be unique to the formulation of Advion and/or the active ingredient indoxacarb as we have not seen this effect previously. Oi and Oi (2006) observed the same quick and thorough control of red imported fire ants when evaluating Advion fire ant bait in lab and field testing.
CONCLUSION. As demonstrated in this research, baits can be effective at providing quick, thorough control of all stages of a Pharaoh ant colony. This is one of the significant advantages of using bait products for ant control. When pest management professionals are considering options for the treatment of ant infestations, based on this research at Purdue University, baits should be high on the list as a complement to other applications or possibly as a standalone treatment.
Reference
Oi, D. H. and Oi, F. M. 2006. Speed of efficacy and delayed toxicity characteristics of fast-acting fire ant (Hymenoptera: Formicidae) baits. J. Econ. Entomol. 99:1739-1748.
Grzegorz Buczkowski, Ph.D., is a research assistant professor in the department of entomology and director of the Industrial Affiliates Program at Purdue University. Gary W. Bennett, Ph.D., is a professor in the department of entomology and director of the Center for Urban and Industrial Pest Management at Purdue University. Clay W. Scherer, Ph.D., is global product development manager, DuPont Professional Products. Contact the authors at gbuczkowski@giemedia.com, gbennett@giemedia.com and cscherer@giemedia.com, respectively.
10 Tips for Successful Management of Pharaoh Ants
1. Since Pharaoh ants may nest in unusual places, pest management professionals should inspect all areas conducive to infestation.
2. Since Pharaoh ants follow chemical and structural guidelines to find food and water, pest management professionals should place baits close to foraging trails.
3. Since Pharaoh ant colonies are comprised of many small nests, pest management professionals should put out numerous baits to reach the entire population.
4. Since Pharaoh ant colonies may be dispersed throughout an entire building, pest management professionals should treat all active and suspected foraging sites.
5. Since Pharaoh ants disperse easily, pest management professionals should use baits rather than liquid spray chemicals.
6. Since Pharaoh ant queens lay an enormous amount of eggs, pest management professionals should target the queens with baits to achieve complete colony elimination.
7. Since Pharaoh ant trails may not always be obvious, pest management professionals should use pre-baiting to identify “hot spots.”
8. Since Pharaoh ant colonies are very mobile, pest management professionals should adjust bait placement according to foraging patterns.
9. Since Pharaoh ant colonies may nest outside in warmer climates, pest management professionals shouldn’t forget to bait outside.
10. Since Pharaoh ant colonies can rebound with just a few workers and some brood, pest management professionals should use baits persistently for complete colony eradication.