Pests and Sewers

Species found in sewers. To a large extent the species of cockroaches found in sewers reflect the species found above ground in a particular area. Thus, in the Southeast, the smokybrown cockroach (Periplanea fuliginosa) is a common inhabitant of sewers. In New York, German cockroaches (Blattella germanica) are found in sewers, and in the West and Southwest, the Oriental cockroach (Blatta orientalis) occupies some sewers. Perhaps the most widespread species found in U.S. sewers is the American cockroach (Periplaneta americana), which occurs from the Atlantic to the Pacific and from Mexico to Canada. It is commonly found in sewers in northern states where it cannot survive winters outdoors.

Undoubtedly, any of the cockroach species which are found in buildings can also occur in sewers. However, some infestations are somewhat surprising. For instance, the Pennsylvania wood cockroach (Parcoblatta pensylvanica), which is normally free-living in wooded areas, is sometimes found in sewers. And the Turkestan cockroach (Blatta lateralis),which is a recently introduced desert-dwelling insect, has been found in sewers in the states of Texas and California.

How roaches enter sewers. The design and function of sewers makes it impossible to physically exclude small pests such as cockroaches. Risks from buildup of sewer gases require the provision of vents, which allow cockroaches access. Indeed, in places such as San Diego, even roof rats enter sewers via sewer vents on roofs, though these can be screened to prevent rodent entry. Access points for sewer maintenance provide further opportunities for pests to enter, and cockroaches are often found congregating around the underside of manhole covers. And, as with unwanted pets, many cockroaches are flushed down the toilets.

Sometimes, the flushing of cockroaches down toilets follows measures to control cockroaches in the building. Often the occupant sweeps up the "dead" cockroaches and flushes them away. But where the cockroaches have been treated with a product such as pyrethrum, they may have been merely knocked down and not killed, and many subsequently recover in the sewer system.

Where sanitary and surface drainage collect together in combined sewers there are even more opportunities for pests to enter. In such cases, every drain and culvert provides access to the system.

Economic importance. There appear to be no economic benefits from roaches in sewers, but there are several possible disadvantages. Most important, sewer roaches can attain high numbers and serve as population reservoirs from which infestations of above-ground premises can arise. Sewers provide an all-weather route for the spread of cockroaches from one part of a city to another. The importance of sewers as pest reservoirs is indicated by observations in numerous cities throughout the United States that after heavy rains basements with access to sewers have increased populations of American cockroaches. (1) High flows in combined sewers following rain appears to drive cockroaches up into drier areas, where they may become established or re-established.

Sewer-living cockroaches are important from the viewpoint of disease. In "clean" environments, cockroaches may not carry disease organisms. However, it has long been known that several pathogens, particularly Proteus species and Salmonella species, can be isolated from both adults and nymphs of American cockroaches captured near sewer manholes. These cockroaches appear to acquire these bacteria when foraging in the sewers. (2)

For people who service sewers, cockroaches can sometimes be alarming and are a potential cause of accidents. The author once saw a man terrified when he lifted a manhole cover and hundreds of oriental cockroaches clustered on the underside swarmed up his arms and ran all over his shoulders, face and hands. This nearly caused him to drop the heavy manhole cover.

In the case of cockroaches such as the American cockroach, which usually hide their egg capsules, some structural damage may occur in sewers when soft mortar is excavated to insert egg capsules.

Control methods. Controlling cockroaches in sewers can involve localized measures focusing on manholes in individual premises or large scale municipal programs aimed at cockroaches in a large network of sewers. Measures in individual premises will have little effect on the population of cockroaches in the whole sewer system, but they can alleviate invasion of those premises from the sewer. Replacing broken or poorly fitting manhole covers will reduce the passage of many cockroaches, but necessary sewer vents cannot be sealed, and screening against rodents will not prevent passage of cockroaches.

Surface treatments with conventional residual insecticides labeled for cockroach control will kill many passing cockroaches. However, treatments inside sewers should only be conducted with pesticides suitable for this use and preferably with specific labeling for sewer applications. Risks from pesticides in sewers include fish kills here pesticides can pass through the system to rivers or marine environments. In many countries sewers discharge directly to rivers, lakes and seas, while in more developed countries sewage treatment prior to discharge into rivers, lakes and seas cannot be guaranteed to degrade the more persistent pesticides. In addition, where the sewers lead to a sewage treatment plant, it is important that any chemicals introduced into the system do not harm the bacteria used at the plant to degrade the sewage. Where the safety of a pesticide to sewage plant bacteria is unknown, and where that pesticide is not specifically labeled for use in sewers, it should not be used.

Cockroach infestations in sewers have long been a problem in Arizona, and Envirochem of Scottsdale, Ariz., has developed a specialized treatment for sewers. The lacquer formulation of chlorpyrifos, known as Killmaster II, is also cleared for treating sewer manholes and this provides long-term control at the application site, but not between manholes.

For large scale operations involving treatment of manholes and the connecting sewer lines between manholes or along vent pipes, it is customary to use appropriate residual insecticide dusts. Such dusts can be blown down the shafts and travel along the sewer lines, killing every cockroach en route. The use of Ficam Dust is particularly popular in municipal cockroach control programs for sewers.

In the past, one traditional way of dusting sewers was to use power dusters to inject dust down one manhole and to keep applying until dust emerged from an opened manhole 100 to 200 yards away. This procedure would be repeated along the required length of the sewer line. Nowadays, more specific limits are placed on how much dust is blown down each manhole. For instance, the label for Ficam D states: "Apply 7 oz. of Ficam D per manhole using a power duster for knockdown and short-term population suppression. Where longer residual control (30 days) is desired, apply 14 oz. of Ficam D per manhole." In practice, where whole systems are treated with Ficam D, applications need to be repeated only once or twice a year.

The use of insecticide dusts to penetrate sewer lines avoids the need to open and treat every manhole shaft and thus saves time. In any case it is seldom practical to individually treat every manhole because of jammed covers or parked vehicles.

The use of sticky traps fastened to the underside of manhole covers can help determine the effectiveness of treatments and the frequency of retreatments. Sewer maps are an essential tool in the planning and follow-up of large-scale programs. Wherever possible insect control programs should be coordinated with rodent control and sewer cleaning programs.

Safety issues. Apart from the pesticide safety aspects already mentioned, the matter of physical safety of pest management personnel must also be considered. Sewers are intrinsically dangerous places, and wherever possible methods of pest treatment and inspections should be chosen which don’t require entering sewers. If entry into manholes is required, full safety precautions should be taken. In this regard, the label for Empire 20 states: "Persons applying this product in the manhole must wear chemical resistant gloves, a respirator approved by NIOSH for organic chemical vapors, goggles and long-sleeved clothing." This author would also recommend that nobody should work alone inside a manhole. Some safety aspects, such as using the proper tools for lifting manhole covers and protecting open manholes from traffic and pedestrians, are obvious. But even small mistakes can be very dangerous. The author once fell down a manhole at night because the manhole cover had not been properly replaced. When he walked on it, the cover flipped over and the author suddenly found himself hanging by his bruised elbows from the pavement! However, when conducted carefully and with the right materials and methods, cockroach control in sewers is a valuable component of urban pest management.

___ Keith Story

The author is a frequent contributor to PCT magazine. He is president of Winchester Consultants, formerly of Winchester, Mass., but now based n Winchester, England.

1. Schoof, J.F., and R.E. Siverly - 1954. The occurrence and movement of Periplaneta americana

within an urban sewerage system. Amer. Trop. Med. And Hyg. 3(2): 367-371.

2. Bitter R.S., and O.B. Williams - 1949a. Enteric organisms from the American cockroach. J. Infect.

Dis. 85: 87-90. 1949b. Enteric organisms from the American cockroach. Soc. Am. Bact.

Abs., 49^th Gen. Mtg., P.80.