Control of American cockroaches (Dictyoptera: Blattidae) in sewer systems

Abstract:
American cockroaches, Periplaneta americana (L.), left undisturbed, often develop to enormous numbers and become major pests in sanitary sewers throughout much of the world. They are also domiciliary pests in many places, especially in southeast Asia. Moving from sewers, they often invade surrounding streets and buildings, and have been implicated as being associated with allergy and disease. They are particularly troublesome in metropolitan areas where manhole maintenance is neglected for long periods. As the use of chlorpyrifos and diazinon for cockroach control has been discontinued in many parts of the world, municipalities are seeking to use approved IPM strategies and only materials with low mammalian toxicity and minimal environmental impact. Various sprays, dusts and baits registered in the U.S. are used to control P. americana, but there is little evidence as to their efficacy in sewers. Neonicotinyl baits provide rapid, effective and relatively inexpensive control of American cockroaches in sewers. Both fipronil, 0.05% gel bait (MaxForce FC Roach Killer) and imidacloprid, 2.15% gel bait (Pre-Empt, IMAGEL) provided 96 to 99% control for 6 months or longer. Treating adjacent manholes whether they contained cockroaches or not broadened the sphere of effect, probably by reducing the likelihood of cockroaches using adjacent untreated holes as refuge. Effective treatment consisted of applying the gel as a narrow band circumscribed just below the cover, not deep within. Gel bait dispensed from cards or solid and granular baits dispensed from devices lower in the manholes were not as effective. Although covered with fungus, gel baits retrieved from manholes months later remained toxic, suggesting prolonged efficacy against nymphs which subsequently emerge. Resurgence of populations in some manholes appears to occur as a result of all the bait having been consumed rather than from degradation of AI. Fipronil, 0.01% gel bait provided only 40 to 50% control, suggesting that the 0.05% rate is near the lower limit of its performance. A similar rate-dependency is likely for imidacloprid. As little as 50-100 g/manhole of a proprietary dust consisting of 2.0% pyrethrins, 10.0% piperonyl butoxide, 35.5 % boric acid, and 50% diatomaceous earth blown into the system with a commercial DeVilbis sprayer provided > 98% control for at least 3 months. The advantage of this technique was that lateral lines and adjacent manholes could be treated. This technique did, however, require specialized equipment. Release of up to 800 per manhole of the parasitoid Aprostocetus hagenowii (Raxeburg) had no measurable effect on cockroach populations. This parasite is reportedly effective on P. americana and the smokybrown cockroach, P. fuliginosa, in other areas, but its lack of effectiveness here suggests that the sewer environment may be inappropriate for this insect.