Cockroach E-mail
alt Few pests conjure up such strong feelings of distress, embarrassment and disgust as do cockroaches. Chemical control seems the obvious solution, and is still a common sight. This method is not always necessary as some domestic cockroach problems can be controlled without reliance on pesticides.

Cockroaches have changed little over the last 280 million years, and are often associated with unclean environments and as potential vectors of disease. There is limited proof that cockroaches are involved in the transfer of human pathogens, however recent research suggests a link with allergies such as asthma.(1)

The two most common varieties cockroach found in Northern Europe are the German (Blattella germanica) and the oriental(Blatta orientalis). The oriental cockroach is 32mm in length with a dark red-brown-black colour throughout and lives for approximately 4-5 months. It is u usually found below ground level, in drains and sinks, and under refrigerators and washing machines. The female produces egg capsules at monthly intervals which contain up to 16 eggs and deposits them in debris or food under sheltered areas. It takes between 10 months to two years for the egg to reach the adult stage, because the life cycle takes this long to complete, severe infestations should be avoidable with good hygiene practices.

The German cockroach is approximately 14mm in length, is light brown in colour and has two dark stripes on the section of the thorax behind the head. The female produces an average of four egg cases during its life-span containing between 30 and 50 eggs and carries the case until 12 days before hatching. It takes between 3-4 months for the egg to pass through the nymph stage and reach the adult stage of the life cycle which lasts for more than 200 days. Because of their small size, the large number of eggs per case and the speed with which they mature, the German cockroach tends to be more prolific than the oriental cockroaches.

Natural cockroach control
Monitoring programmes should be in place before, during and after any efforts in dealing with a cockroach infestation. This tells you how large the problem is, where the main concentrations are and how effective the strategies in place are working. You can make your own pesticide free trap using a jar with a slice of white sandwich bread inside. A coating of petroleum jelly on the inside of the jar mouth will cause the cockroaches to fall in and also stop them from escaping. They can then be killed with hot soapy water or by placing them in the freezer overnight.
Placement of sticky traps are another non-chemical form of trapping. Recent research has shown that with the addition of aggregation and sexual pheromones, sticky traps can be made much more effective. Studies show that the Victor Roach Pheromone trap(2) was just as effective for cockroach control as toxic residual sprays. Examples reported in the US trade magazine Pest Control Technology have shown that these traps successfully controlled an infestation in a Boeing 747 aircraft in Israel and reduced the cockroach population in a US government infested kitchen by 95% in two weeks.(3)

Close, warm, moist environments are perfect for cockroaches, so underneath refrigerators, near plumbing systems and in any cracks and crevices are where they are most likely to be found. They like to travel around the edges of rooms and other objects, so placement of traps should be along these routes. Traps should be out for at least a week to get a reliable indication of the problem. Cockroaches seek cover during the daytime and are most active at night.

Good hygiene practice is essential in the control of cockroaches, as is the reduction of access to food and water. Food should be kept in airtight storage jars and any crumbs or waste should be cleared up straight away. The same applies to household refuse-bins with snap on lids will go a long way in controlling other pests such as ants and flies. Cockroaches can survive longer on just water as opposed to just food so reducing supplies to water is essential in controllingcock roach populations. Fix any leaks and sweating pipes, provide ventilation to moist areas, mop up any spillage's, do not leave washing up soaking overnight and empty any pet bowls over night.

The next step is to start to reduce potential harbourage in the areas suggested by the traps as being the most infested. Removing any clutter where cockroaches might live i.e. loose wallpaper, and broken tiles, cookery books and loose papers are a also a perfect haven. Any holes, cracks or crevices must be caulked, painted or sealed shut bearing in mind that the first instar of the young German cockroach can fit in a gap of less than 1mm. Before starting, these areas should be washed to eliminate any eggs, food material or waste that has accumulated. Any furniture suspected of harbouring cockroaches can be steam cleaned if appropriate, a pest control company in southern California regularly steam-cleans rubbish chutes in blocks of flats to clear cockroaches populations. Vacuuming regularly, especially in out of the way areas can suck up cockroaches, their eggs and the material they feed on. The dust in the bag should clog up the breathing apparatus of any cockroaches but to make sure, seal the dust bag in an sealed plastic bag.

If the cockroach problem is in a block of flats or offices then screening the many ducts and vents that interlink the building is essential. Remove existing grillwork and place aluminium screening behind it, making sure to caulk around the edge. If the above methods are followed then at least one flat or office should have a much reduced or cockroach free environment.

Chemical Control
If the above methods have been followed and there is still a problem then chemical control methods may be needed. It must be stressed that this should not replace the above physical methods but be used in conjunction with. Products available on the market come in surface sprays, space sprays and insecticidal baits. Surface sprays are applied to a particular area and generally need reapplication throughout the developmental period of the particular species. Space sprays tend to be used on a regular basis until the infestation is under control and to flush cockroaches out of their harbourages and onto an insecticide that is placed around the perimeter of the room. Baits have the advantage of being safer for pets and children and only need to be placed near a particular harbourage.(4)

Of the 37 active ingredients currently registered for use in the UK nine are organophosphates, four are carbamates and one is the persistent organochlorine insecticide lindane. Lindane is currently under review by the European Commission with a new report recommending suspension because of severe health and environmental data gaps (see PN 43 p3). The organophosphate diazinon and the carbamate carbaryl along with 8 other anticholinesterase compounds have had their approvals revoked by the Pesticide Safety Directorate because of lack of support by approval holders. Since the 20th April 1999 stocks in the UK are no longer allowed to be placed on the market by approval holders with others given two years to use up or sell on any stocks. It is strange that the manufacturers did not support these actives, could it be that phase III of the review-the submission of comprehensive safety data would be far to testing?(5)

For cockroach control one of the most effective and oldest insecticides is boric acid. It lasts for the life of the building if the powder is kept dry and cockroaches have not shown resistance to it like they have some other insecticides. It is one of the least toxic chemicals to humans and pets, however, boric acid is rarely used by pest control operators unless specifically asked to do so by the customer. The reason for this may be that it is applied as a dust which can be messy and take more time than liquid and aerosol formulations. Also boric acid can take between 5 to 10 days to take effect which is intolerable to some customers.

Other active ingredients that are generally less toxic to humans and pets are:

* Pyrethrins, contact poisons that penetrate the nervous system making the cockroach unable to move.
* Insect growth regulators (IGRs) which act by preventing a particular stage of development for example, sexual maturity therefore stopping reproduction. IGRs generally only control an existing population, if the non-chemical control methods mentioned above are not applied then a new cockroach population may soon enter the premises.(6)

Table 1. Concerns about cockroach treatments used in the UK (7,8)
Alpha cypermethrin (SP) endocrine disruptor, toxic to bees
Azamethiphos (OP) cholinesterase inhibitor, highly toxic to fish and birds, toxic to bees
Bendiocarb (C) cholinesterase inhibitor, fairly toxic to fish, toxic to bees
Bioallethrin & d-allethrin (SP) endocrine disruptor, highly toxic to fish
Bioresmethrin (SP)   endocrine disruptor, highly toxic to fish and bees, toxic to aquatic invertebrates
Boric acid (I)  
Carbaryl (C)   suspected endocrine disruptor, possible human carcinogen, cholinesterase inhibitor, toxic to bees
Chlorpyrifos (OP) cholinesterase inhibitor, toxic to fish, toxic to bees
Chlorpyrifos methyl (OP) cholinesterase inhibitor, toxic to fish, toxic to bees
Cypermethrin (SP)   endocrine disruptor, slight eye and skin irritant, possible skin sensitizer, highly toxic to fish, bees and aquatic invertebrates
Diazinon (OP) cholinesterase inhibitor, endocrine disruptor, mild eye and skin irritant, highly toxic to bees, toxic to birds
Dichlorvos (OP) suspected endocrine disruptor, cholinesterase inhibitor, possible human carcinogen, mild eye and skin irritant, moderately toxic to birds, highly toxic to bees and fish
Dimethoate (OP) endocrine disruptor, cholinesterase inhibitor, toxic to bees, phytotoxic to some species
D-Phenothrin (SP)   endocrine disruptor, toxic to fish & bees
Fenitrothion (OP) suspected endocrine disruptor, cholinesterase inhibitor, toxic to bees
Fenoxycarb (C) cholinesterase inhibitor, probable human carcinogen
Fipronil (PP) mild eye irritant
Flufenoxuron (BZ)  
Hydramethylnon   possible human carcinogen, reversible eye irritant, toxic to fish
Hydroprene & s-hydroprene (JHM)   mild eye irritant, bee larvae sensitive
Iodofenphos (OP)   cholinesterase inhibitor
Lambda cyhalothrin (SP) endocrine disruptor, mild eye irritant, highly toxic to bees and fish
Lindane (OC) endocrine disruptor, evidence of chronic disease, carcinogenicity and mutagenicity, very toxic orally, skin, eye and respiratory tract irritant
Methoprene (JHM) mild eye irritant, bee larvae sensitive
Permethrin (SP)   suspected endocrine disruptor, mild skin and eye irritant, skin sensitizer, toxic to aquatic invertebrates and bee, highly toxic to fish
Pirimiphos-methyl (OP) cholinesterase inhibitor, mild eye and skin irritant, toxic to bees and fish
Propoxur (C) cholinesterase inhibitor, probable human carcinogen, fetotoxic, very toxic orally, mild skin irritant, highly toxic to bees, phytotoxic to some species
Pyrethrins & pyrethrum extract (B)   mild skin and eye irritant, highly toxic to fish, toxic to bees
Piriproxyfen (JHM)  
Resmethrin (SP) endocrine disruptor, toxic to fish, toxic to bees, toxic to aquatic inveterbrates
S-bioallethrin (SP)  endocrine disruptor, toxic to fish
Tetramethrin (SP)  endocrine disruptor, toxic to fish, toxic to bees
Other actives that we have no information on are alkyltrimethyl-ammonium chloride and benzalkonium chloride, they are both quartenary ammonium compounds (QUATS) used in a great variety of household products. They are essentially fungicides used as in-can preservatives.
B = botanical, BZ = benzoylurea, CA = carbamates, I = inorganic, JHM = juvenile hormone mimic, OC = organochlorine, OP = organophosphates, PP = phenyl pyrazole, SP = synthetic pyrethroid

Cockroaches will eventually develop resistance to most pesticides. Chemical control will only work short term if changes in food hygiene and habitat modification are not made. There are health concerns over lindane, carbamates and organophosphates, with more than 33% of all callers to the Pesticides Trust [now PAN UK] Pesticide Exposure Support Line regarding these chemicals. For small cockroach populations the non chemical control methods described should keep the population down to a tolerable level.

The main source for this article was:
Common Sense Pest Control: Least-toxic solutions for your home, garden, pets and community, Olkowski, W., Daar, S. and Olkowski, H., Taunton Press, 1991, 216-228.

Other sources were:
1. Urban Entomology: Insect and mite pests in the human environment, Robinson, W.H., Chapman & Hall, 1996, 131-164.
2. Victor Roach Pheromone Trap is produced by Woodstream Corporation, 69 N Locust St., Lititz, PA 17543, US,
3. The IPM Practitioner, Volume XX, No. 5/6, 1998, 1-7.
4. Insect Pest Factfile, Biology and control. AgrEvo UK Ltd, 1998, 29pp.
5. Pesticides Safety Directorate News Update, 14th April 1999, ref: AAHL/8/99.
6. The Daily Hazard, NO. 44 September 1994, page 4.
7. Pesticides Trust [now PAN UK] Active Ingredient Database, 1999.
8. List of active ingredients that have been approved for use against cockroaches, provided by the Health and Safety Executive 13/05/99.

[This article first appeared in Pesticides News No.44, June 1999, p18-19]

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