Wasp control - least toxic options

Are chemical control methods safe enough to use in the household environment and is treatment necessary at all with the use of safer alternatives? As part of an ongoing series in Pesticides News, this report aims to help reduce hazards from the home environment.

It is often forgotten that wasps are beneficial insects, who eat harmful insects and their larvae and like bees, pollinate flowers in their search for nectar. There are eleven species of wasp in Europe with the Vespula germanica and Vespula vulgaris species being most common. Nests tend to be found underground, in hollow trees or in the eaves, attics and inside wall cavities of buildings. Wasps are social insects and when found in urban areas colonies can come into contact with people. The report of an 'Invasion of the Eurowasp', the dolichovespula medium from the continent, with its greater size and more painful sting(1) has prompted this fact sheet which hopes to reduce the number of painful encounters people have with wasps and reduce the need for pesticide use by providing a greater understanding of the wasp and its habitat.

Biology
The queen who spends the winter hibernating, initiates her nest in early spring. She feeds on captured prey and nectar before laying her first eggs in cells constructed out of chewed wood and plant debris. The queen feeds the larvae until the first brood of workers hatch, these workers take on the responsibility of looking after future larvae, they gather food and carry on constructing the nest while the queen continues to lay eggs(2).
    The colony expands throughout the summer with the maximum number of workers occurring about three months after initiation of the nest. Reproductive males and new queens are the last to hatch and leave the nest to mate, the males die soon after, while the queens look for a protected site to hibernate over winter. At this time the workers change their foraging habits from looking for food and materials for the nest, to nuisance scavengers, finding sweet substances to replace a similar sweet liquid which was secreted from the larvae(3). This is the time when most people come into contact with wasps. It is worth noting however that with the onset of colder weather the workers die off and the nest decomposes never to be reused again.

Natural wasp control
Most pests get into the home through gaps in the exterior of the building such as cracks around door and window frames or through unscreened vents. A small amount of building maintenance will help to keep the nests of wasps and other pests on the outside.
    To limit exposure to wasps outside, supplies of potential food sources be must cut off. In the early months of the summer, workers are attracted to protein foods found at picnic areas, rubbish sites and pet food dishes, however they are much more of a nuisance when attracted to sweet food and drinks at the end of their life cycle. Physical controls include keeping pet food bowls inside, using lids and straws on drinks, using well fitting lids on bins and cleaning rubbish areas regularly(4).
    Non-chemical traps can be bought that attract wasps away from sensitive areas, if deployed early and in the correct areas, wasp populations can be reduced to acceptable levels. In areas where food is prepared and sold, traps in conjunction with electrical fly killers are recommended.

Nest destruction can be achieved if the nest is easily accessible.
Aerial nests
Place a large plastic bag over the entire nest and knock the nest into the bag, sealing tightly. Wasps cannot survive extreme temperatures so freezing or leaving the airtight bag in the direct sun on a hot day will kill them, alternatively drowning them will do the same job.
Ground nests
Eliminate by placing a clear bowl over the nest entrance, pushing the edges into the earth and sealing any gaps. The wasps do not dig a new way out and starve within a few weeks.
Indoor cavity and underground nests
In the US, wasps can be vacuumed out (using specially adapted vacuum cleaners) by professionals and sold to pharmaceutical companies who collect the venom for immunotherapy. The nests are then destroyed. This type of non-chemical service is unavailable in the UK so these types of nest are best left for the professionals to deal with.(5)

The best time for dealing with wasps is at night-time when it is cooler and most of the workers have finished their foraging and are back in the nest. In dealing with nest removal/destruction it is important that protective clothing be worn at all times, covering hands and face, making sure there are no exposed parts of the body. Wasps should never be disturbed when children or allergic people are nearby and it is advisable to step lightly, filtering any flashlights, as vibrations and yellow or white lights attract wasps.

Chemical Control
If the level of wasp activity is such that it is unbearable, then your local authority or a pest control company (British Pest Control Association, (BCPA) recognised) should be called in to deal with the problem. They can use a variety of insecticidal dusts or liquid formulations and you must ask what they use before agreeing to any work being done (see table 1). The Pest Manual recommends the use of carbamate or organophosphate active ingredients over pyrethroid based products(6). This is of concern as both classes of pesticide are acetocholinesterase inhibitors designed to damage nerve function. Acute effects may include: behavioural disturbances, headache, dizziness, abdominal cramps and diarrhea. Chronic effects in extreme cases may include damage to the liver and kidney, sperm abnormalities, cancer, genetic mutation and fetotoxicity. Soap are least toxic of those mentioned in the table followed by synthetic pyrethroids and pyrethrins.(7)

Avoid being stung
Wasps do not sting unless they have reason, so avoid swatting or squashing as a chemical is released which signals other wasps to attack. In areas where there is likely to be wasp activity, i.e. picnics in late summer, avoid wearing bright colours, perfumes and other strong scents, do not walk around bear-footed, and take care handling wet material as wasps are known to drink moisture from towels and clothes etc.(8)
    If stung, the wound should be washed with soap and water which helps remove some of the venom and treated with an anti-sting product or antihistamine cream which can reduce the pain and spread of the venom. If the sting is in the throat or mouth, or if an allergic reaction occurs seek medical attention immediately.

Clinical effects that may occur following a wasp sting(9)
Local reactions
Normal reactions to a sting include immediate pain and redness, irritation, itching and swelling localised at the site of the injury. If the sting is on the tongue or in the mouth the local swelling may potentially cause respiratory distress.
Toxic reactions
These normally occur with multiple stings. The clinical effects include local reactions as above, with vomiting, diarrhoea, headache, hpyotension, fever and very rarely transient loss of consciousness, convulsions and renal failure have been reported.
Allergic reactions
In certain individuals a single sting may produce serious, potentially fatal, anaphylactic reactions usually within 30 minutes. Clinical effects include rashes, itching, nausea, vomiting, diarrhoea, abdominal cramps, dizziness and headache. Hypotension, palpitations, bronchospasm and collapse may occur in severe cases.

Once again seek medical attention if you suffer a toxic or allergic reaction.

Comment
With good building maintenance, limiting access to food and the use of safe alternatives such as trapping, the amount of wasp activity around the house and garden should be kept to a manageable level. If pesticides must be used, then make sure a recognised contractor or your Local Authority carries out the work, using the least toxic substance available to protect your health and the environment.

1. Daily Mail, 23 July 1998, p28.
2. Common Sense Pest Control: Least-toxic solutions for your home, garden, pets and community, Olkowski, W., Daar, S. and Olkowski, H., Taunton Press, 1991, 650-661.
3. Urban Entomology: Insect and mite pests in the human environment, Robinson, W.H., Chapman & Hall, 1996, 321-343.
4. Quick Solutions, BZZZZ, New York Coalition for Alternatives to Pesticides, October 1997, 15pp.
5. Solving Yellowjacket Problems, Lind, P., Journal of Pesticide Reform, Spring 1998, 22-23.
6. ADAS Pest Manual
7. Op. cit. 4
8. Op. cit. 2
9. Management of venomous, bites and stings, Emergency Nurse, March 1998, Vol 15, No.10, 12-16.
10. Pesticides Trust [now PAN UK] Active Ingredient Database, 1998.
11. Pesticides 1998: Your guide to approved pesticides, UK Health & Safety Executive, 1998, 571pp

[This is an extended briefing of an article that first appeared in Pesticides News No. 41, September 1998, p19]