with a good memory for places
An alternative approach to wasp control
Dr. Manfred Fuchs, Koblenz, Germany
*(All seasonal indications are related to Europe)*
early spring with no major cold spells, followed by a long hot
and dry summer, numerous large colonies of wasps have to be
expected. The result is a corresponding increase in the nuisance
they cause, and in the health risk they pose: not only with
their stings but also - though less visibly - through their
contamination of foodstuffs and beverages. This is because they
are carriers of pathogenic micro-organisms.
not be such a big problem if these pests only went for foodstuffs
that contain sugar - a substance that inhibits the breeding
of germs. Wasps, however are not mainly attracted to sweet things.
The attentive observer will notice that protein-containing foods
such as meat and sausage are also prime target for the wasp's
air-raids. This is because wasp larvae have a very high protein
requirement which is mainly met by wasps attacking other insects,
manure heaps, faeces, and decomposing animal cadavers are highly
suitable depositories for flies' eggs, they are major attraction
for wasps, which duly pick up pathogenic germs. Back in 1952/53
and in 1960 Döhring (1) found wasps on rubbish dumps and in
pigsties almost 100 % contaminated with faecal germs.
who has seen a dense swarm of wasps going to work on a not yet
too severely decomposed animal cadaver is aware of the very
real threat this can subsequently pose to human hygiene. The
insects often infect their stings with puss pathogens which
can later be injected into human skin together with the wasp's
cases, the body's reaction to the sting is particularly severe.
Swelling occurs around the area stung, followed by painful inflammation
and festering that may even lead to blood poisoning.
central European wasp varieties, three are often to be found
in the vicinity of people: the common wasp (Paravespula vulgaris)
the German wasp (Paravespula germanica), and the hornet (Vespa
crabro). The hornet is the biggest wasp and the one which is
most likely to sting. With all varieties of social wasps, it
is always the female workers and queen that sting. The males,
which are to be found with the young queens or with the autumn
queens in the months from August to October do not have a sting.
As is well
known, the nests consists of a paperlike mass. They are built
and constantly repaired and upgraded by the female insects using
wood meal and saliva - in the spring the queen does the work
alone after having survived the winter. If weathered wood is
used, nests have a largely greyish colour. A nest covering of
stripy appearance indicates the use of various types of wood.
No matter how large a nest is , it was always built during a
single breeding season and will never be used a second time.
Only the fertilized young queens survive the winter and each
build a new nest in the spring - usually from late April onwards.
Initially the queen also searches for food and handles the business
of brooding on her own, until the first female workers are hatched
by mid June. In the weeks and months that follow, the wasp colony
undergoes massive expansion. The highest population count is
reached in the second half of August, and numbers gradually
begin to dwindle only from late September onwards. The population
then declines sharply, and by mid-November all the female workers,
the nest's founder (the old queen) and the males have died out.
The wasp year begins anew the following spring when the young
queens restart the cycle.
wasp presence is at it height in the months from August to October.
A female worker flying out of the nest has one of three reasons
for doing so: she is looking for nest-building material, water
or food. Once she has found a bountiful source, she will return
there time and again. Her task is made easier by an excellent
memory for places and by an ability to gauge where the sun is
in the sky even in cloudy weather, taking into account positional
changes over the course of the day in relation to the food source.
This is a capability which wasps have in common with bees, which
have a higher level of organisation. Unlike bees, however, they
never create stocks of food.
source of nourishment for all wasps and hornets, particular
the brood, is provided by other insects and spiders. As high-protein
food quickly spoils, it is not possible to keep stocks. That
is the main reason why colonies of wasps die out in the autumn.
climes, wasp species which are also indigenous in central Europe,
do build nests for use over several years. These may reach astounding
sizes. There are basically three ways of combating wasps:
the queens in the spring or autumn - this prevents wasps' nests
from being built in the first place.
Eliminating the female workers in the summer - this has the
effect of weakening the population: in the best possible scenario,
the brood dies out. Eliminating the female workers in late summer
and autumn - essentially this merely reduces the level of nuisance.
3. Mechanical destruction of the nest or rapid destruction of
the population using insecticides.
procedure is the most elegant solution. The problem is that
the queens do not make themselves noticeable in the spring,
and catching them in traps is the exception rather than the
rule. The autumnal success rate is a lot higher. As the female
workers die out, the young queens have to look for food themselves.
They can then often be caught in jars containing bait liquids
(sour fruit juices, malt beer, slightly sugared vinegar - in
summer months, do not use sugar-, honey- or syrup-water, as
this will attract bees), if these are set as traps in late summer.
The second approach is steeped in tradition, and will serve
at best to reduce the wasp nuisance if conventional traps are
hung up in the vicinity of the nest. What is more, will give
the person concerned the satisfaction of his or her having "paid
back" the wasps for their unwanted attentions.
nest accommodating thousands of female workers will not be appreciable
weakened by a few hundred specimens being caught.
a nest can be destroyed, however, it first has to be found.
Careful observation of the wasps' movements over an approximately
50 metre radius usually leads to the nest being successfully
located. The range over which wasps will usually search for
food is 50 to 250 metres from the nest, although wasps are capable
of flying far greater distances.
task of destroying the nest, sometimes using anaesthetic substances
such as laughing gas or carbon dioxide, is often performed by
fire brigades. The people doing the business are subject to
the most virulent attacks by the enraged wasps, and protective
clothing does not always prevent stings.
the sound of an attacking wasp differs markedly from the usual
flight sound and causes other wasps to likewise attack. Also,
the poison-secreting gland also produces an alarm-triggering
substance which the wasp hurls in droplets at the enemy, thus
leaving a marker that will tell other wasps to attack. This
substance is not identical to the wasp's poison.
about the job of removing a wasp's nest, the professional pest
controller will avoid endangering him- or herself or other people.
He or she will therefore do the job late in the evening or early
in the morning, when the outside temperature is as low as possible.
Most female workers are then in the nest. It should not be forgotten,
however, that a considerable number of wasps will spend the
night outside the nest, and that flight movements will not be
discontinued until the light is very weak and will resume as
soon as the morning light permits (1.5 lux). Hornets quite often
hunt at night when light conditions range between 0.2 and 0,03
are used, evenings and mornings are the best times. An aerosol
can (with locking valve) attached, if necessary, to the end
of a sufficiently long rod and held in the immediate vicinity
of the nest will do the trick. However, if the use of insecticide
is liable to cause problems (e.g. if the nest is to a kindergarten,
school, hospital or food-processing factory), a highly effective
alternative is to use UV-A-light flytrap reflectors featuring
adhesive trapping surfaces. Longwave light in the 365 nanometre
range attracts numerous flying insects because the sun is the
only natural source of this light, and when the insect picks
this light up either directly from the sun or as global radiation
from a cloudless sky, the message it receives is that there
is an unobstructed flight path ahead.
As is the
case with many insects, colour vision for wasps begins in the
longwave UV range, and the ultraviolet receptors in the wasp's
eye reach maximum absorption at precisely 365 nanometres. The
luring effect on a phototropically disposed wasp is therefore
particularly great. A wasp flying out of the nest is constantly
seeking an unimpeded flight path. It therefore takes the radiation
of a UV-A lamp to be bright daylight and flies directly towards
it, only to be trapped on the adhesive surface. Conversely,
a Wasp that is looking for food or wood and flies to a window
or to a dark piece of wood is photophobic. If it is forced to
fly away to escape danger or if it has found what is was looking
for, however, the mode switches over and it will once again
seek an unimpeded flight path. If the light trap is now the
brightest source of ultraviolet A-region light in the vicinity,
the wasp will head straight for it. The picture illustrates
the effectiveness of such trap (iGu® FANGREFLEKTOR®
FR 3003). Compared with units using a UV-A lamp surrounded by
a high -voltage grid, the adhesive foil offers a number of advantages:
it keeps a firm hold on the insect, whereas high-voltage bug
killers are liable to hurl the electrocuted insects out of the
device and possibly into foodstuffs (unhygienic); and the insect
may still be able to sting (dangerous) If they remain on the
grid, they will burn there, giving of a very unpleasant smell.
The trapping principle embodied by the adhesive surface is therefore
tests carried out in the Koblenz area (Germany) over recent
years have shown that the wasp nuisance in bakeries, on fruitstalls,
in cafes and in beer gardens can be appreciable reduced. The
direct elimination of female workers flying out of the nest
efficiently decimates a wasp colony. Within a few days, the
population collapses, provided the trap is well placed and the
adhesive foils are exchanged when full.
(1) Kemper, H.; Döhring, E. !1967: Die sozialen Faltenwespen
Mitteleuropas: published by Verlag Paul Parey, Berlin/Hamburg
(2) Edwards, R. (1980): Social wasps. Their biology and control.
The Rentokil Library, Rentokil Ltd., Felcourt, East Grinstead,
1980 ISBN 0 0906 564 018.
RD Dr. M. E. A. Fuchs, Zentrales Institut des Sanitätsdienstes
der Bundeswehr Koblenz (Central Institute of the German Armed
Forces' Medical Corps, Koblenz), Ernst Rodenwaldt Institut -
Control using light traps
How effective are modern devices?
as causing a nuisance with their stings (midges, wasps, stomoxyine
flies) or by their mere approach and skin contact /houseflies),
flying insects can directly transmit pathogenic micro-organisms
to humans and pets as well as to economically useful animals
and plants. The damage that can thereby arise may also occur
indirectly as a result of foodstuffs and articles of daily use
being infected with germs.
(musca domestica), the stable fly (musca stabulans) as well
as carrion- and faeces-visiting fleshflies (sarcophaga spec)
greenbottles (lucilia spec), phormiae and bluebottles (calliphora
spec.) are regarded as being particularly effective vectors
of pathogens With flies the transmission of pathogenic micro-organisms
is inevitable, every fly being able to carry up to five million
germs including the pathogens of such serious diseases as typhoid,
cholera, dysentery, polio, pneumonia and foot and mouth disease.
On a suitable substratum germs multiply very rapidly. Thus,
with the aid of a culture medium (blood agar), it can very easily
be demonstrated that a housefly, for example, leaves behind
its own bacterial trail.
in which a housefly goes about its food intake promotes the
transmission of micro-organisms in several ways:
1. By walking around on the surface of the food "facultatively
tactile" contamination takes place.
2. Houseflies, in common with other species of fly having a
proboscis, cannot take nourishment in the form of solids. The
proboscis secretes digestive fluids onto the food so as provide
liquefaction and accomplish partial extracorporeal digestion.
The resultant solution is then sucked in by dabbing.
representation of a housefly sucking in a liquefied
and pre-digested food particle by dabbing
simultaneously a dropping of faeces is excreted, releasing germs
from the fly's intestines. This mode of transmission is termed
"facultative excretory." If a foodstuff is moist and contains
protein, it is also used as an egg depositary. A housefly lays
a total of around 2'000 eggs. Given a suitable temperature the
maggots hatch out within a matter of hours.
the numbers of injurious flying insects has therefore always
been a major objective of human endeavour.
It is a
well known fact that insects will fly towards sources of light.
Anyone can observe this phenomenon on a summer's evening. Provided
they have a fundamentally phototropic disposition, nocturnally
active insects will fly towards any source of light, naked flame
(candles, oil and gas lamps) and electric light of any spectral
composition that can be perceived by the insect eye. Diurnal
flyers do not do this to the same extent. They are more strongly
attracted if the light source emits portions of long-wave A-region
ultraviolet light in the 365 nm range. While night flyers interpret
any visible light source as signifying an open flying space,
the day flyer - whose movements in any case take place in daylight
- requires a more specific signal indicative of open flying
space. Just such a signal is provided by long-wave ultraviolet
light, which as far as the insect is concerned can only emanate
from the sun or, as global radiation, from a cloudless sky.
Many winged insects have undergone specific evolutionary adaptation
to this type of signal: the ultraviolet-sensitive receptor in
the compound eye exhibits maximum absorption at 365 nm.
Knowledge of this phenomenon has been exploited for years in
the design of flytraps employing A-region ultraviolet light.
The source of light is provided by tube-type fluorescent lamps
with a rating of between 4 and 40 Watt. They emit a bluish-white
light which always contains a certain portion of light in the
365 nm radiation range.
If an insect's
behavioural circumstances are conducive to flight, this light
will exert a "luring" effect as it contains for the bug the
basic information that open flying space is available. With
this type of trap, however, no differentiation can be made between
so-called injurious, indifferent and useful species.
It is hardly
surprising, therefore, that the use of flytrap devices employing
this luring principle is banned in outdoor areas. And they will
remain restricted to indoor application. Their deployment is
appropriate and necessary in rooms where hygiene is of the essence,
e.g. in food production and processing operations, in all clean-room
areas in the chemical and pharmaceutical industry, in corresponding
research establishments and in hospitals; other areas of application
are animal accommodation (including for experimental animals)
and of course hotels and homes whenever flying insects become
tests which have been carried out here since 1974, the results
of which have been reported on several times (Fuchs 1975, Mainhart
1980, Fuchs 1992), it has been established that all traps become
more effective as the amount of A-region ultraviolet light increases.
An upper limit has not been detected to date. UV-reflective
surface areas behind the tube-type fluorescent lamp increase
the amount of UV-A light and thus enhance trapping performance.
orientation aids can be offered to the flying insect as it makes
its approach. For example, the trapping rate increases if the
housing of the particular device provides a stark contrast between
the light source and its background. Inter alia, the UVA-light-emitting
fluorescent tube with its 50 - 60 Hz flicker produces a "lighthouse"
effect. This is because the compound eyes of a flying insect
possess a much higher fusion frequency than, for example, the
human eye. Whereas for us a tube-type fluorescent lamp emits
light uniformly, to such an insect it appears to be constantly
switching on and off.
principles In conjunction with the luring effect of A-region
ultraviolet light two trapping/bug-kill principles are applied:
1. Arranged in the immediate vicinity of the ultraviolet-light-emitting
tube(s) is a high-voltage grid or a grid/plate combination designed
to electrocute the insect as it lands by means of a short-circuit
spark. For safety reasons the amperage is low (up to 15 mA),
the voltage being mostly several thousand V.
large-size devices of this type turn in an extraordinarily high
trapping performance but do not always meet hygiene requirements.
In the most favourable case the insect is killed immediately,
falls vertically into a catching bowl attached to the bottom
of the unit and is thus initially hygienically removed. However,
a draught may blow dead insects or insect particles out of the
catching bowl. After all, a housefly weighs only around a milligram.
however, the insect is torn to pieces by the short-circuit spark.
Particles are hurled out of the device and contaminate surfaces
and various objects - depending on the use to which the room
is put - and in the worst case foodstuffs are affected. The
bottom line is non-compliance with statutory hygiene requirements.
it appears otherwise, the least objectionable scenario from
the hygienic point of view is when an insect, mostly a large
one such as a wasp or a bluebottle, remains attached to the
electrical grid, drying out and burning in the electric arc.
This is because all germs are thereby destroyed. Other disadvantages
arise, however. During the burning process the high voltage
system is down and further insects coming into land are not
destroyed. There is an unpleasant smell of burning. The vapours
blacken the high-voltage grid, reducing the level of ultraviolet
reflection and hence the luring effect. - In rooms whose atmosphere
entails the risk of explosion, the use of electrical traps is
out of the question.
further fly-kill principle which has only been used in conjunction
with ultraviolet-light traps over the past few years involves
the use of adhesive-coated surfaces positioned in a semi-circular
arrangement behind or next to the UV-A lamps. The transparent
adhesive substance, applied to thin cardboard, is exposed by
peeling off a protective foil. It reflects A-region ultraviolet
light, remains sticky for a very long time and traps insects
up to the size of a hornet securely and hygienically. (Normal
adhesives quickly lose their stickiness when subjected to irradiation
by A-region ultraviolet light). From the aspect of hygiene,
therefore, this trapping principle is definitely the preferred
the smallest devices currently available on the world market
employing this combination without an electric grid is called
the FANGREFLEKTOR iGu FR 3003 from iGu Transtrade Ltd., Christchurch,
New Zealand. When placed in a 40m3 room containing 200 houseflies,
this unit achieves a trapping rate of 100% in just 4 hours,
at an LT50 (= time after which 50% of the flies are caught)
of 43 minutes. In the case of high-voltage-grid-type devices,
this level of performance is only achieved by larger-size and
appreciably more expensive industrial units. The iGu flytrap
reflector's easy-to-change foil has a surface area of 630 cm²;
the U-shaped tubular lamp emitting A-region ultraviolet light
is rated at 10 Watt.
biggest units of this type currently available are iGu's FR
8008-series flytrap reflectors. The FR 8008 features two foil
holders with a total surface area of 4,800 cm² and operates
with two 60-cm long 20-Watt tubes. Two further versions are
offered, one featuring two shielded 40-Watt UV-A fluorescent
tubes and the other equipped with two explosion-proof lamps
each rated at 20 Watt.
The FR 8008
catches 200 houseflies in the same room in one hour and thirty
minutes, with the LT50 mark being reached in just a quarter
of an hour.
It is interesting
to note that, related to the size of the traps, the trapping
times evidently do not depend on the number of flies used in
are 20 flies in the room, these are not eliminated in a shorter
time than 200 flies. In a room of the same size the insects'
inclination to fly increases with the amount of ultraviolet
a higher amount of ultraviolet light also increases the luring
distance. Even in homogenous fly populations of musca domestica,
however, the intention to seek open flying space is evidently
statistically congruent. From this it must be concluded that
in rooms where hygiene is of the essence only large traps should
be used, even if the occurrence of flies is low.
held view that where the incidence of pests is low a small-size
trap will suffice is erroneous. Rather, before recommending
a trap size (= specification of trap capacity) the question
that has to be asked is "how many flies or other winged insects
is the user prepared to tolerate in a room and for how long?"