The Bug Busters!
All you need to know about natural pest control
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Tony King, 34 Keats Avenue, Romford, Essex
Chamaerops No. 7, published online 23-10-2002
Left: Hunter (Phytoseiulus persimilis)...
Right: ...and hunted (Tetranychus urticae - Red Spider Mite).
If we are all honest, it's not just the plants that
we have thriving in our collections. Often, the objects of our desire
are home to a multitude of sucking and biting creatures intent on
destroying our most prized possessions. Isn't it always THE most
desirable or rarest specimen that acts as a magnet for every passing
Like me, you probably reach for a poisonous cocktail
mixed with water and spray with abandon, as soon as an infestation
is spotted. Usually a very effective method too, but not without
problems. Spraying has to be undertaken regularly - quite laborious
if you have many plants, and indeed some groups of plants are themselves
damaged by the chosen chemical control. This is of course not counting
the toxic effects of the sprays on the human users! An increasing
problem too is the resistance being built up by the pests to our
most successful potions, which are becoming less and less effective
as time goes by though they are still able to indiscriminately kill
any beneficial creatures caught up in the spray applications. The
EEC is also actively reducing the substances available to amateur
gardeners allowing the more potent substances to be used only by
There is however, another way: an increasingly proven
way of combating our damaging enemies using 'beneficial' creatures
Natural Pest Control using predatory insects. After all, in the
wild there isn't anybody to spray a plant that becomes host to an
outbreak of a pest. A natural enemy has to be relied upon to keep
things in check. These predators have now been successfully identified
and are freely available to the amateur.
Despatched from the breeder as either eggs or young,
the predators should be introduced as early in the season as possible,
as control can take some time to work effectively. Once established
and reproducing, the natural enemies can continue throughout the
season keeping pest numbers down to acceptable levels. In a modest
sized collection it will not normally be necessary to reintroduce
the predator during the season, unless a very bad infestation occurs.
The drawbacks, well, you cannot really use insecticides since they
do not discriminate between friend and foe. For emergency SPOT treatment,
however, sprays containing pyrethrins, Rotenone or primicarb are
the least damaging. Fungicides, with the exception of Nenelate,
are safe if used with care. The other snag is temperatures below
12°C (except for short periods), which cause the predators to
become inactive and indeed can result in their death.
So, who are our friends and foes?
Well, my 'public enemy number one', and I'm sure
many readers will agree, is Red Spider Mite. The familiar yellowing
of a leaf as they suck the lifeblood from a treasured plant is all
too familiar. Before you know it, the plant is covered in the telltale
cobwebs and looking very sickly indeed. Encouraged by a dry atmosphere,
they breed at a remarkable rate and are especially difficult to
control by chemical means. Surprisingly, it is to another mite that
we turn for assistance, PHYTOSELULUS PERSIMILIS to be precise!
This is a little larger than its prey and orange
in colour, so is visible to the naked eye. Laying around 50 eggs
over a three-week period, during which time it will consume around
7 spider mites or 20 of their eggs each day, this is an effective
predator. With warm temperatures it is very active and can control
an infestation in around three weeks, particularly if humidity can
also be maintained. The predator likes the warm moist environment
whilst the spider mite does not, so this helps for speedy control.
During the summer, the Phytoseiulus can be used outdoors, though
due to unpredictable weather conditions, results can be variable.
Despatched on bean leaves, which should be cut into
pieces on arrival and distributed around the infected plants, the
predators will make off in search of food - the spider mites!
Second only to the Red Spider as a bad pest must
be the whitefly and if these trouble you then ENCARSIA FORMOSA is
what you need! If you do have a whitefly problem you will be only
too aware that they can be difficult to control. The adult flies
feed on the underside of the leaves and can lay around 100 eggs
at a rate of 5 a day. Hatching in just one week, the larvae move
to voraciously commence feeding on new plant growth as well as untouched
leaves, maturing into free flying adults in 3-4 weeks. Not only
are these creatures depriving your plants of vital nutrients, they
also excrete 'honeydew', a waste substance on which Sooty Moulds
can then grow, creating potential for more damage.
Unlike spider mites, which hibernate in winter,
whiteflies can continue to breed all year round even surviving freezing
conditions. At 22°C, their life cycle is complete in 4 weeks;
at 12°C it takes 8-9 weeks.
The control agent, Encarsia formosa, is a minute
black and yellow wasp. Each adult wasp, some 1.5mm long, lives for
around 3 weeks but during this time lays 50 or more eggs, each hatches
inside a whitefly egg (or scale) and the Encarsia larvae feed off
the developing whitefly. After 10-12 days a parasitized scale turns
black indicating the whitefly has been consumed and a further 10-12
days later, the adult wasp emerges to continue the cycle. At temperatures
below 190c, development slows and at 15°C each stage will take
3 weeks. It is essential therefore to maintain suitable temperatures
and introduce Encarsia before the whiteflies become too numerous,
as large numbers excrete so much honeydew that the wasp is hampered
in its task of eradication.
Those of us who number succulent plants among our
collections will especially be familiar, no doubt, with mealy bugs.
Difficult again to kill by chemical means these white fluffy pests
live beneath their own waxy coating of powdery 'meal' that gives
them their name and keeps our sprays from penetrating.
Apart from its sap sucking damage, honeydew is again
secreted which encourages the growth of harmful moulds. A predatory
ladybird, this time comes to the rescue - CRYPTOLAEMUS. Where temperatures
can be maintained above 18°C good control can be established.
Adult beetles are best released in spring when daytime temperatures
have reached the correct level. The predator can then actively search
for mealy bug colonies.
Once successfully established, Cryptolaemus will
reduce pest populations to a low level over 2-3 months. After this
period once pest numbers have been reduced, small introductions
of the ladybird will be necessary to maintain control.
Although I have concentrated on the three main problem
pests and their respective controls, predators are available to
do battle with many other troublesome pests. Aphids, thrips, etc
all have an effective control predator. The hunter will never eat
all its prey though hopefully the hunted will never build up to
plague proportions. I have seen these creatures used very effectively
in many collections and you must agree that the fewer poisonous
chemicals we release into the environment, the better. So let Mother
Nature have a go. You may be very surprised by the result.
Thanks to Natural Pest Control for supplying the
information used in compiling this article. They are to be found
at Yapton Road, Barnham, Bognor Regis, West Sussex, P022 OBQ. Tel
0243-553250, and can supply all of the listed predators and others.
Thanks also to Koppert U.K. Ltd for the kind loan of the photographs.
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