The Bug Busters!

All you need to know about natural pest control using predators.
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 pest?

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 professionals.

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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