Biological Pest Management

Biological Pest Management (BPM) at Burt’s Greenhouses

“When we kill off the natural enemies of a pest. We inherit their work!” – C.B Huffaker

Burt’s Greenhouses uses Biological Pest Management

When we first started in the greenhouse business, using insecticides was the only solution to pest problems in the greenhouse. The more training we got in the use of insecticides, the more we wanted to stop using them, both for our health and for yours. The government rates all chemicals based on their danger to human health. The chemicals that are consistently at the top of the list are the insecticides.

How Does This Work?

In nature, life will generally achieve a balance of some kind. This is not always to the liking of we humans. The greenhouse environment is not a natural one. In the wild, many different plants and critters interact, benefiting each other and, yes, eating each other. In the greenhouse, we create an artificial environment in order to start growing plants in the middle of winter. In the relatively closed environment of the winter greenhouse, great care must be exercised in order to defend against the ravages that can be inflicted by outbreaks of uncontrolled harmful pests. The problem with resorting to chemicals whenever a “bug” is seen is that many insects are actually beneficial to gardeners but the insecticides are generally bad for everyone. If, instead of trying to kill off all the little critters in the greenhouse, we make use of the beneficial insects to control the pests, we can virtually eliminate our need for chemical insecticides.

In short, we have chosen to use bugs to control bugs. We use a number of insects that feed on or parasitise the major pests that affect our crops (see pages 5 and 6). We also use tiny nematodes, which are not insects, which feed on the larvae of thrip, fungus gnats and shore-flies. The only insecticide we use is insecticidal soap. All cuttings that come from other greenhouses into ours are dipped in insecticidal soap so that we can have a relatively pest-free start to our growing season.

Are We Unique?

We certainly are. BGH was the first major Annual/Perennial greenhouse operation in Eastern Ontario using Biological Pest Management.Operations such as ours are still rare. In Canada, a great deal of biological control is being used in the vegetable greenhouse industry, but for flower growers it is a far different story. It takes a whole new knowledge set to monitor all of the pests and to know when to introduce the appropriate beneficial insects. Cookbook remedies that would work with chemicals do not work here. If the system is to succeed, you must never use insecticides or you will kill the good guys as well as the bad.

BPM Is Best Defined as …

Biological Control is defined as the reduction of pest populations by natural enemies and typically involves an active human role. Natural enemies of insect pests, also known as biological control agents, include predators, parasitoids, and pathogens. Predators, such as ladybugs and lacewings, are mainly free-living species that consume a large number of prey during their lifetime. Parasitoids are species whose immature stage develops on or within a single insect host, ultimately killing the host. Most have a very narrow host range. Many species of wasps and some flies are parasitoids. Pathogens are disease-causing organisms including bacteria, fungi, and viruses. They kill or debilitate their host and are relatively specific to certain insect groups. There are three basic types of biological control strategies; conservation, classical biological control, and augmentation. These are discussed in more detail below.


The conservation of natural enemies is probably the most important and readily available biological control practice available to homeowners and gardeners. Natural enemies occur in all areas, from the backyard garden to the commercial field. They are adapted to the local environment and to the target pest, and their conservation is generally simple and cost-effective. Lacewings, lady beetles, hover fly larvae, and parasitized aphid mummies are almost always present in aphid colonies. Fungus-infected adult flies are often common following periods of high humidity. These naturally occurring biological controls are often susceptible to the same pesticides used to target their hosts. Preventing the accidental eradication of natural enemies is termed simple conservation.

Classical Biological Control

Classical biological control is the introduction of natural enemies to a new locale where they did not originate or do not occur naturally. This is usually done by government authorities. In many instances the complex of natural enemies associated with an insect pest may be inadequate. This is especially evident when an insect pest is accidentally introduced into a new geographic area without its associated natural enemies. Examples of introduced vegetable pests include the European corn borer, one of the most destructive insects in North America. To obtain the needed natural enemies, scientists turned to classical biological control. This is the practice of importing, and releasing for establishment, natural enemies to control an introduced (exotic) pest, although it is also practiced against native insect pests. The first step in the process is to determine the origin of the introduced pest and then collect appropriate natural enemies associated with the pest or closely related species. The natural enemy is then passed through a rigorous quarantine process, to ensure that no unwanted organisms (such as hyperparasitoids) are introduced, then they are mass produced and released. Follow-up studies are conducted to determine if the natural enemy becomes successfully established at the site of release, and to assess the long-term benefit of its presence.


This third type of biological control involves the supplemental release of natural enemies. Relatively few natural enemies may be released at a critical time of the season (inoculative release) or literally millions may be released (inundative release). Additionally, the cropping system may be modified to favor or augment the natural enemies. This latter practice is frequently referred to as habitat manipulation.

An example of inoculative release occurs in greenhouse production of several crops. Periodic releases of the parasitoid, Encarsia formosa, are used to control greenhouse whitefly, and the predaceous mite, Phytoseiulus persimilis, is used for control of the two-spotted spider mite.

Ladybugs, lacewings, or parasitoids such as Trichogramma are frequently released in large numbers (inundative release). Recommended release rates for Trichogramma in vegetable or field crops range from 5,000 to 200,000 per acre per week depending on level of pest infestation. Similarly, entomopathogenic nematodes are released at rates of millions and even billions per acre for control of certain soil-dwelling insect pests.

Habitat or environmental manipulation is another form of augmentation. This tactic involves altering the cropping system to augment or enhance the effectiveness of a natural enemy. Many adult parasitoids and predators benefit from sources of nectar and the protection provided by refuges such as hedgerows, cover crops, and weedy borders. Also, the provisioning of natural shelters in the form of wooden caskets, boxes or (turnaround) flowerpots is a form of this. For example, the stimulation of the natural predator Dermaptera is done in gardens by hanging up turnaround flowerpots with straw or wood wool.

Mixed plantings and the provision of flowering borders can increase the diversity of habitats and provide shelter and alternative food sources. They are easily incorporated into home gardens and even small-scale commercial plantings, but are more difficult to accommodate in large-scale crop production. There may also be some conflict with pest control for the large producer because of the difficulty of targeting the pest species and the use of refuges by the pest insects as well as natural enemies.

Examples of habitat manipulation include growing flowering plants (pollen and nectar sources) near crops to attract and maintain populations of natural enemies. For example, hover fly adults can be attracted to umbelliferous plants in bloom.

Examples of Predators

Ladybugs, and in particular their larvae which are active between May and July in the northern hemisphere, are voracious predators of aphids such as greenfly and blackfly, and will also consume mites, scale insects and small caterpillars. The ladybug is a very familiar beetle with various colored markings, whilst its larvae are initially small and spidery, growing up to 17 mm long. The larvae have a tapering segmented grey/black body with orange/yellow markings and ferocious mouthparts. They can be encouraged by cultivating a patch of nettles in the garden and by leaving hollow stems and some plant debris over winter so that they can hibernate.

Hoverflies resemble slightly darker bees or wasps and they have characteristic hovering, darting flight patterns. There are over 100 species of hoverfly whose larvae principally feed upon greenfly aphids, one larva devouring up to fifty a day, or 1000 in its lifetime. They also eat fruit tree spider mites and small caterpillars. Adults feed on nectar and pollen, which they require for egg production. Eggs are minute (1 mm), pale yellow white and laid singly near greenfly colonies. Larvae are 8-17 mm long, disguised to resemble bird droppings, they are legless and have no distinct head. Semi-transparent in a range of colours from green, white, brown and black. Hoverflies can be encouraged by growing attractant flowers such as the poached egg plant (Limnanthes douglasii), marigolds or phacelia throughout the growing season.

Dragonflies are important predators of mosquitoes, both in the water, where the dragonfly naiads eat mosquito larvae, and in the air, where adult dragonflies capture and eat adult mosquitoes. Community-wide mosquito control programs that spray adult mosquitoes also kill dragonflies, thus removing an important biocontrol agent, and can actually increase mosquito populations in the long term.

Other useful garden predators include lacewings, pirate bugs, rove and ground beetles, aphid midge, centipedes, predatory mites, as well as larger fauna such as frogs, toads, lizards and birds. Cats and rat terriers kill field mice, rats, june bugs, and birds. Dogs chase away many types of pest animals.

Parasitoid Insects

Most insect parasitoids are wasps or flies. Parasitiods comprise a diverse range of insects that lay their egg on or in the body of an insect host, which is then used as a food for developing larvae. Parasitic wasps take much longer than predators to consume their victims, for if the larvae were to eat too fast they would run out of food before they became adults. Such parasites are very useful in the organic garden, for they are very efficient hunters, always at work searching for pest invaders. As adults they require high energy fuel as they fly from place to place, and feed upon nectar, pollen and sap, therefore planting plenty of flowering plants, particularly buckwheat, umbellifers, and composites will encourage their presence.

Four of the most important groups are:

Ichneumonid wasps: (5-10 mm). Prey mainly on caterpillars of butterflies and moths.
Braconid wasps: Tiny wasps (up to 5 mm) attack caterpillars and a wide range of other insects including greenfly. A common parasite of the cabbage white caterpillar- seen as clusters of sulphur yellow cocoons bursting from collapsed caterpillar skin.
Chalcid wasps: Among the smallest of insects (<3 mm). Parasitize eggs/larvae of greenfly, whitefly, cabbage caterpillars, scale insects and strawberry tortrix moth.
Tachinid flies: Parasitize a wide range of insects including caterpillars, adult and larval beetles, true bugs, and others.

Directly Introducing Biological Controls

Most of the biological controls listed above depend on providing incentives in order to ‘naturally’ attract beneficial insects to the garden. However there are occasions when biological controls can be directly introduced. Common biocontrol agents include parasitoids, predators, pathogens or weed feeders. These are particularly appropriate in situations such as the greenhouse, a largely artificial environment, and are usually purchased by mail order. Some biocontrol agents that can be introduced include;

Encarsia formosa. This is a small predatory chalcid wasp which is parasitical on whitefly, a sap-feeding insect which can cause wilting and black sooty moulds. It is most effective when dealing with low level infestations, giving protection over a long period of time. The wasp lays its eggs in young whitefly ‘scales’, turning them black as the parasite larvae pupates. It should be introduced as soon as possible after the first adult whitefly are seen.

Red spider mite, another pest found in the greenhouse, can be controlled with the predatory mite Phytoseilus persimilis. This is slightly larger than its prey and has an orange body. It develops from egg to adult twice as fast as the red spider mite and once established quickly overcomes infestation.

A fairly recent development in the control of slugs is the introduction of ‘Nemaslug’, a microscopic nematode (Phasmarhabditis hermaphrodita) that will seek out and parasitize slugs, reproducing inside them and killing them. The nematode is applied by watering onto moist soil, and gives protection for up to six weeks in optimum conditions, though is mainly effective with small and young slugs under the soil surface.

A bacterial biological control which can be introduced in order to control butterfly caterpillars is Bacillus thuringiensis. This is available in sachets of dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. The bacterial disease will kill the caterpillars, but leave other insects unharmed. There are strains of Bt that are effective against other insect larvae. Bt israelensis is effective against mosquito larvae and some midges.

A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma viride. This has been used against Dutch Elm disease, and to treat the spread of fungal and bacterial growth on tree wounds. It may also have potential as a means of combating silver leaf disease.

What You May See on Plants From BGH

Most of our beneficial insects do their work in the greenhouses at Odessa. Some, however, will travel with the plants. With that in mind, you may see some of the recruits we use to help us reduce the pest load in the greenhouse.

Amblysieus cucumeris/swirski. The most obvious evidence of these will be the small bags hanging on the hanging baskets. These bags contain some bran, a harmless mite (that eats the bran) and the mite Amblysieus cucumeris or A. swirski. These bags can stay on the baskets and will help control thrips for about a month after you receive them. You may also see some small piles of bran on the soil or leaves of some 4-inch pots like New Guinea Impatiens and Double Impatiens. This bran has the same contents as the bags. The Amblysieus cucumeris/swirski are both very small and you are unlikely to see them without magnification. If you do, the most likely places are deep within flowers and in the crotches of leaves and branches. (A. swirski, for those who may be curious, are more effective at higher temperature and humidity)

Aphidius colemani. These are small wasps that you might see flying around the basket. They will be about the size of a fruit fly but finer in shape with long, drooping antennae. They have a fairly erratic flying style but if you watch them, they will land and can then be identified. Secondarily, if there have been any aphids on the plants, then you may see aphid mummies. These look like a swollen aphid except that they are light brown in colour and may exhibit an exits hole where the aphidius has emerged.

Encarsia formosa. You are not very likely to see these. If anything, what you would see are blackened whitefly pupae on the backs of leaves, especially older ones. The parasitized pupae are about 1 mm across and it is quite possible to see them with the naked eye.

Eretmocerus eremicus. Again, these tiny wasps are not likely to be seen. You may see some parasitized pupae that have a lighter beige colour, contrasted with the blackened pupae left by the Encarsia Formosa.

What You Can Do

Once you get your plants home, there is really nothing to do regarding any of our helpers who may have come home with you. They will continue doing their jobs at your place.

There will, of course, be far more beneficial insects around to help you care for you plants if you refrain from using insecticides at home. Ladybug larvae and ladybugs, lacewing larvae and lacewings, hover flies, dragonflies, even toads and frogs will serve you very well as long as you do not kill them off or chase them out by spraying chemicals at the first sign of “bugs”. Not all insects are harmful pests. Rather than trying to kill everything with a chemical spray, why not learn a little about who is doing what in your garden? Remember, Mother Nature likes a balance – a large outbreak of aphids will usually attract a suitable number of aphid-eaters. Just a few predators can clean up many times their number in a single day. Let them do what they are meant to do

Another extremely important group of beneficial insects are the pollinators. Pollinators help keep plant species growing and producing year after year. As much as 80% of the world’s flowering plants require pollination to produce fruits and seeds — including two thirds of all food plants. Honey bees, butterflies, beetles, flies, and wasps are all well-known pollinators. A lesser known beneficial insect, the hover fly, not only pollinates plants in its adult stage, but feeds on soft bodied pests, like aphids, in its larval stage. Using chemical sprays risks harming these essential insects. If they’re gone, all of your best efforts spent fertilizing, pruning, watering and weeding will be wasted. Encourage pollinators whenever possible.

If, despite you best intentions to go insecticide-free, you find an insect pest getting out of control, try using a 2% detergent soap solution in a small spray bottle (it has to be 2% soap, mixed well with water). The sprayed soap solution will kill most garden insects on contact – even the good guys, so be careful with your aim! Nature isn’t sterile – we all know that chemicals can be harmful to us and to our environment; why use them if you do not need to? Let Nature take its course and perhaps even find out how you can encourage more beneficial insects to visit or even live in your garden.

Tips to Encourage Beneficial Insects at Home:

Don’t use chemicals. If you must apply pesticides, stick with less toxic ones such as insecticidal soap, Bacillus thuringiensis (Bt), neem oil and horticultural oil (note: these still harm all insects they come in contact with).
Provide water. A simple dish or pan filled with pebbles or coarse sand will provide drinking water for a variety of insects.
Provide shelter. Leaving some leaf litter and debris under shrubs may provide beneficial insects a place to hide during adverse conditions such as hot summer days.
Increase the diversity of your landscape. Grow a variety of plants to support a variety of insects. Don’t be overly concerned with neatness, either.
Do not use zapper lights that electrocute insects. These lights may kill more beneficial insects than pests.
Be ready for spring. The appetites of beneficials may peak before your garden does. Try to have an early bloomer, such as sweet alyssum or pansy, ready so the beneficial parasites can feed on nectar and pollen.
Choose their favorite plants. As a general rule, beneficial insects like tiny flowers that offer both pollen and nectar.