Biological Pest Control is a commonsense, long-term method of minimising pests. Two properties stand out in my memory as brimming with health and vitality. One was Jurlique's Adelaide Hills Herb Farm, 'Ngeringa', run on biodynamic and sustainable principles. The moment I stepped out of my car, I was struck by the sound of the garden – it was, quite literally, abuzz with life. The air was full of bees, hoverflies, flying insects of all kinds. When I walked through the garden beds, beetles scurried across petals. Tiny spiders could be found on almost every plant. The roses were in full bloom, with no sign of aphids. I have never before or since seen such a concentrated abundance and variety of insect life.
The second garden was the Urrbrae Rose Garden. To be honest, I did not expect to find a healthy garden – with such a concentration of roses and relatively few other perennials, this almost-monoculture garden should by rights be a buffet for pest insects. But no. The shrubs were sprinkled with ladybirds and a strange kind of beetle. I looked for aphids and could not find a single live one. Not one! In fact, the week before, a television crew had come to film a segment on biological control of aphids but had to cancel because they, too, could find none!
To utilise biological pest control in the garden, it's worth taking a look at the underlying ecological principles so you can most effectively apply them to your own conditions.
Natural Balancing Acts
In their country of origin, plants, animals and insects have evolved over millions of years to balance each other's populations. Insects evolved to feed on particular plants, or parts of plants, and then other insects evolved to feed on the insects feeding on the plants. If the plant becomes more prolific, the added food supply for the leaf-eating insect (pest or prey) increases their population as well. So the extra insects eat the extra plants, reducing their abundance to "normal" levels.
At the same time, with the extra prey insects as food, the predator insect population has risen as well, reducing the numbers of prey insect after a short lag.
In their home environment, therefore, and without outside intervention, abnormal events or chemicals, plant and insect populations remain in balance, with the abundance of plants, prey and predator insects fluctuating constantly but marginally, keeping each other in check and preventing excessive peaks in population.
Upsetting the Balance
What happens when we take something out of the equation? Move a plant to an environment without bringing along the insect that feeds upon it, for example? Or transporting the insect and plant, without bringing along the insect's predator? Or having all present, but spraying a chemical to kill the pest insect? Clearly, there are several potential scenarios.
In Australia
Although Australia is known for some of the greatest successes in biological pest control, it also has the dubious distinction of having some of the worst failures. First, a success.
Prickly pear (Opuntia stricta) was first recorded as introduced in the early 1800s as stock feed and a hedging and garden plant, but it spread incredibly quickly, covering 25 million ha by 1925 in NSW and Queensland. Paddocks were overrun with prickly pear; with no room for stock or crops, numerous farmers were driven off their land. Parliaments passed Control Acts, poisons and physical methods of control were tried to no avail. And then, in 1926, Cactoblastis caterpillars, which feed on prickly pear, were introduced after rigorous testing to ensure they would not attack other plants. In just six years, most of the impenetrable stands of pear were gone, and farmers restocked their land. The Cactoblastis caterpillar in Australia is still considered one of the most successful examples of biological control in the world.
For an example of biological control gone wrong, we only need look at the cane toad, which was introduced in 1935 to eat the cane beetles that damaged sugar cane crops. Unfortunately, the toads ate everything but the beetles and, without natural predators or diseases in Australia to control their own population, they thrived; we all know what has happened since then.
Other combinations
So biological controls may be insect predators to control plants (Cactoblastis), insect predators or parasites to control insect pests (parasitic wasps on aphids, nematodes on millipedes, predator mites against red spider mite), viruses or diseases (pathogens) to control pest plants (eg. rust on blackberry, bacteria on caterpillars) or pest animals (myxomatosis, calicivirus for rabbits). Because biological controls are living populations, they are unlike chemicals, which need to be repeatedly reapplied over a wide area. Instead, the biological control population will spread and increase – and then decrease – in response to the pest population (remember those graphs?). In fact, a single release of a biological control agent in one place can spread throughout an entire pest population, throughout the country.
In the Home Garden
Most of the insect pests in our gardens can be controlled via biological means, and organic, permaculture, sustainable and biodynamic principles to varying degrees all encourage the development of a more natural, balanced ecosystem within the garden. Your patience, and NOT SPRAYING insecticides, are essential for success. Remembering those graphs, you know that in a healthy garden, predator populations build up after a short lag time to control pests – but not if you go spraying the pest first!
Although organic pesticides are regularly promoted as less toxic than chemical ones, in the context of establishing biological control, both are equally damaging as they severely disrupt the natural predator-prey response cycle. In fact, biological controls often require a few years and the sacrifice of a few blooms for predator populations to build and, during this time, you'll need to resist the temptation to spray even heavily pest-infested plants, for it is these that will provide prey for control insects.
Systemic pesticides such as Confidor, which are consumed only by insects feeding on the plant, still upset the prey-predator cycle. Start spraying, and you are stuck with spraying.
At Jurlique's Ngeringa Farm, no chemical sprays have been used by them at all. At Urrbrae, no pesticides – organic or chemical – have been sprayed on the roses for more than a decade. Instead, biological controls, such as the predatory wasp Aphidius rosae, have been introduced. The complete absence of pesticides has allowed large predator populations of wasps, ladybirds, spiders, hoverflies and lacewings to become firmly established, and this permanent foundation ensures their numbers soar correspondingly quickly in response to aphid explosions, reducing pest numbers before they can cause serious damage.
Although predator insects will gradually build up in your garden over time, you can speed the process by purchasing them to control everything from aphids, mealybugs, two-spotted mites, codling moth, whitefly and more:
And of course Dipel, whose active ingredient is Bacillus thuringiensis, a bacteria that attacks caterpillars, has long been available to control caterpillars on crops. "Integrated Pest Management" in plant nurseries, greenhouses, and in broadscale farming nowadays often includes biological control principles.
Fortunately, unlike monoculture crops or broadscale farming, home gardens can tolerate a much higher level of pests, and home gardeners can afford a few years of higher pest numbers, without losing our income as predators establish. The old spray-everything-in-sight philosophy has long gone, with gardeners today knowing that a sterile garden equates to an unnatural and unhealthy one. The plethora of organic products and options in gardening stores is testament to that increased knowledge; biological control of garden pests is one further step in the right direction.
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