One of the big changes in commercial horticulture over the past 20 years has been the shift from pesticides to a greater reliance on beneficial insects. An entire industry has grown up to supply commercial growers and some keen gardeners with beneficial insects to wage war on pests and diseases.
This type of pest control is known as Integrated Pest Management (IPM). Some of the insect and mite pests now controlled routinely with other insects include two-spotted mite, aphids, whitefly and thrips. The main beneficial insects are ladybirds, predatory wasps and certain mites. These insects may eat the pests or parasitise eggs or pupae.
In a garden where there’s little or no use of toxic pesticides, plants develop their own in built IPM systejs, which is why it is important to check pests for signs of natural control before reaching for a spray.
One of the Australian pioneers of IPM is James Altmann, co-director of Biological Services in South Australia, who was recently in Tasmania visiting growers and checking up on beneficial insect populations. He says among the factors driving the switch to IPM has been the failure of many chemicals due to insect resistance and a greater awareness of health and safety.
IPM uses all forms of pest control including quarantine and hygiene, cultural controls, varietal selection for pest or disease tolerance, beneficial insects and mites, as well as selective chemical controls.
By relying on beneficial insects, mites and the occasional pest-specific chemical control, growers are reserving other chemicals as an absolutely last resort for pest control. “Without preserving chemicals in this way,” James warns, “we won’t have them in the future as pests are rapidly building up resistance and not as many new chemicals are being developed.”
Right now James is very excited about a native insect, which has big promise as a biological control. The small native beneficial mite called Typhlodromalus lailae is under trial in protective cropping situations against thrips, whitefly and pest mites.
“It has been recognised for many years but was difficult to rear in the lab in large numbers,” explains James. “T. lailae is a native Australian predatory mite naturally present in many mild, humid, coastal and hinterland districts.”
Insect welcome mat
One of the perceived downsides of biological control in gardens is that gardeners need to tolerate a low level of pests to maintain the population of beneficial insects.
Tolerating pests is also important if you want to enjoy seeing insects such as butterflies in the garden. Autumn is a time when lots of butterflies are about but for them to have reached adulthood, they need to have spent time as plant-munching caterpillars.
I was thrilled this week to see a Macleays swallowtail in my garden and was glad that a caterpillar survived to pupate into such a beautiful creature. The Macleays swallowtail is found across western Tasmania and has distinctive green and white dots on its black wings – look out for it.
It is also necessary to have areas in the garden where beneficial insects can live and breed when they’re not on garden plants. Insect hotels (attractive collections of nesting hollows such as bamboo tubes, bricks, twigs or stones) are very popular but insect homes don’t need to be so fancy. Areas of the garden left a little wild are often insect havens. Small shallow water bowls can provide water, which also helps bring insects into gardens. Fill shallow containers small stones so bees and other insects can sit on the wet stones to drink rather than risk falling into the water and drowning.
by Jennifer Stackhouse