Controlling insects naturally
Controlling insect pests the natural way
Alison Evans DOC Invertebrate Ecologist
Managing the pests in your garden using natural control methods is nothing new. In fact, biological control has been used around the world for hundreds of years. Biological control is best explained as a type of population management where beneficial insects are attracted into gardens or crops to suppress nuisance insects.
Enhancing the diversity of insects in your garden helps to maintain a healthy balance between pests and beneficial insects, reducing the need to use insecticides. Frequent use of insecticides is not only costly but can cause some insects to build up a resistance to certain sprays.
What people don't realise is that many of the insects commonly found in gardens are beneficial to gardeners and that some insecticides can be harmful to these species.
Insects such as lacewings, praying mantis, ladybirds, hoverflies, ground beetles, earwigs, native bees, native wasps and assassin bugs, control insect pests. Spiders, centipedes and some mite species are also effective hunters of insect pests.
Planting shrubs with abundant flowers is an excellent way to attract beneficial insects into gardens. There are a number of native plants that provide suitable nectar and pollen resources.
These include:
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Olearia spp.
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Muehlenbeckia astonii - shrubby tororaro
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Pittosporum tenuifolium - kōhūhu
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Pittosporum eugenioides - tarata / lemonwood
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Plagianthus regius - mānatu / ribbonwood
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Cordyline australis - ti rākau / cabbage tree
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Hebe spp.
Plants with small, open flowers tend to be more attractive since most native insects have short tongues, an adaptation to the short corolla tube on many native flowers.
Prof Steve Wratten from Lincoln University's Ecology Group, says "The trick is to ensure that there is a continuous supply of the right types of flowers available for beneficial insects from spring to late summer. Plants such as cock's foot grass are also important to provide refuges for the insects to over-winter in".
Many of the plants we grow (particularly vegetables) are not native to New Zealand and as a result, they tend to have a characteristic complement of exotic insects associated with them. So it might also be worth considering planting exotic plants such as Phacelia (tansey leaf), Allysum or buckwheat, which provide excellent pollen and nectar resources for beneficial insects resident in vegetable crops.
The following principles will help to enhance the number of beneficial insects in your garden:
- Providing flowers suitable for beneficial insects.
- Providing refuges such as long grass or hedges for beneficial insects to over-winter in.
- Minimise spraying and only use insecticides specific to the pest you want to target.
- Successively plant to provide a continuous source of nectar and pollen resources.
- Try to coincide flowering with the life-cycle of the insects in your garden.
For more excellent ideas on controlling garden pests, try reading Backyard Bugs by Assoc. Prof. Bruce Chapman of Lincoln University
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