Alison Evans - former DOC Invertebrate Ecologist
By increasing the variety of insects in your garden you can maintain a healthy balance between pests and beneficial insects, reducing the need to use insecticides. Frequent use of insecticides not only costs you money but can cause some insects to build up a resistance to certain sprays.
Biological control has been used around the world for hundreds of years to control garden pests. This is a type of population management where beneficial insects are attracted into gardens or crops to suppress nuisance insects.
Ladybird and aphid
Insects such as lacewings, praying mantis, ladybirds, hoverflies, ground beetles, earwigs, native bees, native wasps and assassin bugs all control insect pests. Spiders, centipedes and some mite species are also effective hunters of insect pests.
Planting shrubs which have lots of flowers is an excellent way to attract beneficial insects into gardens. There are a number of native plants that provide suitable nectar and pollen for insect food.
- Olearia spp.
- Muehlenbeckia astonii - shrubby tororaro
- Pittosporum tenuifolium - kōhūhu
- Pittosporum eugenioides - tarata / lemonwood
- Plagianthus regius - mānatu / ribbonwood
- Cordyline australis - ti rākau / cabbage tree
- 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 attract exotic insect pests. So it may 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 which live in 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 using 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 - a guide to pest control in the home and garden, 1998, Dunmore Publishing Ltd. by Assoc. Prof. Bruce Chapman of Lincoln University.