Guidelines from members of the Auckland Branch of the Entomological Society of New Zealand
During 2010 members of the Auckland Branch were consulted about ways by which insects and other invertebrates could be encouraged in gardens. Firstly we asked what kinds of insects should be encouraged and which should be discouraged. This revealed that some insects could be both desirable or undesirable according to the aims of the gardener. For example the Chinese paper wasp, Polistes chinesis (Hymenoptera: Vespidae) is desirable as a biological agent for caterpillars feeding on vegetables and flowers, but is undesirable for people wishing to encourage monarch butterflies.
In order to encourage insects and other invertebrates its necessary to provide both food and suitable places for them to live. Basically this requires creating diversity of plants and kinds of habitat. The details below provide ideas about how to do this. If you have any additional suggestions please contact Nick Martin (Nicholas.Martin@plantandfood.co.nz).
1. What kind of insects and invertebrates should be encouraged?
- Pretty ones, e.g. butterflies, moths (including cabbage tree moth, ladybirds, cicadas, dragonflies and damselflies.
- Ones with striking appearance, e.g. weta, Huhu beetle, mantids.
- Those that are good for the soil, e.g. earthworms.
- Those involved with recycling dead plants and other organisms, including dead wood feeders, e.g. native cockroaches, millipedes, slaters, amphipods.
- Natural enemies, including:
- Herbivores that feed on weeds, e.g. cinnabar moth (feeds on ragwort).
- Predators, e.g. ladybirds, centipedes, mantids, spiders.
- Note: Chinese paper wasp is very good at controlling green looper caterpillars on tomatoes.
- Pollinators, e.g. honey bees, bumble bees, native bees, wool carder bee, flies, beetles.
- Native insects, especially rare and endangered species in an area, e.g. yellow and red admirals in Auckland.
2. Should any insects and invertebrates be discouraged? If so which?
- Adventive species competing with native insects, e.g. African mantid.
- Species that threaten our native species, predators and parasitoids form other countries.
- Insects that may upset neighbours—German and common wasps (Vespula species), paper wasps (Polistes species).
- Pests of garden plants, white butterfly, garden snails and some slugs.
- Argentine ant.
3. What kind of plants are good to provide pollen and nectar during different seasons?
Flowers are needed for pollinators and as food for other desirable insects such as butterflies, moths, beetles, predators and parasitoids.
- Have plants flowering all months of the year. Also have flowers of different shapes and sizes so that they are suitable for a variety of insects. Include plants of:
- The carrot family with the small flowers in flat topped umbels.
- The salvia family, these favour the wool carder bee.
- The daisy family.
- Red valerian is good for moths.
- Heliotrope, Sedum, Hebes.
- Buckwheat and Phacelia flowers produce lots of pollen.
- Encourage flowers in the lawn. Mow it long and infrequently. Plantains are good for hoverflies.
- If there is room, have a meadow. Cut the vegetation once a year.
4. Food plants for butterflies and day flying moths
These insects require special food plants:
- Swan plants, Gomphocarpus species, for monarch butterflies.
- Nettles, Urtica species, for red and yellow admiral butterflies.
- Muehlenbeckia species for copper butterflies.
- Cassia for long-tailed blue butterfly.
- Lotus for small blue butterflies.
- Magpie moth (Nyctemera) seems to like weedy Senecio species, and possibly not the ornamental varieties.
5. Native plants to encourage native insects
Adult stem borer weevil, Rhadinosomus acuminatus on stem of host plant, Toatoa (Haloragis erecta) (photograph by Nicholas Martin).
Most native herbivorous insects only feed on native plants. The following plants are both beautiful and support a variety of native insects:
- Kowhai, Sophora species.
- Coprosma species, especially C. robusta.
- Pittosporum species, especially P. crassifolium, P. tenuifolium and P. eugenoides.
- New Zealand flax, Phormium species.
- Native Cortaderia species (toetoe).
- Cabbage trees, Cordyline species.
- Manuka and kanuka.
- For moth caterpillars: Hoheria, Sophora, Hebe, Pittosporum, Pseudopanax, Cordyline, Leptospermum and Macropiper.
6. Encouraging soil and litter fauna
Create a diversity of surface layers on the ground and have a variety of large objects of different textures lying on the ground:
- Large pieces of bark (still with the curved shape of the trunk/branch), rough side upwards, that will provide dark spaces with high relative humidity. The bark can be combined with lawn clippings and other compostable material. This will encourage springtails and predators.
- Bricks and pieces of old concrete on soil and/or rough chopped vegetation and lawn clippings.
- Rotting wood also on soil or dead vegetation.
- Piles of coarsely chopped vegetation, in the open or under shrubs and trees.
- Lawn clippings in piles or spread around plants.
- Chipped branches spread on the ground. These can encourage certain fungi that provide food for invertebrates. The fruiting bodies of some fungi are designed to attract flies to disperse the spores.
7. Creating diverse habitats
Create a diversity of habitats:
- Areas of stone (large pebbles or rocks) loose on the ground or in rough dry stone walls.
- Bark segments and lots of dead leaves from deciduous trees.
- Wood, recently dead or rotting.
- Coarse material can be created by running the lawn mower over piles of twigs and branches. Piles of this material encourages many litter living insects.
- Where practical have an area of firm (compact) bare soil of clay in which native bees, tiger beetles and ant lions can make holes and live. Clay banks also encourage nesting of native bees.
8. Creating special habitats
Special habitats can also be created:
- Weta motels can be made from short lengths of bamboo tied together bound to a tree trunk.
- Similar bundles of bamboo can be hung in trees. These make dwellings for many kinds of insects such as earwigs, slaters, beetles, beetles and tunnel web spiders.
- Short lengths of narrow bamboo placed horizontally in a stack like firewood make nesting sites for native wasps and other insects.