The principal advantage of encouraging predatory insect numbers is it lets growers dismount the pesticide treadmill, while saving themselves money. But rather than simply letting the weeds grow, Professor of Ecology at Lincoln University, Steve Wratten advocates focussing on meeting what the various insects’ needs are.
Tiny predators with gigantic appetites, hoverfly larvae numbers can easily be encouraged to rid your crop or garden of aphid infestation, allowing you to stay spray-free.
"Even the lions of Africa don’t kill 20-30 antelopes a day, yet hoverfly larvae each eat around that many aphids a day during their three week lifecycle, making them major predators. The female produces around 100 eggs, and the heavier the aphid infestation the more eggs the female hoverfly seems encouraged to lay," says Professor Wratten.
Hoverfly numbers can easily be encouraged through the planting of phacelia or tansy leaf, available from any seed merchant. Phacelia planting should occur monthly to ensure it is always in bloom to feed the hover flies. Covered in small blue flowers, phacelia gives the female hoverfly protein for egg maturation and nectar for energy, vital ingredients totally absent when field margins are sprayed with herbicide.
Beetle banks are another effective way of creating favourable predatory insect habitats. Known in England and Europe to foster predator densities of over 1000 per square metre, in Lincoln University beetlebank trials, predator densities reached 2000 per square metre, with full grass cover for the first time two years after their establishment.
"The benefits upon the crop are being noticed, while the creation of beetle banks is both simple and inexpensive and doesn’t interfere with our growers’ normal farming practices," says horticulturalist Anthony White.
Creation of a beetlebank is simply a matter of raising a 30cm high/1.5-2m wide earth bank surrounding your crop, perhaps running through it, and sowing this with a 50/50 mixture of Cocksfoot and Yorkshire Fog grass seed. Size of the field will dictate placing of the banks but generally, the bigger your field the more ridges you need. Two or three years after creation the banks will have developed into suitable overwintering insect and spider habitats and your crops will begun to benefit from their pest predation. The ridges are easy to relocate if farming practices change.
Buckwheat is another haven for beneficial insects, flowering within six weeks and feeding parasitoids of the leafroller caterpillar. These parasitoid wasps lay a microscopic egg inside the caterpillar, killing it by eating it from the inside out, just like the movie Alien. Two season’s of New Zealand research into buckwheat under apple trees revealed twice as many leafroller parasites were present in the trees with flowering buckwheat underneath them, compared to trees without buckwheat which were only a few metres away. Though the buckwheat plots were small the presence of buckwheat had a big enough influence to double the number of leafrollers killed.
Encouraging bumblebee pollination of your crops is a very effective natural way to increase both the fruit yield and the size of the crop. Originally imported from England to pollinate red clover, the clock has turned full circle - now any grower can easily foster their own bumblebee populations, so enhancing the benefits first gained by pastoral farmers over a century ago.
More on Beneficial Insects
Beneficial Insects and Mites
University of Florida Extension - Institutute of Food and Agricultural Sciences
This website contains a database of publications, including a section on Organic Farming.
"Many insects and related anthropods perform functions that are directly or indirectly beneficial to humans. They pollinate plants, contribute to the decay of organic matter and the cycling of soil nutrients, and attack other insects and mites that are considered to be pests. Only a very small percentage of over one-million known species of insects are pests...
Plants That Attract Beneficial Insects
This article is posted on the website Answers to Questions that Bug You. While of more use to our United States visitors, it also contains information of use to New Zealanders. This website is compiled by an amatuer enthusiast and is packed with useful information, including insect identification pics.