Weed species have a huge impact on native flora and fauna aswell as agricultural systems in many countries. In New Zealand there are 20, 000 non indigenous plants with about 240 of them being considered pests. Ideally plants that could potentially become weeds should not be allowed into NZ. But if they do make it into NZ the next best scenario is early detection. Often by the time plant pests are detected they are widespread and out of control. Chemical control of these pests can be costly, time consuming and risks the plant becoming immune or partially immune to chemicals. Many plant pests have highly specific insects that prey on them and can be highly effective in suppression of pest spescies.
This paper argues in favor for the advantages of bio-controls on plant pests. Initially research costs to find and test the effectiveness of insect controls can be high but the long term effects on the control of plant pests can outweigh the initial costs. Also the testing may go on for a number of years before the control agent is released into the environment as bio-controls are often non-reversible and may have an impact on native ecosystems.
An example of a bio-control program is the Heather, Calluna vulgaris (Ericaceae) which is a low growing perennial shrub.The heather beetle, Lochmaea suturalis (Coleoptera: Chrysomelidae) was researched for 5 years before being released as a control agent. From 1991 to 1993 choice feeding tests occurred. Larvae and adult beetles were exposed to a test plant in the presence of heather. 1993-97- tests on the ovipositor preferences and rates, larval and adult survival rates on plants from choice tests, quarantine and rearing in confinement to remove a parasitic microsporidian from the beetle cultures. 1996-1997 releases into Tongariro National Park. Following the release of the heather beetle ongoing monitoring of the spread and impact of the beetle on the heather plant. Ecological studies are needed following the release to show the impact of the beetle on the population of the plant.
Introductions of insects also causes huge environmental impacts as pest plants can. A well documented example of this is the accidental introduction of the Oak leafminer, Phyllonorycter messaniella (Zeller) which began to attack Nothofagus spp. The leafminer became so abundant that it damaged its natural hosts as well as Nothofagus spp. After introducing two species of parasitic wasps the leafminer was successfully controlled to a level where they have not been reported to attack Nothofagus since.
