Biological control insects
A range of beneficial insects and mites are available for biological control on the nursery. 

These beneficial organisms can be split into predators and parasites.

Predators
These are organisms such as lacewings, mites and lady beetles, which feed on a number of their natural prey. They often attack different life stages of the pest and even different pest species. Some can supplement their diet by feeding on alternative food sources, such as pollen, nectar and fungi. Those picked for biological control are voracious feeders and predators are often more robust than parasites.

Predatory mite Persimilis feeding on red spider mite

Parasites
These are usually tiny wasps that deposit an egg into the ‘host’ pest, though there are parasitic nematodes (microscopic worms) now available. The larva that hatches ultimately consumes and kills the pest. Each parasite completes its entire development on an individual host. Sometimes many parasites may emerge from one pest. The advantage of using parasites is that they are usually extremely well adapted to their natural host and are very good at finding them even when numbers of the pest are relatively low.

The wasp parasite Aphystis lingnanensis laying its egg into red scale

About the use of beneficial insects
It is important for the nursery crop protection manager to discuss the use of predators and parasites thoroughly with a supplier. Where possible, order beneficial organisms well in advance. Do not wait until a serious pest problem has developed before electing to release them. Beneficials are best released early in the season while pest pressure is relatively low. Regular ‘top-up’ releases made following the initial full release will give optimum results in many situations.

Cryptolaemus larva and adult beetle feeding on mealybug egg mass

It is important for pest managers to remember that beneficial organisms should not be regarded as just another pesticide. Their successful use will always require good understanding of issues such as pest life cycles, accurate identification of pests and beneficials, and compatibility with other crop management practices.

Ossie mite 1, potential predator of WFT

Tomorrow’s biological controls
There are two recently arrived pest insects in Australia for which biological controls are being currently developed. They are; Western flower thrips (WFT) (Frankliniella occidentalis) and Silverleaf whitefly (SLW) (Bemisia tabaci biotype B). Both these nursery pests have proved devastating overseas, they have arrived with resistance to many pesticides and are capable of developing new resistance quickly. WFT is a very efficient carrier of the Tomato Spotted Wilt Virus.

Researchers at NSW Agriculture Gosford and CSIRO Entomology in Canberra have been searching for native beneficial insects to use against both these pests. They have identified some potential candidates and with the help of commercial insectaries are now beginning trials for mass rearing. If these are successful, field trials in nurseries will begin next season. 

Encarsia wasp with parasitised whitefly scales

There is continuing research to find biological controls for as many common pests as possible, these include such pests as Broad mite and Tomato russet mite and nematode research is identifying candidates for controlling turf grubs and other soil born pests.

One of the major reasons given for not adopting biological control within an IPDM program is the perceived risk of failure. This is perfectly understandable, but should be seen in context. It is just one of many such everyday decisions facing nursery managers. There are similar risks involved in the introduction of new plant lines, a change of growing media or the introduction of quality assurance and accreditation schemes. As with any of these, the adoption of biological control should be approached with expert advice and support and a realisation that some initial time and effort is required to eventually reap the rewards for the whole business.

Why biological control?

Public opinion
Concern for the impact of pesticides on both human and environmental health is now firmly established on the public and political agenda. In Europe, the USA and Australia nursery industry bodies are highlighting the use of biological control in nursery production to demonstrate a positive response to these concerns.

Quality assurance and accreditation
Quality assurance is being recognised throughout the nursery industry as a necessary part of modern working practices. The nursery industry’s own accreditation scheme has as one of its major aims to ‘encourage the use of environmentally sound work practices’. Proven adoption of IPDM practices is part of the accreditation requirement and the use of biological controls is a major consideration when implementing IPDM.

Pesticide resistance
Many established nursery pests can rapidly develop resistance to insecticides, sometimes within only 2-3 seasons of use. Coupled with the limited number of pesticides being registered for nursery industry use in Australia, this makes IPM using biological control one of the best long-term options for pest management. On top of this there is the added problem of new imported pests appearing with already established resistance to many chemical controls. (e.g. Western flower thrips and Silverleaf whitefly).
 
 

Economics
There can be significant economic savings from an established biological control program. Successfully managing and maintaining biological control of particular pests requires the presence of someone on the nursery with more than a rudimentary knowledge of crop protection. Whether this is one employee given special responsibility for effective crop protection or the use of an IPDM expert scout, the savings from unnecessary chemical applications can often be far greater than the cost of scouting or training.

Thanks to both groups for the use of photographs. Also thanks to the Australasian Biological Control association for photographs of predators and parasites.

1 Secretary of Australasian Biological Control, the association of beneficial arthropod producers.
P.O. Box 436, Richmond, NSW 2753. 

Further reading
A step-wise programme for practising IPM, The Nursery Papers, issue no 1997/005

Accreditation for business success, The Nursery Papers, issue no 1998/004

Managing Western flower thrips, The Nursery Papers, issue no 1997/012

Silverleaf whitefly: management of a nursery pest, The Nursery Papers, issue no 1997/009

The Good Bug Book, (book), Ed. Broadley, R & Thomas, M. (1995), Queensland Department of Primary Industries, publications department, Brisbane. Ph 1800 816 541