Trichogramma pretiosum was brought to Australia from Norh America in the mid 1970's and released in the Ord River district in north-west W.A. and in small quantities at St George on the Darling Downs in SE Qld. The wasps established well in the Ord but there is doubt whether they established at this time on the Darling Downs.
In 1995, Brad Scholz from the QDPI Toowoomba obtained samples of the Ord River strain, bred them up and made small releases at several sites on the Downs and Lockyer Valley. This time there was no doubt about establishment. The Lockyer Valley has proved a very suitable environment for pretiosum with a wide range of crops and pests and a relatively mild winter. By December numbers are ofter high. On the Downs, pretiosum has been slower to establish but now reappears in many areas in low numbers each spring and given the opportunity will increase to high numbers by February.
Pretiosum has had a major impact in the sweet corn industry the Lockyer Valley. Combined with "soft" insecticides like Gemstar® and Success® the industry has turned around from the brink of collapse due to heliothis resistance to broad spectrum insecticides. Pretiosum has now become established in other districts including Bundaberg and areas of the Sunshine Coast and parts of inland NSW. The extent of this establishment is unknown at present.
Mass releases of pretiosum enables quick establishment so that growers can get straight into a "soft" IPM program rather than using up "soft" sprays waiting for local Trichogramma to move in and build up. "Soft" sprays saved in this early period can be kept aside for use later in the season if necessary. Local Trichogramma may or may not contribute.
Pretiosum has been particularly successful in tomatoes, melons, zucchinis, sweet corn, maize, sorghum. soybeans and cotton. Very high levels of parasitism (near 100%) are common, greatly reducing the need to apply chemical insecticides.
In recent times a number of "soft" biological and chemical insecticides have become available and these have made it easier to benefit from Trichogramma and other beneficial insects. See Chemicals for details.
Trichogramma pretiosum although a tiny wasp is a very 'aggressive' parasitoid and can increase to very high numbers resulting in near to 100% parasitism in favourable conditions. High Trichogramma activity enables reductions in chemical applications and reduces resistance pressures on those products.
For field crops, inoculative releases early in the life of a crop are recommended. In this way, release rates can be relatively low and the wasps do not need to be evenly distributed through the crop - reducing the application time and cost. This method uses the increase in wasp numbers within the crop over several generations.
Trichogramma live for about 10 days and can parasitise about 50 eggs in that time. In summer it takes about 8 days for wasps to emerge from parasitised eggs. Typically 3 wasps emerge from each parasitised egg. This high reproductive rate enables huge numbers of wasps to develop rapidly.
Pretiosum male
T. pretiosum female laying eggs into a moth egg
"Black" parasitised heliothis egg in corn silks.
