Green Vegetable Bugs - Nezara viridula
GVB is a major pest in many crops including soybeans, cotton, sweetcorn, macadamia nuts in some areas, pecans and tomatoes.
GVB can breed within many crops while other crops are plagued by the adults that fly in from neibouring areas.
Trissolcus basalis - Egg parasitoid
Trissolcus is a small black wasp and about 2 mm long. Its the main egg parasitoid of green vegetable bug in Australia. The female wasp uses the bug eggs to rear their own young. It is commonly found in crops all over Australia
Under the right conditions, they can make a major contribution to the control of this important pest. They are typically in low numbers coming out of winter and will build up slowly if given a chance. However, spraying in crops usually prevents them getting to high levels.
District wide benefits?
Recent experience with Trichogramma wasps against macadamia nutborer has shown that area wide benefits can be achieved from widespread mass releases of parasitoids, not just the short term impact within the crop. This is likely to be the case for other parasitoids like Anastatus and Trissolcus and Trichopoda another GVB parasitoid.
High levels of parasitism from local Trissolcus have been observed later in the season. This suggests the wasps are very capable given the right conditions.
By making mass releases this should be more common and help to reduce overwintering bug populations. The more farms in an area making releases the more likely this is to happen.
Selecting sites suitable for Trissolcus release
For more general info on green vegie bugs see the Qld DAF Info Sheet:
Making Trissolcus releases
At this stage its unknown what release rates of Trissolcus are needed to make a useful difference in crops. However, we do know that natural populations of Trissolcus can make a big difference later in the season so releasing the wasps early in the life of the infestation is very likely to accelerate this process - as we have found with other biocontrol agents. The only way to find out is to try in a way that we think is likely to be successful.
For macadamias, we suggest starting releases in early spring into headlands where you think bugs are coming from.
For short term crops like soybeans and tomatoes, regular releases starting a several weeks before the anticipated bug egg laying period is likely to have the most effect. If there are know sources of GVB nearby and accessable then wasps should be released there as well.
In this way early laid bug eggs can be parasitised and therefore slow the bug increase right at the start. Each female wasp can parasitise over 200 GVB eggs and develops from egg to adult in just 12-14 days. So if many bug eggs are being laid the wasp numbers can increase and spread markedly in the following weeks and have a major impact on GVB numbers.
For more information on GVB and Trissolcus and ordering go to the Trissolcus Web Pages
Pdf's for download:
GVB eggs are laid in tight clusters of near 100 eggs.
Immature stages of GVB
If the food is good a GVB female will lay a raft of eggs.
Trissolcus laying its own egg into a GVB egg