Biological control of the European corn borer
Biocontrol of the European corn borer using trichogrammas, insects that lay their eggs inside those of pests, thus allowing population control.
Biocontrol of the European corn borer using trichogrammas
Within corn plantations, the effectiveness of trichogramma was observed to effectively control the two main pests, including the European corn borer (Ostrinia nubilalis).
Trichogrammas lay inside the eggs of the pest, which leads to a reduction of their populations to a level comparable to insecticide use when conditions are optimal.
Where to use them?
Trichogrammas can be released in fields and greenhouses as a biocontrol agent to control pest populations, especially lepidopterans.
How to use them?
Most commercial products are sold as cardboard strips with trichogramma eggs glued on them. Other products exist as perforated organic capsules (made of cellulose or starch), containing about a hundred female trichogramma larvae intended to be released using a drone. Under favorable conditions, the larva develops in 7 to 8 days before it can start laying its eggs inside those of the European corn borer.
These products can be released in the field either by:
- By drone: Mass release of trichogrammas in fields using a drone. This must be done carefully because their life cycle is short, so they must be released in the field only when they are at the egg stage. To control a large number of pests over a wide area, the drone release technique must be repeated precisely. Skyinnov has marketed a trichogramma release system using beads, the T-drop spreader.
- By hand: Release of a small quantity of trichogrammas over a limited area by placing the cardboard strips in the area to be treated. These strips contain trichogramma eggs that will hatch throughout the season and colonize pest eggs.
Trichogrammas must not be used in combination with pesticides as they are sensitive to them (link). If pesticide use is necessary, they should be applied directly to the soil or used as granules. This can avoid contact with host eggs and trichogramma wasps while allowing control of plant pests that feed on plant tissues.
When to use them?
The effectiveness of trichogrammas depends on the timing of their release; they must be released when borers populations are active and laying eggs. The precise timing varies depending on the crop or targeted pest, but it is generally recommended to release trichogrammas when the egg-laying of borers is at its peak.
For example, a study published in the journal Crop Protection observed that trichogrammas were more effective against the tomato fruitworm (Helicoverpa zea) when released three days after the first capture of a moth in pheromone traps.
Another study, published in Entomologia Experimentalis et Applicata, observed that trichogrammas were more effective against the codling moth of apple (Cydia pomonella) when released at the green bud stage of apple development.
Advantages
Using trichogrammas can help minimize pesticide use.
- Their use contributes to sustainable agriculture and minimizes damage to the environment.
- They leave no residues in the environment.
- Trichogrammas target the parasites they control, i.e., Ostrinia sp. They are also known to have a broad host range (link).
Limitations
- Host specificity: Trichogramma wasps are specific to the eggs of the borers they parasitize. This means the correct trichogramma species must be selected for the pest to be controlled.
- Environmental sensitivity:
- Trichogrammas are sensitive to temperature and humidity. They perform optimally at temperatures between 20 and 34°C and at 75% humidity.
- Extreme conditions can lead to poor field results.
- They cannot be used simultaneously with pesticides as this reduces their effectiveness.
- Their range of action is limited; they are not effective against all stages of the borer. They are only effective against the eggs, meaning they do not provide a complete solution for pest control.
- Proper timing of release: They must be released at the right time to be effective. Farmers must monitor borer populations and release trichogrammas when moth egg-laying is at its peak.
- Labor cost: Manually placing the cardboard strips containing wasps on corn plants requires more labor (link).
- Slow action: Trichogrammas may have a slower impact on corn pests if not released at the right time and under the right conditions.
Cost
Trichogrammas are relatively inexpensive compared to chemical pesticides. The expenses related to using these wasps mainly depend on the deployment methods. This includes labor needed to hang the cardboard strips on corn plants or the use of drones to release trichogrammas. The cost of trichogrammas varies by supplier, quantity ordered, and country. In France, trichogrammas can be obtained from various suppliers and cost between €38 and €45/ha[1].
How to obtain them?
Trichogramma wasps can be purchased from biological control agent suppliers such as Koppert, Bioline Agrosciences, De Sangosse, etc. They are generally shipped as pupae inside host eggs, glued on small cardboard strips or as sprays.
This page shows different application methods of trichogrammas offered by various suppliers.
Testimonials
Some testimonials on successes in agriculture where trichogrammas have been used:
- In northeast China, the use of trichogramma wasps to control the European corn borer in cornfields increased from 600,000 to 5,500,000 hectares between 2005 and 2015, covering 35% of cornfields.
- In rice fields, Trichogramma japonicum showed good results, and in sugarcane, T. chilonis has been released since the 1960s, preventing about 20% of yield losses.
- Some studies suggest that using multiple trichogramma species and combining their releases with other biological control organisms can be more effective. In Colombia, integrating trichogrammas with Bt (Bacillus thuringiensis) and other organisms reduced insecticide use by 50% in tomato and cassava crops.
- Within the French BIDIME project[2], trichogramma was considered an effective solution to protect jasmine ornamental plants against several lepidopterans (link).
- Thierry Houx is a winemaker part of Dephy, a network of farmers experimenting with ways to reduce insecticide use. He explains that about 3 hectares of the estate were treated with trichogramma cardboard strips during the production of AOC Bourgueil wine (link).
References
