Dr Lian-Sheng Zang from Guizhou University presented on the Novel Use of Drones for Releasing Trichogramma Parasitoids against Agricultural Pests in China in an ASEAN FAW Action Plan webinar on Drones and Digital IPM .
Dr Zang answered many questions from the audience and in this blog we share his responses. One of the videos related to his work that couldn't be played in the workshop is below and shows the use of drones for releasing Trichogramma against soybean pod borer. The other video can be found on our programme page along with the webinar recording and copy of presentations.
Q1: In general, how many hectares would you need to apply Trichogramma in this way, for this method to be cost-effective?
In my experience, at least 20ha is needed because a one-time departure of the drone can control about 20ha with releasing the Trichogramma. You can also manually release the carriers - for this situation, one person could control pests with the carriers for around 40ha in about 8 hours. In this situation, we evenly release 45 carriers per ha, placing each carrier at about 10 m intervals.
Q2: Can you use any pesticides in conjunction with Trichogramma application – or does it need to be one or the other?
In northeastern China, on most occasions, only the corn borer, rice stem borer and soybean pod borers need to be controlled. For these pests, only releasing the Trichogramma is enough to control them. For some diseases, conventional chemicals also need to be used. When used carefully, they can be used in conjunction with the Trichogramma.
Q3: Does rainfall impact the success of the Trichogramma application?
Yes. We have to release Trichogramma on no rainfall days. The Trichogramma parasitoids are small, less than 1 mm, which are easily impacted by rainfall. And we also can not use drones on rainy days.
Q4: Why are the Trichogramma carriers painted dark colours? What are they made of? How long does it take before they degrade in the environment?
The dark colours are more effective. The carriers are fully biodegradable and are made of corn starch and take about 3 months or less to degrade. They can float in water and the parasitoids can crawl out of the holes at either end. The carriers can have different designs depending on where they are used. The top pictures below show the carrier used in paddy fields, which can float in water. The bottom two photos show carriers used in upland fields.
Q5: What is the size of the carrier? How many eggs are accommodated in one carrier?
For the large eggs of Chinese oak silkworm, about 60 eggs, for small eggs, 3300 to 4000 parasitoids. The carrier size is about 3.5 cm in diameter
Q6: What stage is the Trichogramma at the time of release? It is reported that Trichogramma is not able to reach the bottom layers of the multilayered FAW eggs. What is your experience with the parasitism offered by Trichogramma releases alone on FAW eggs?
We control their development indoors and release them almost at emergence so that they usually emerge within the next day after release. Considering the cost and the potential of Trichogramma dendrolimi parasitizing FAW eggs with different level thickness, it is recommended for large-area release of Trichogramma with drones against FAW that a combination with other dominant natural enemies, such as Telenomus remus are also used.
Q7. What are the advantages of using drones for releasing natural enemies?
There are a number of advantages. These include:
✔ higher efficiency than manual release, particularly suitable for controlling pests across larger areas of single cropland.
✔ saves labour.
✔ release using GPS and drones can be more precise than manual release and improves the biocontrol efficacy.
✔finishing the release in a shorter time helps to ensure that the oviposition peak period of insect pests is not missed.