The Trichogramma Wasp
Trichogramma are tiny black wasps, almost too small to see with the naked eye. They lay their eggs inside the eggs of corn borers and other moths. When the Trichogramma hatch, they begin to eat the developing caterpillar inside the egg.
A parasitized caterpillar egg becomes black in color as the young wasp develops inside it. After 8-10 days inside the host egg, the young Trichogramma wasp emerges as an adult. The females are then ready to parasitize other moth eggs. A female wasp can parasitize up to 50 moth eggs during its lifetime of 5-14 days.
Use of Trichogramma in Pest Control
The Trichogramma wasp is an effective biological control agent against the Asian corn bore r (Ostrinea furnacalis) and similar pests. The wasps are mass produced in many countries, including the Philippines, for biological pest control. However, it is difficult to produce enough of them to meet farmers' needs. Mass production is the major bottleneck in the large-scale utilization of this useful parasitoid wasp.
To raise Trichogramma requires the eggs of some host, on which the wasp can lay its eggs. When the wasp larvae hatch, they use the eggs of the host as a food source. The rice moth, Corcyra cephalonica, is often used as an alternate host for the mass rearing of Trichogramma. The mass rearing of Trichogramma thus depends on the mass rearing of rice moth, which is quite laborious.
Mass Production of Trichogramma
In 1998, FFTC set up a pilot laboratory in the Philippines at the National Crop Protection Center (NCPC) for the mass production of Trichogramma, using rice moth as the alternate host. The new pilot laboratory used a technique developed at the Corn Research Center in Taiwan, where mass rearing is partly mechanized.
A low-cost prototype egg card machine was made in the Philippines, and after some fine tuning is working well. The machine coats a thin piece of thick paper with a thin layer of glue. Simultaneously, it spreads rice moth eggs evenly over the glued paper.
The egg cards are then irradiated under a UV light, placed in a plastic bag with a card of emerging adult Trichogramma, and distributed to farmers.
Mass Rearing of Rice Moth
At the pilot laboratory, the rearing rooms can accomodate 480 wooden rearing boxes. Each week, the laboratory can supply enough Trichogramma for 150-200 ha of corn fields.
Much of the work of the pilot project has involved adapting rearing techniques to the conditions of the Philippines. For example, the Philippines is a tropical country where temperatures are high. This increases the activity level of the rice moths, and means that some of the adult moths are weak and unable to reproduce.
The laboratory was therefore air-conditioned, and the air temperature monitored to make sure it remained in the range of 26-28oC. Great attention was also paid to good ventilation and hygiene management in the laboratory.
Different species of Trichogramma are being maintained at the laboratory. They are being monitored, to see how they respond to prolonged mass rearing, and also their effectiveness in controlling corn borer in the field.
Using Local Materials to Keep down Costs
To reduce production costs, local materials were used as much as possible. Locally made wooden boxes were used for rearing the rice moths.
The medium was based on high-quality rice bran, and was fumigated before use to prevent infestation with red flour beetle and other unwanted insect species. The target is to produce 7 cc eggs per kilogram of medium, which would mean 70 cc of eggs from each rearing box.
Impact of Trichogramma on Corn Borer
Field releases of Trichogramma in farmers' fields were carried out in the Philippines. The wasps were released three times at weekly intervals, beginning 30 days after planting, at a rate of 70,000 parasitoids/ha. In some fields Trichogramma alone was used, in others the parasitoid was combined with carbofuran and/or the removal of corn tassels.
Monitoring found that in the test fields, more than 75% of the corn-borer egg masses had been parasitized by Trichogramma by the time the corn reached the tasseling stage.
Extending the Technology
The mass production technology and management of Asian corn borer are being extended throughout the Philippines by staff of the regional crop protection centers and local government technicians, who attend three-day training courses at NCPC. The use of Trichogramma to control corn borer is also being shown in television programs. Groups of interested farmers are visiting the Center on their own initiative to learn more about using the wasp in pest control. All over the country, corn growers are becoming aware that Trichogramma wasps are highly effective against Asian corn borer.
Knowledge gained in this project is also being applied to the mass production of Trichogramma chilonis Ishi to control sugarcane borer. Recently, the Philippine Sugar Research Institute established a pilot laboratory on Negros, a major sugar producing island in the central Philippines, with the help of NCPC staff involved in the project. Two more pilot laboratories are to be built on Negros this year.
Index of Images
Figure 1 A Trichogramma Wasp Laying Its Egg Inside a Cornborer Egg
Figure 2 Black Cornborer Egg Mass Parasitized by Trichogramma (Left) beside Healthy Egg Mass (Right)
Figure 3 Corn Stalk Damaged by Cornborer Larvae
Figure 4 Ear of Corn Damaged by Cornborer
Figure 5 Egg Card Machine Built in the Philippines