The researchers — Nenita D. Cacayorin, Leonardo T. Pascua, Magdalena C. Damo and Dr. Edison C. Rinen — reported that with a Trichogramma population density of 67,000 a hectare in the field, 58 to 100 percent of the bollworm eggs are parasitized.
In their study, the researchers released Trichogramma pupae and adults in the field when bollworm eggs started to be observed. The adults were released early in the morning, while the pupae were released late in the afternoon.
Aside from parasitizing at least 58 percent of the bollworm eggs in the field where the wasps were released, the insects also spread to the surrounding fields and parasitized 22 percent of the bollworm eggs. Moreover, the presence of other naturally occurring parasitoids also helped in increasing the parasitization rate.
The researchers cautioned, however, that pesticides should not be sprayed on the cotton plants right after releasing the parasitoids as this diminishes the parasitization rate. The immature stages of Trichogramma should be given enough lead time to get into the bollworm so that they could survive pesticide application.
Although the value of Trichogramma as a biocontrol agent is limited by its sensitivity to chemical insecticides, the researchers said this could be addressed with proper insect monitoring and timing of field release.
A higher seed cotton yield and lower cost of bollworm control were attained in areas where Trichogramma was released. Pesticide applications in fields without Trichogramma release were three to four times more than those with the parasitoids, thereby resulting in higher cost of bollworm control and higher cost of producing a kilo of seed cotton.
For three consecutive years, an increase in seed-cotton yield and a reduction in the cost of insecticides as well as labor cost in spraying more than compensated the added cost of producing Trichogramma strips and the labor incurred in releasing the parasitoids.
Moreover, the frequency of spraying was reduced by three to four times. — S.Ma. Pablico