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Taiwan Sugar's Trichogramma egg cards have arrived, but supply is unstable, limited to 200 cards per person

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Farmers, grab them fast! Parasitic wasps are useful but supply is unstable; Taiwan Sugar recently received a shipment of Trichogramma egg cards, limited to 200 cards per person

In nature, when one organism specifically preys on or harms another, we call the latter the natural enemy of the former. Tom Cat chasing Jerry Mouse in the cartoon is one example; the idiom "the mantis stalks the cicada" is another. This natural law of one thing checking another can also be applied to agriculture.

Using natural enemies for biological control can be broadly divided into two types: predatory and parasitic. A predatory example is releasing green lacewings to eat pests, while parasitic wasps are the most common application of the parasitic type. Domestic experiments have found that Trichogramma wasps are very effective against lepidopteran pests such as the Asian corn borer and sugarcane borer; for fall armyworm, they need to be used together with pesticides, which can also achieve the goal of reducing pesticide use.

Trichogramma wasps lay their eggs inside the eggs of the rice moth. (Photo provided by Hsieh Chia-hung)

Parasitic wasps fall into three types: egg parasitoids, pupal parasitoids, and larval parasitoids

Hsieh Chia-hung, associate professor in the Department of Forestry and Nature Conservation at Chinese Culture University, is a domestic expert on parasitic wasps. He says that under the national policy direction of "halving pesticide use," biological control is indeed worth promoting vigorously, as it can reduce pesticide use and environmental pollution without sacrificing the quality or quantity of agricultural products, making it a win-win-win approach for farmers, consumers, and the environment.

Hsieh Chia-hung points out that according to the insect's growth stage, parasitic wasps can be divided into three categories: egg parasitoids, pupal parasitoids, and larval parasitoids. Trichogramma is an egg parasitoid, and its hosts are lepidopteran pests such as the rice moth. After mating, the female Trichogramma wasp lays its eggs inside the eggs of the rice moth. After the wasp eggs hatch into larvae, they eat the contents of the rice moth egg, so the rice moth cannot hatch into a larva.

The dual-spotted ichneumon wasp is a pupal parasitoid, whose main hosts are the rice armyworm and noctuid moths. The female wasp lays her eggs inside the pupae of the armyworm or moth. After hatching, the wasp larvae feed on the tissues of the pupa, thus preventing the pupa from becoming an adult.

As for larval parasitoids such as braconid wasps, they lay their eggs inside the larvae of the diamondback moth or the tobacco cutworm. After hatching, the wasp larvae eat the organs of the larva. Although a parasitized larva does not die immediately and may continue to cause damage for a period, it still helps reduce damage in the field.

Hsieh Chia-hung is a parasitic wasp expert in Taiwan (photo by Yang Yu-yun)

Trichogramma egg parasitoids are as effective as chemical pesticides, but farmers report they cannot buy the egg cards

Hsieh Chia-hung entered the field of parasitic wasp research at the invitation of former Bureau of Animal and Plant Health Inspection and Quarantine Director-General Feng Hai-tung. Feng Hai-tung, who came from an entomology background, wanted to foster the biological control industry. At the time, Taiwan Sugar, which specialized in rearing parasitic wasps, reported that their wasp strains had been domesticated, and the resulting weakening of the stock had caused them to lose their ability to search in the wild and to parasitize, so they hoped researchers could help. Also from an entomology background, Hsieh Chia-hung joined the field of parasitic wasp research at this time.

Hsieh Chia-hung and several other researchers first found many varieties in the field, mixed them into Taiwan Sugar's parasitic wasp strains for improvement, and released the improved strains in simultaneous experiments in Yunlin and Hualien. In Yunlin, the effectiveness of using Trichogramma to control the Asian corn borer was very good, no worse than conventional pesticides; in Hualien, using parasitic wasps alone was not markedly effective, but after halving pesticide use and combining it with Trichogramma, the effect was also comparable to using chemical pesticides alone. This shows that Trichogramma is indeed effective in integrated control of lepidopteran pests such as the Asian corn borer and sugarcane borer.

Unfortunately, such an effective method cannot be used by farmers. Chiayi and Yunlin are Taiwan's main corn-growing areas, and the Asian corn borer is the main pest of corn; when damage is severe, it can cause plants to lodge, resulting in serious yield losses. Although farmers are willing to try parasitic wasps, the egg cards have been out of stock for at least two years. Farmer Kuo Ming-hsien questions this: the government goes to the countryside to promote biological control, yet Taiwan Sugar, the only producer of parasitic wasps, does not supply them. "Do they take farmers for fools?" he asks.

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