Ecdysteroid insecticides contribute to pest reduction without generating side effects

Advances in agricultural pest management are demanding solutions that combine efficiency, selectivity, and sustainability. Producers are increasingly seeking tools that maintain control of the main caterpillars without compromising the balance of the crop ecosystem.

In this scenario, ecdysteroid insecticides, also known as insect growth regulators (IGRs), play a strategic role.

These products interfere with the molting process (ecdysis), mimicking the insects' natural hormone responsible for this stage of development. The result is efficient and selective control, especially over caterpillars of economically important crops such as soybeans, corn, cotton, and sugarcane.

Mode of action

Ecdysteroid insecticides, such as the active ingredients methoxyfenozide, tebufenozide, and chromafenozide, belong to the diacylhydrazine chemical group. They mimic the action of ecdysone, a hormone responsible for cuticle shedding in the immature stages of insects.

When the caterpillar comes into contact with or ingests the product, the compound binds to hormone receptors and triggers premature and disordered molting. The insect stops feeding almost immediately and, in a short time, dies due to incomplete or malformed ecdysis.

In practice, the producer notices a rapid reduction in crop damage, although visible caterpillar mortality occurs more slowly. This behavior may give the false impression of control failure, but it is the characteristic mode of action of ecdysteroids: the caterpillar simply stops causing damage soon after exposure to the product.

Agronomic advantages

One of the main advantages of this technology lies in its selectivity. Ecdysteroid insecticides are highly specific to lepidopteran pests and have a low impact on natural enemies such as ladybugs, lacewings, and parasitoid wasps. This characteristic makes them valuable tools in Integrated Pest Management (IPM) programs.

Furthermore, because they act through a distinct mode of action, these products help in the rotation of active ingredients, reducing the risk of resistance in pest caterpillar populations. This rotation is increasingly necessary given the intensive use of neurotoxic chemical groups, such as pyrethroids and neonicotinoids.

Another positive aspect is the safety for the applicator and the environment, since diacylhydrazines have low toxicity to mammals, birds, and fish. This characteristic is valued in sustainable production programs and agricultural certifications.

Main pests and crops of use

In the field, ecdysteroid insecticides have demonstrated excellent performance in controlling lepidopteran caterpillars that cause significant damage to Brazilian crops.

In soybeans, they exhibit high effectiveness against the soybean looper (Anticarsia gemmatalis) and the soybean looper (Chrysodeixis includens).

In corn, the main target is the fall armyworm (Spodoptera frugiperda), which is also controlled with good results when the product is applied in the early stages of infestation.

In sugarcane, these products are important against the sugarcane borer (Diatraea saccharalis), and in cotton, they help control Helicoverpa armigera and Alabama argillacea.

Optimal results occur when treatment is applied to young caterpillars in their early instars, a stage when consumption of plant tissue and product ingestion are most intense.

Products available

Among the products registered in Brazil, the following stand out...

• Methoxyfenozide - indicated for various crops, with translaminar action and high selectivity.

• Tebufenozide - mainly used in soybeans, corn, and cotton.

• Chromafenozide - registered for use against various lepidopteran targets.

These products should preferably be applied as soon as the first caterpillars are detected. Late application, when the insects are already at more developed stages, reduces the effectiveness of the control.

Another important point is the uniformity of coverage: since the product acts through contact and ingestion, it is essential that the spray reaches the plant canopy and the feeding surfaces of the caterpillars. The addition of adjuvants can improve the penetration and distribution of the spray solution.

The interval between applications depends on the crop and the level of infestation, but, in general, ecdysteroids have a good residual effect, allowing for longer intervals under low pest pressure conditions.

Resistance management

The isolated and repetitive use of the same chemical group favors the emergence of resistant populations. Therefore, the integration of ecdysteroids into resistance management programs is fundamental.

The recommendation is to alternate the use of these products with insecticides that have other modes of action, avoiding consecutive applications in the same crop season.

The IRAC (Insecticide Resistance Action Committee) classifies ecdysteroids in Group 18 – “ecdysone receptor modulators” – which facilitates their rotation with neurotoxic groups and calcium channel modulators, such as diamides.

This strategy reduces selection pressure and extends the lifespan of molecules available on the market.

Trends and perspectives

In recent years, several studies have demonstrated the potential of using ecdysteroids in combination with biological products based on Bacillus thuringiensis (Bt). This combination can enhance caterpillar control and reduce the overall use of conventional insecticides.

Another trend is the development of more stable, controlled-release formulations, which should increase the product's persistence on the leaf and improve efficiency in adverse weather conditions.

Although the number of active ingredients in this class has not increased significantly, there is a growing interest from the chemical industry in improving the technology, seeking greater potency and cost-effectiveness.

In the long term, ecdysteroids are expected to remain a key tool in sustainable management programs, especially in production systems that value the preservation of natural enemies and the reduction of environmental impact.

Good habits

Several practices are essential for the effective use of ecdysteroids in controlling pests in the field. The main ones are listed below.

• Monitor the crop and begin control measures at the start of the infestation.

• Apply with the correct volume and pressure for good foliar coverage.

• Avoid spraying in strong winds or high temperatures.

• Alternate modes of action within the management program.

• Integrate its use with cultural, biological, and chemical tactics.

• Record and track the history of applications on the property.

These practices are crucial for maintaining efficient control and ensuring a return on investment.

The closing thought

Ecdysteroid insecticides are modern and selective products for controlling caterpillar pests in the country's main agricultural crops. Their differentiated mode of action, low toxicity, and compatibility with natural enemies make them important allies in integrated pest management.

When used judiciously – at the right time and integrated with other tactics – they provide efficient control, environmental safety, and sustainability to agricultural production.

* By Thaís Fagundes Matioli Polisel, Esalq/USP

Article published in issue 320 of Cultivar Grandes Culturas Magazine