The pink bollworm, Pectinophora gossypiella, is a major pest of cotton. The female moth lays eggs on developing leaves, flowers and bolls. Wherever they hatch, the tiny larvae move into the reproductive parts and start feeding on flowers, and, later, on the lint and seeds, damaging the locule. Since the boll looks undamaged from the outside, the damage escapes detection.
Even repeated sprays of pesticides are useless to control the larvae once they are inside the boll. Moreover, the pest has developed resistance against insecticides as well as cry toxins expressed in Bt cotton plants through genetic engineering methods.
So A G Sreenivas and team at the University of Agricultural Sciences, Raichur, Karnataka turned to a pheromone-based alternative to control the pink bollworm. Pheromones are chemicals released by females so that males can locate them for mating. Pheromones could therefore be used to trap males.
But pheromone traps are not sufficient to bring down the pest menace, and, if their population increases, the cost will be more than that for insecticides.
However, pheromones can be used to trick and confuse males such that they cannot locate females. Disrupting mating will result in no to low numbers of eggs and, hence, less larvae and, therefore, less damage to the crop. The pheromones have no effect on non-target insects and do not impact pollinators that are useful in agriculture.
But the pheromones are highly volatile. To work over a longer duration, the formulation must release the volatiles slowly, steadily and persistently. So the researchers used the pheromones in a wax formulation.
The wax formulation releases the pheromones slowly and, even after 45 days, more than 40 per cent of the original concentration remained in the wax formulation. Moreover, pheromones from the wax formulation are not washed off by rain.
But what is the optimum dosage?
The researchers selected farmers to conduct large-scale field trials on more than 360 acres of cotton crops in Raichur over two years. They used different dosages per acre in fields separated from each other by at least one kilometre.
A dollop of the formulation was applied directly at the axils of the leaf petiole of young plants. Since the effective distance at which the males can sense the pheromones is a little more than two and half metres, the dollops are applied to plants every five metres. Since the formulation releases the pheromones in larger quantities than the female moths can, males in between two source points will be attracted to one dollop or the other, rather than to female moths.
“The application of the formulation was repeated every month for the complete distraction of male moths,” says Dr. A. G. Sreenivas, University of Agricultural Sciences, Raichur.
The researchers found that even a minimum dosage of 500 grams per acre was sufficient to distract male pink bollworm moths. They estimated mating disruption to be 80 to 90 per cent.
In the first year, the treated fields had an average yield of more than 46 quintals per hectare whereas it was less than 25 quintals per hectare in fields where insecticides were used. In the second year, the difference in yield reduced. Economic analysis showed that the benefit accrued is three times the costs.
Cotton farmers should now experiment with this technique to control bollworm infestation, since the wax-based formulation of the pheromones is already being sold in the market.
Crop Protection, 149: 105784 (2021); DOI: 10.1016/j.cropro.2021.105784
Aradhana L Hans
Babasaheb Bhimrao Ambedkar University, Lucknow
- The researchers had funding from a private company with investments in the was formulation. Moreover, one of the authors of the paper is from the company. Though the authors claim no competing financial interests, and the Elsevier journal which published the paper accepts this claim, it is important that farmers themselves test the product and draw their own conclusions.
- Like pharmaceutical industry invests in drug research, agrotech companies invest in agricultural research. What do you think we should do to reduce self interests influencing research results? (Use ‘Leave a Reply’ below).
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