Diamond moth killer
Sex attractant reduces need for pesticide

By Helen Chan

Mr. Lau Siu-ki, an agricultural officer of the Agricultural and Fisheries Department, said, “With the use of sex attractants, farmers can know about the migration of diamond moths. Then, a pesticide can be applied accordingly.”

The sex attractant is composed of pheromone, a hormone secreted by female diamond moths. It can attract male diamond moths. It is put into several yellow basins, which are fixed up with steel wires by farmers.

Said Mr. Lau, “Yellow colour is preferred because it attracts various insects, including diamond moths.

“Actually, adult diamond moths will do no damage to the crops. This new method mainly targets at larvae of the diamond moths.”

The larvae, which are hatched from the eggs laid by female adult diamond moths, will eat up the crops within a few days. By killing the male adult moths, the number of larvae can be reduced.

“To avoid insects attracted by the sex attractant without being drowned by the water, detergent is added to the water so that the moths can no longer fly once they drop into the water,” Mr. Lau said.

Farmers need to check the number of male diamond moths attracted in the basins to see if the tally increases drastically. If the number exceeds 20 a day, that means there are some diamond moths on the farm.

The most appropriate day for applying pesticide is chosen according to the average temperature of the day.

“With an average temperature of 18 degrees Celsius, the larvae will be developed after 9 days.

“The new larvae are most sensitive to pesticide. Therefore, we should apply pesticide 9 days after about 20 adult moths are attracted in the basin,” Mr. Lau said.

Without this method, farmers are forced to apply pesticide for a fixed period of time. However, not only does it waste the farmer’s money, it also induces the problem of pesticide resistance.

Mr. Lau said that the larvae may develop resistance to the type of pesticide used by farmers if they are frequently exposed to it.

Therefore, besides minimizing the damage to vegetables, using this new method to forecast and kill diamond moths is said to be able to lessen pesticide resistance to crops.

Officers from the Agricultural and Fisheries Department are responsible for supervising the technique if farmers are willing to participate in the pilot scheme of this new method.

Some farmers in Ho Sheung Heung have been selected to adopt this means in their farms.

Mr. Wong Ping-sum, 44, is among those who are willing to use this method to eliminate diamond moths. He started using this method more than two months ago, and he found it effective.

Said Mr. Wong: “Detailed explanation was given to me before the experiment began.

“The officers from the Agricultural and Fisheries Department would inform me whenever I need to apply pesticide.

“This method should be promoted to other farmers so that they are able to grow crops at a lower cost.”

However, Mr. Lau pointed out that the farming cost would not be significantly reduced if the farmers are cultivating crops where the growing period is short, since only crops with longer growing period need to be applied with pesticide frequently.

Said Mr. Lau: “The Agricultural and Fisheries Department is planning to introduce this new method of killing diamond moths to all the farmers in Hong Kong.

“However, we need to resolve some technical problems, like educating the farmers, before our large-scale publicity can take effect.

“We are confident that other farmers will follow suit since this method can save much of the money spent on buying pesticide,” said Mr. Lau.

February 1996