Savant confirms Bt eggplant's durability

Pest-specific toxins reduce losses for farmers

A former UP Los Banos professor says the battle against plant pests is a continuing one but confirms that biotech corn and eggplant offer the best chances to paralyze pests and deny them sanctuary in farms.

Dr. Emiliana N. Bernardo, who chairs  the Insect Resistance Management Advisory Team of the Department of Agriculture (DA-IRMAT), stressed that insect resistance "is the ability of insect pests to overcome the defense mechanisms of their host plants and succeed in infesting them."

Bernardo said  the most desirable and effective way to battle pests is to introduce genetic material in crops that produce toxins that target the pests but would not pose any risk to human.

Bacillus thuringiensis (Bt) corn and Bt eggplant possess this ability to cause "high mortality of the pest" as they feed on the resistant corn and eggplant.

By reducing the pest population, Bt corn and Bt eggplant farms are assured of higher yields.

Work on Bt eggplant's resistance is being undertaken in several sites nationwide but initial results showed that the plant has barred the influx of pests that bore deep into the fruit.

The reason for this is that Bt eggplant produces toxins on the skin that are completely offensive to the borers and fatal those that try to pierce the skin before burrowing deep into the fruit.

Bernardo said the defense mechanisms of host plants can be genetic or heritable and is referred to as host plant resistance (HPR) , as in the case of the  genetically modified insect resistant Bt corn (MON 810.)

They may also be temporary and thus not heritable as in the cases of vegetables or crops protected by insecticide.

Insect resistance management (IRM), explained Bernardo, requires the application of a strategy that detects the level of resistance by the pest and tactics that would reduce the pest population and thus substantially reduce its damage to crops.

IRM demands a keen understanding of the pests, their life cycles and how they can be eradicated using their natural enemies in the field, and the crops as well, particularly how they can reduce the stimuli for pests to inhabit them and even their genetic armaments to combat infestation.

In the case of heritable HPR, Bernardo noted some plants are "non-preferred" by pests owing to their being hostile to the propagation of the pests, since they have features not conducive to the deposition of eggs, or even emit chemicals offensive to the pests.

"It has been observed that corn ears with thick, more tightly pacl husks extending well beyond the corn cob tip usually incur minimal corn earworm damage," she noted.

Some crops are also tolerant and would not succumb to infestation since they can replace the parts upon which the pests feed, meaning they can regrow, just like tolerant  strains of rice that produce more tillers to replace the damage ones called "dead hearts."

An important HPR property is antibiosis, which means that pests would suffer if they feed on the resistant plant, and would be subject to lengthened developmental period or life cycle, smaller body size or "reduced fecundity of essential food nutrients derived from the resistant host crop."

Bernardo admits that since the time Bt corn was commercialized in the country in 2002, there has been no report of populations of Asian corn borers (ACB) that have shown immunity from the genetic weapon of Bt corn.

Instead of feeding on Bt corn, the ACB instead shift to other corn varieties planted near Bt stands that are cultivated to test just how effective the biotech crop is in combating ACB. 

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