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Sterilization – A green technique in infestation control

There are many eco-friendly techniques that are used now-a-days for pest management. The integrated pest management, mating disruption, mass trapping with sex or aggregate pheromones, use of biological predators, use of insect growth regulators, use of desiccants are some of the known, tried and tested techniques which are eco-friendly and green.

“One factor is common in these treatments – they employ the principles of biological warfare using germs, sterilization and other biological weapons. These techniques are expensive. Green techniques involve an extensive and comprehensive approach in pest control and include a combination of different methods. Developing green techniques also involves extensive research and this may be one of the reasons for the cost escalation,” says Sandeep Nijasure, Business Development Manager of Pest Control India.

The core purpose behind the biological treatment despite it being expensive is to sidetrack the use of DDT (dichlorodiphenyltrichloroethane). DDT was one of the most powerful weapons that man has ever invented to wipe out the pest population from this planet. In the 1970s, the US government had banned the use of DDT, but in India, it was used till the late 90s and early 2000. Nonetheless, in 2006, WHO has allowed use of DDT for indoor residual spray in endemic areas.
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Solutions for Termites

Termise is a new generation non-repellent termiticide from Diversey India Pvt Ltd. The termiticide creates non-repellent chemical region, which the foraging termites cannot detect and get exposed. On contact with Termise, the termites become dysfunctional and continue to interact with other colony mates. In the process, they transfer Termise to other termites, intoxicating the entire colony.

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During this time, American entomologist Dr Raymond C Bushland and Dr Edward F Knipling explored a new method, Sterile Insect Technique (SIT). The SIT is defined as a ‘method of pest control using wide inundated releases of sterile insects to reduce reproduction of the population of a species’. It is a birth control technique, as the female pest mates only once a lifetime. In this process, the wild female pest population cannot reproduce when they are inseminated by the radiation-sterilized male pests.

SIT involves three basic stages:

• Rearing pests
• Sterilization of reared pests
• Release of these pests

All these reared sterilized pests are collected and transported under bio-secure methods and treated with Gamma radiation. The radiation dosage is very low, but still effective for sterilization. Pests do not become radioactive in any way that could be harmful to other living organisms. “Gamma rays are very penetrating in nature with lightening speed and hence sterilization purpose requires expertise in operation. It involves use of radioisotopes and can be carcinogenic in nature. Gamma rays travel at the speed of light and exist only as long as they have energy. Their existence ceases once their energy is spent,” explains Nijasure.
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Termites chew up र 10 million
Alarmed over the sudden infestation of termites which has chewed up currency notes worth Rs10 million stored in a bank strong room in Northern India, the State Bank of India has urged other banks to go on a cleanliness drive. Lack of cleanliness and attention has been cited as the cause for this huge loss of money. It has been reported that the Barabanki branch of the bank had been facing termite problems earlier and despite warnings no action had been taken. The State Bank has now warned its staff to regularly clean the premises to keep this new money eating monster at bay.

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The sterilization is done by skilled and certified staff in the laboratory. It is essential that the sterilized pests have a normal mating behaviour so that they can be released in the environment to mate with the wild pest. There is a system that is designed to sterilize pests using a tool called Dosimeter. This is used to ensure that the chosen dose, as decided by the scientist, is achieved in each treatment. The pests that are sterilized are released within 24 to 48 hours. As these pests are reared, the diet fed to the larvae is red, so they grow up taking on this characteristic and this helps to distinguish them from the wild pests. This enables to trap them and get them back to the lab.

Before the pests are released, the process involves evaluation of the location, time of release, method of release, number of insects and the method to measure the effectiveness. If the evaluation is on a small scale, the sterile pest is released by hand. Another option is ground release which is done by trucks. And, when a large area is identified, aircrafts are used for this programme.

There is also limitation to the number of pests that can be released in an area. There has to be a realistic release at one time. Even though there can be multiple releases in a week, this reduces the density of the pest population by the end of the season. The traps are monitored around the release area to evaluate the SIT program. The traps determine the size of the pest population and pest movement as to how far they go and in which direction they travel. This information helps to refine the SIT programme structure. The main goal is to reduce the wild pest population.

There are four strategic options in which the sterile insect is deployed as a component of AW-IPM (area wise-integrated pest management) for pest control:

• Eradication: SIT helps to effectively eradicate the pest population and providing an ecological balance. The target has to be isolated for eradication process, and isolation can be created by using the natural barriers. The technique should be applied on an area-wise basis.

• Prevention: Sterile pests can be released into an area on a regular basis to prevent the establishment of exotic pests. The release can be done in any situation; it is generally carried out where the risk of invasion is high and isolation activities are not sufficient to prevent the invasion.

• Containment: Containment programmes use barriers of sterile insects to prevent the spread of exotic invasive pests that have become established. Some of these programmes become permanent and stationary but others advance, or retreat and eventually disappear.

• Suppression: The benefit of using the sterile pests within integrated suppression to replace the use of pesticide is gaining increasing acceptance as the cost of sterile pests is decreasing and environmental safety is increasing.

One may think this technique of pest sterilization is actually like challenging the Mother Nature and it can be harmful. Nijasure says, “There are many methods of insect control where we challenge Mother Nature and they are a bit successful in controlling insects like mating disruption, mass trapping of insects with sex pheromones, etc. The success of any method of pest control largely depends upon many factors. That is why the concept of Integrated Pest Management has gained importance where more than one method of pest control are clubbed together for getting the desired results.”

Under the International Standard for Phytosanitary Measures, No. 3 of International Plant Protection Convention established in 1952, sterile insects are categorised as beneficial organism as the SIT is amongst the most environment-friendly insect pest control method ever developed, as the mating cycle is disrupted. The population decreases immensely and SIT does not introduce exotic species into an ecosystem and the experts say “these sterile pests are not harmful to animals and man”.

“In fact, this technique is useful only for those insects where females mate once in life time and have short lifecycle. It is extremely costly, time consuming and laborious considering the process of rearing or trapping of large quantity of insects in a lab and then sterilizing them with gamma rays.

In the case of some of the insects where female mates only once and then she lays eggs for her lifetime like termites, SIT may not work well in this case. We may not be aware of the exact number of the male insects in a certain periphery and the success of SIT mostly depends upon the probability of males sterilized by gamma rays mating the females. May be, the area has many more large number of male insects than what has been estimated for release of gamma ray sterilized males. Most of the insects are flying and some adults may fly from adjoining areas to nullify the effect of SIT,” adds Nijasure. “As per my knowledge, nobody in India is using the sterilization technique for mosquito’s control. May be some scientists are using this technique only for research purpose.”

Scientists at the Mosquito Research and Control Unit (MRCU) have explored a ground-breaking strategy that will hopefully eradicate the dengue fever carrier – the aedes aegypti mosquito, using genetically modified mosquitoes for dengue control in the Cayman Islands (Green Antilles October 8, 2010).

Anjna Nambiar

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