Sterile Insect Technique (SIT) is the application of sterile insects in the wild population thereby eliminating the species from the area. SIT is the alternative method developed due to the increased resistance among the insect pest and also the environmental pollution caused by the insecticide. SIT technique is a kind of Biological control method, where living organisms are used to control the pest. SIT method involves the control of a species by using its own species individuals which are sterile. The first successful application of SIT was in eradication program of Screw worm fly in North America. Screw worm fly is a parasitic fly and its larvae grow on the flesh of warm blooded mammals especially the live stock animals causing huge economical loss in the diary and meat industries. In SIT control program, the sterile males were released in the wild population, where the sterile males competed with the wild males for the females. The females that mated with sterile males develops eggs that lacks the capacity to hatch, in other word develops sterile eggs. This leads to gradual decrease in the wild population and at one point complete elimination of the Screw worm fly population from the infested areas.
SIT method involves sterilization of one particular sex of the species and then releasing them in the nature. Usually the male of the species is chosen for sterilization as the radiation process not only damage cell's DNA but also effects the physiology of the individuals which is very important factor as females have to survive for long duration for egg development and egg laying. Gamma radiations are used for sterilization purpose. The appropriate dose of radiation should be chosen for damaging DNA alone, and not to affect the mating capacity of the males. The SIT program involves raring of the insects in large quantity in lab and sexing the individuals in an appropriate time and sexed individuals are mass irradiated in lab and later released in the nature. The success of the SIT depends on how the irradiated males compete with wild males in mating with females. Usually the sterile males are released in 10:1 ratio of sterile male: wild males for successful control program.
The low dose of radiation causes chromosomal aberrations in the spermatids in males and when such sperms fertilize the egg, the zygote can't develop normally due the presence of damaged DNA from the sperm causing the death of embryo. This results in either reduced number or nil survival from the individual female, thereby decreasing the population. The continues release of same number of sterile/ irradiated males in the nature makes the ratio increasing from initial 10:1 to many fold, and finally it becomes so large that the normal/ wild males will not able to mate any females, there by completely eradicating the insect species from the affected area. SIT technique is not suited for situations of sudden burst of vector populations or vector borne diseases. The first line of control of insect pest is through the application of pesticides to bring down the insect population to below threshold level which can be further controlled with application of sterile males through SIT method, there by completely eradicating the insect species from the area.
SIT method has been applied in several other insect species apart from Screw worm fly. The other species where the SIT was success are Medfly, Mexican fruit fly, Melon fly and Tsetse fly. Several ongoing research of SIT control measures are developed for eradication of Anopheles mosquito, Aedes mosquito, and various species of fruit flies. Though SIT method appears very simple, huge effort is required to develop the correct dose of radiation, raring the insect in large quantities, sexing the individuals for radiation, and transportation of the lab insects for field release. Failure at any one of the stage will results in complete failure of method.
The SIT has minimal side effects on nature and there is no effect on other species in the nature together with less environmental pollution. Hence SIT is target species specific eradication program which affects only the population of interest unlike other insect control program like chemical control etc. This advantage of SIT is very useful and has many promising applications in the eradication of pest populations.
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An enthuiastic author from India