Why aren’t entomo-pathogenic nematodes registered under the Insecticides Act 1968?

 

Above: Entomopathogenic nematode-Heterorhabditis [courtesy: late Dr S Ganguly] and Below: Steinernema infective stages emerging from Galleria cadavers on the right [credit: Dr. Sharad Mohan] below.

Pesticides are a broad group of chemicals, biologicals and the latter’s products effective against pests which affect crops, animals and human health. These pesticides are classified as insecticides, fungicides, rodenticides, weedicides etc depending upon the target pests. Since these are selective poisons and yet likely to affect environment as well as human health, their use and many other aspects of their production, storage, transport and marketing are regulated under the Insecticides Act 1968. Synthetic pesticides were the first to come under this Act because of their high toxicity and availability. Over the years, ecologically safe biopesticides were developed. And this group included naturally occurring plant extracts, modified natural products, synthetic natural products like pheromones, fermentation products of microbes, pathogens per se as well as natural enemies like parasites and predators. Of the parasites, there are those arthropods that complete the part of their life cycle on the pest insects. There were many of them like Trichogrammatids which feed upon and live inside the eggs of pest insects, braconids feeding inside larvae of the pest insects, and ichneumonids feeding inside the pupal stages of pest insects, until the adults emerge out in open, and again start the next generation after mating and egg laying in the live animal hosts. These are endoparasites unlike the predators that engulf pest insects in any stage in a short time. Insect parasites are essentially parasitoids and not parasites in true sense of its meaning. True parasites are those that complete their life cycle inside host and infect others through various means. True parasites are either obligate meaning they survive only in live hosts or facultative meaning that they can survive on non-living host media. Insect viruses are obligate parasites that multiply in live hosts. On the contrary, entomopathogenic fungi can be multiplied on the non-living feeds [media] and used to parasitize pest insects. 

Entomo-pathogenic nematodes [soft bodied, non-segmented round worms] are mostly obligate parasites that multiply in living hosts and are rarely multiplied on non-living feeds. They are not ecologically independent in the nature like insect parasitoids. And hence, they should be classified as true parasites like pathogens. Entomo-pathogenic nematodes cause pathogenicity due to the presence of symbiotic bacteria, Photorhabdus and Xenorhabdus spp, inside their body, like the pathogenic microbes. Since pathogenic microbes need to be registered as insecticides, entomo-pathogenic nematodes should also need to be registered as insecticides.  

Currently, products based upon four species of entomo-pathogenic nematodes are being sold in the country e.g. greentech [ICAR-NBAIR, Bangaluru], EPN biopesticide formulation [ICAR-SBI, Coimbatore], Pusa-nemagel, Pusa-5SD and others based on some species [ICAR-IARI, New Delhi] and many others of ICAR, SAUs and others in the country. Often, their doses differ a lot and so is the stability of these formulations. In view of these constraints, entomo-pathogenic nematodes are likely to be mis-used by the unscrupulous people for profit motives. Arthropod parasitoids and predators, being ecologically adaptive and partly feeding on live pest insects can continue to be outside the purview of the said Act.