The incredible and Amazing Nematodes as alternatives to Pesticides
By Aashaq Hussain Bhat
The pest problems on vegetables and other incredible crops has been observed to be very serious in certain parts of Kashmir valley and they have been found to be monophagous, oligophagous or polyphagous based on the number of host plants preferred. The insect pests of vegetable crops either inflict direct damage by biting the tissues or sucking sap from them or indirectly by wounding of tissues resulting in lesions through which disease causing organisms’ viz. bacteria and fungi enter. The pests may also help in transmission of diseases from one host plant to another. Crop losses due to pests are higher for this region than for other parts of the world (APO, 1993). Out of various constrains, insect pests of vegetables and fruit crops in Kashmir, play an important role in lowering the yield and is the biggest challenge that confronts our agriculture sector today.
Presently the surge of production of horticultural crops is increasing day by day due to indiscriminate, unfettered, nonjudicious and rampant use of chemical pesticides and fertilizers and without their use , it is very likely that pests would consume higher percentage and cause huge losses to productivity. Pesticides play a pivotal role in boosting the agricultural productivity by increasing production and profits of farmers and also prevention of diseases. But at the same time, these pesticides are deteriorating all spheres viz. lithosphere, hydrosphere, atmosphere and biosphere and have resulted in serious implications to man and environment. They are taking a heavy toll on our environment and human health thereby losing the purity of environment, poisonings and development of cancer in humans, deaths, bioaccumulation and biological magnification etc and harm non-target organisms. A recent World Bank report assess that 3,55,000 people worldwide die each year from unintentional pesticide poisoning and cancer problems are increasing in valley from past few years which are directly or indirectly linked to pesticide poisoning.
With the use and also with the production of pesticides are associated a large number of hazardous high risks and alternative measures are therefore mandatory to get rid of these consequences and save this planet earth. In the present scenario, developing countries are intended to increase the awareness and to enhance the better understanding of naturally occurring beneficial microorganisms in the terrestrial environment. One of the beneficial control agents paying attention of experts worldwide is the use of entomopathogenic nematodes (EPN). These are microscopic organisms residing in the soil and cause death of insects which come in contact with them but are not lethal to non-target hosts including humans and other vertebrates. Actually only their 3rd stages which are infective stages called infective juveniles (IJ) are found living freely in the soil (all other stages only develop inside the host body) and locate their host in soil by means of two strategies-sit and watch behaviour (ambushing and cruising) like that of crocodiles. Once they come in contact with their host i.e., larvae of insect, they jump on them and penetrate their body either through their natural openings or by abrading their cuticle. They employ different foraging strategies to locate and infect hosts. The IJ are associated with bacteria which reside in their alimentary and live in mutualistic association with them and it is this nematode bacterium complex that works together as a biological control unit to kill insect hosts within 24-48 hours by penetrating the host through different pathways and thereby releasing the bacterial symbiont which spread and multiply in the haemolymph of the insect pest and kill them by septicaemia. They have been tested experimentally worldwide as non-lethal to humans and other vertebrates and invertebrates expect entomic fauna. It has been proven that these IJ locate their insect host via some chemical secretions by insect body which are sensed by nematode body and thus are only parasitoids only to them.
In several countries, EPN are utilised as effective biopesticides as they can be incorporated in IPM programs being non-toxic to humans and other vertebrates, relatively specific to their target pests and can be applied with standard pesticide equipment. EPN have proven to be the most effective as biological control organisms with significant results. Entomopathogenic nematodes have been released extensively in crop fields with negligible effects on non target organisms and are regarded as exceptionally safe to the environment. IJ of EPN have been proved to be not harmful to humans and other vertebrates, can be easily mass-produced using conventional fermentation technology, and several formulations of EPN are available in the market for the control of cryptic pests. In this high opinion about EPN, the isolation of native species and or abundance provides a valuable resource not only from a biodiversity perspective but also from a more applicable stand point. Indigenous EPNs may result more suitable for inundative release against local insect pest because of adaptation to local climate and other population regulators. In addition many countries are concerned about the introduction of exotic EPN because they may have negative impact on non target organisms.
Till date several species of EPN have been reported worldwide and they fall under two families: Steinernematidae represented by the genera Steinernema (more than 100 species known globally) and Neosteinernema (only 1 species) and Heterorhabditidae represented by the genus Heterorhabditis (more than 20 species). The IJ of Steinernema are associated with mutualistic bacteria in the genus Xenorhabdus and that of Photorhabdus for Heterorhabditis. The IJ of Steinernema and Heterorhabditis are used as control agents against diverse insect pests. Sixteen species of EPN have reported in India till date and still others are waiting for their discovery. This is due to lack of taxonomic specialists in the field of nematology and thereby providing a plenty of room for studying these fascinating, useful and delightful worms and later to implement them as biopestcides.
Several EPN are used worldwide as biocontrol agents under different trade names viz. Ecomask, Savoir Weevil larvae, Guardian, J-3 Max, Heteromask, Lawn Patrol, Scanmask, Entonem, Nemasys etc and have provided excellent results against different entomic fauna. In United Kingdom, Bionema Company is commercially producing formulations of EPN so as use them in biological control of different pests and earns corers of US dollars every year. In India, few EPN species have been exported from developed countries several years ago to exploit them as biopestcides but failed as they could not acclimatise to conditions here. Therefore the best approach is to make use of indigenous species existing locally and they will provide outstanding results. Little work on EPN as bio-insecticide has been done in India and till now only one species of Steinernema, viz. S. thermophilum synonymised as S. abbasi has been patented by IARI, New Delhi and is annually given to company for crores. This was isolated from West Bengal and is therefore, widely exercised in west Bengal for controlling different quarantine pests of sugarcane and other crops being a native of that place. But as far as valley Kashmir is concerned, still no work has been done for isolating indigenous strains of EPN and later implementing them as biopesticides. Therefore, the need is to do extensive survey of different horticultural, forest and agro fields for getting local isolates and later mass culture them so as to utilise them as biocontrol agents for sustainable agriculture and protect the paradise on Earth from the perilous and unsafe use of hazardous pesticides which will ruin the valley with coming years if used at such alarming rate. The researchers of Kashmir valley should focus on getting effective strains of indigenous EPN and later implement them in agronomy and horticulture by mass culturing them in in vitro and in vivo techniques for betterment of environment and healthy life.
The author is DST Inspire Scholar at Chaudhary Charan Singh University, Meerut (UP)