During the nineteenth century, botanical oil sprays

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1 Botanical Oils Foe of Pests, Friend of Farmers By Ravi V and Bharathy P V Botanical oils have been used for cosmetics, lubricants and energy sources for thousands of years. But following talks of synthetic insecticides affecting human health adversely, botanical oils are once again being looked upon as a safer alternative to pesticides During the nineteenth century, botanical oil sprays were reported to control scale insects and research ers showed that botanical oils were effective plant protectants. In the 1920s, several researchers showed that sprays of botanical oils killed aphids and scale insects. These oils were not widely used as pesticides because of the development of synthetic insecticides and more uniform petroleum derived oil formulations. However, recent reports of negative environmental and health impacts of synthetic insecticides and increasingly stringent government regulations of pesticides have generated renewed interest in botanical oils. Botanical oils have been shown to kill the eggs of mites and several insect species. Furthermore, more recent research has shown that botanical oils may repel some insects. Since the 1940s, improvements in processing technology have continued to improve oil quality by reducing the concentrations of free fatty acids, phosphatides, iron peroxides and undesirable odors. In the last decade, researchers have shown that botanical oils are not only effective as emulsifiers of pesticides, but also they are themselves effective pesticides. One of the factors limiting the use of botanical as pesticides is the variability in oil composition and the absence of well-defined standards for pesticidal usage. In 2002, approximately 100 million tonnes of oils and fats were produced worldwide, of which 85 per cent was of botanical origin and 15 per cent of animal origin. The most abundant botanical oils produced world wide were soybean-24 per cent, oil palm- 23 per cent, canola-14 per cent, sunflower-9 per cent, peanut-4 per cent, cotton seed-4 per cent, coconut-3 per cent, olive-2 per cent. According to European Oleochemcials and Allied Products Group (2001), majority of the plant derived oils were produced from North and South America, Argentina, tropical countries of Pacific Rim, Canada, European countries, Scandinavia, Japan and US pacific coast. Plant oils are derived primarily from seeds. There is considerable variation among species in oil content and storage tissue within the seed. Oils can be stored in the endosperm (coconut, castor and bean), the cotyledon (peanut and soybean), and the scutellum (maize) and in the fruit pulp tissue (olive and palm oil). Soybean oil is the most abundant oil used and thus offers the most promise as a pesticide, because of its economical and readily available. Criteria for selecting plant spray oils Modern plant spray oils needed quite specialized traits to be acceptable for use in diverse pest control situations. Physical considerations Recommended oils are characterized by their viscosity, gravity, unsulfonated residue (UR), pour point and distillation temperature (50 per cent and per cent range). Narrow-distillation-range products are desirable for both plant safety and pesticidal efficiency. Gas chromatography should be used to improve the precision of older ASTM distillation methods which allow tolerance limits in the distillation that are too wide. Chemical considerations Aromatic and other unsaturated hydrocarbons should be as low as possible (preferably < 8 per cent). Suitable verdant plant oils can be selected from fractions having an average molecular weight of approximately , with those on the lighter end better suited for use on mole sensitive plant species. An oils mechanism of action in killing pests should involve in the normal gaseous exchange of the pests respiration. However, the ideal formulation of a plant oil to be used as a pesticide should be a relatively long-lived emulsion without excessive shaking forms small droplets that disperse and spread rapidly over leaf and stem surfaces relatively stable in the environment and does not change properties rapidly with environmental fluctuations and the emulsion breaks easily in the plant surface, leaving the oil film on the plant and letting the water roll off 1

2 Some of the important oils used in controlling pests Vegetable oils Soybean Cotton seed, Peanut Linseed oils Chrysanthemum Carnation Enconyms Dogwood Sweet pea Oak Geranium Sweetgum Pine Pear Sycamole Mexican bean weevils on stored beans Flat grain borer on maize Lesser grain borer on sorghum Mosquito larva Eggs of grape berry moth Sweet potato whitefly on cotton Whiteflies, Mites Mites Scales, Aphids Whiteflies, Mites Leaf roller Mites Psyllids Lacebugs Plants suitable for oils Chrysanthemum, Jojoba, Karanj, Pongam, Kokum butter, mahua, Citronella, Lemongrass, Mustard, Neem, Peanut, Rapeseed, Corn, Cotton, Taramira, Rubber, Safflower, Sesame, Soybean, Undi, Wormwood etc. Containing volatile compounds that are toxic and act as fumigants Phytotoxicity on plants Symptoms of spray-oil-induced phytotoxicity are either acute or chronic and usually occur as an extension of a plants' response to concurrent physical, chemical or biological stresses. Oil-induced stresses associated with membrane disruption or by suppression of plant function owing to the physical presence of oil. Oil-induced phytotoxicity can be caused by two different actions: (1) a transient suppression of metabolic functions, in which severity and duration vary with dose rate and distillation properties and (2) membrane disruption, which is a consequence of spray oil component toxicology and relationships between dose rate and plant physiology. However, umbelliferous species such as carrot and parsnip are especially resistant to oils with respect to acute symptoms. Susceptible plants may show the following symptoms in response to higher doses of oils. Slight leaf necrosis Leaf mottling Moderate to severe growth inhibition Water-soaked appearance How do they work? Plant derived oils kill susceptible insects and mites and their eggs by contact. The mode of action is thought to be primarily by suffocation, with death occurring within 24hr. Sprays used primarily to down insects or mites are generally only effective against individual present at the time of application. However, it is becoming increasingly apparent that oils deposits can significantly reduce feeding and oviposition by a range of arthropod pests of plants. According to whether it was being applied to eggs or motile forms, they will be working in different ways. When used as ovicides Oils will prevent the normal exchange of gasses through the outer coating Hardening the outer covering so as to prevent hatching Interfering with the water balance of the eggs Softening or dissolving the outer covering of the eggs, through inference with normal embryonic development Penetrating the egg and coagulating the protoplasm or interfering with enzyme or hormone activity Exerting a negative effect on the insects delicate integument When used on adults Blocking spiracles, thus leading to suffocation Penetrating the tissue in the liquid phase and corroding it by breaking down tissue structure Advantages over synthetics Plant based oils have certain advantages over synthetic pesticides such as Highly refined paraffinic oils are biorational products that are ideal for use in sustainable pest and disease management. They are non-toxic to vertebrates and non-target invertebrates and are therefore safe to use They are generally non-disruptive to natural enemies of pests and beneficial arthropods In many instances they are more effective than synthetic pesticides and When used as a carrier or adjuvant with pesticides they may contribute directly to pest control Future outlook Around the world, continues to show that plant based oils can play a significant role in an IPM approach to agriculture and horticulture. Research is needed to determine the best oil fractions to use and the best emulsion system for various botanical oils. The key properties of plant oils and more recent research must be optimised to ensure good control of the pests being treated while at the same time reducing the risk of acute and chronic phytotoxicity. So, there is a major need for research on the formulation of botanical oils for specific purposes. The proper use of quality botanical oils can result in lower pest control costs and higher crop yields. 2

3 Entomopathogenic Nematodes A Potential Future Microbial Biopesticide By Dr. Mahaveer P Sharma, Dr. S. S. Hussaini & Dr. Alok Adholeya* ALTERNATIVES Free-living species are abundant, including nematodes that feed on insects, bacteria, fungi and other nematodes. A certain group of nematodes that feed on insects by entering the insect body, releasing a lethal bacterium and reproducing in the insect cadaver are called entomopathogenic nematodes with a potential to be treated as a living biopesticide Biological control exploits insects, fungi, bacteria, viruses and nematodes as biological insecticides. Nematodes are the most numerous multicellular animals on earth. These simple colorless, unsegmented roundworms may be free-living, predaceous, or parasitic. The parasitic species cause important diseases of plants, animals and humans. There are nearly 20,000 described species classified in the phylum Nematoda. It has been estimated that half tablespoon of soil will have a numbers of organisms bacteria , actinomycetes , fungi , microalgae , protozoa , nematodes , other invertebrates Freeliving species are abundant, including nematodes that feed on insects, bacteria, fungi and other nematodes, yet the vast majority of species encountered are poorly understood biologically. A certain group of nematodes that feed on insects by entering the insect body, releasing a lethal bacterium and reproducing in the insect cadaver are called insect pathogenic or entomopathogenic nematodes (EPNs). EPN comprises two words, i.e. Entomo- = insect or pathogenic = producing disease. Nematodes associated with insects are referred to as entomophilic, entomogenous or entomopathogenic are known to parasitize, cause disease and kill the insects. There is growing interest in EPN globally mainly because of potential efficiency and other impressive attributes for utilizing against the control of soil-dwelling pests. EPN types and mode of action There are two genera, Steinernema and Heterorhabditis, belonging to families Steinernematidae and Heterorhabditidae, respectively and are highly virulent because of their symbiotic association with bacteria Xenorhabdus and Photorhabdus sp. So far, more than 30 species of these genera have been described out of which nine species of Steinernema and three of Heterorhabditis have been commercially exploited. Unique to EPN is their close association with specific bacteria of the genera Xenorhabdus with Steinernema and Photorhabdus sp. with Heterorhabditis. These bacteria are symbiotically associated with EPN, which they serve as vectors for bacteria, achieve a quick kill of the target insect pests and are safe to vertebrates and humans. These bacterial symbionts belong to the Enterobacteriaceae within the gamma sub division of the purple bacteria. The EPN naturally associated with specific bacteria are found as free-living in the soil, where they are in a nonfeeding juvenile stage. Some species move through the soil in search of a fresh insect larva, while others wait for a larva to crawl by them. Nematodes enter the insect larva through the insect s natural openings: mouth, anus, spiracles (breathing pores) and some species of EPN have teeth with which they can break through the insect s hard cuticle and enter directly into the 3

4 interior of the insect. Regardless of how they get into the insect, the nematodes make their way to the hemocoel of the insect. The hemocoel is the body cavity where the insect s organs are bathed in hemolymph, the blood of insects. The EPN, while capable of being harmful to insects, enjoy a beneficial relationship with the associated bacteria. The non-feeding juvenile nematodes carrying the specific bacterium release it in the hemolymph which kills the insect larva through septicemia. In the days following infection, the bacteria break down the insect into its molecular components so that they and the nematode can feed and multiply. The nematode s life cycle includes an adult stage, an egg stage, and juvenile stages. When the nematode and bacteria begin to run out of usable nutrients in the insect, the bacteria again take up residence in the nematode, the nematode stops growing at a non-feeding juvenile stage and the nematode-bacteria pair leaves the insect carcass. Comparative advantages over other biopesticides Although EPN are extraordinarily lethal to many important soil insect pests, yet safe for plants and animals. This high degree of safety means that unlike chemicals, or even Bacillus thuringiensis, nematode applications do not require masks or other safety equipment; and re-entry time, residues, groundwater contamination, chemical trespass, and pollinators are not issues. Most biologicals require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, kill insects in hours. EPN are highly virulent, possess chemoreceptors to search out their hosts and can be cultured easily under in-vivo and in-vitro. Nematode production is easily accomplished for many species. EPNs are safe to vertebrates, plants and non-targets, have been exempt from pesticide registration in the USA, are easily applied using standard application equipment, are compatible with many chemical pesticides, and are amenable to genetic selection. Nematodes are compatible with standard agrochemical equipment including pressurized, mist, electrostatic, fan, and aerial sprayers. Application through irrigation systems has improved grower acceptance. Insecticidal nematodes are virtually without competition from other biological agents for control of soilinhabiting and plant-boring insects and cost of application equals that of chemicals. How to produce EPN EPN can be isolated baiting soil samples with a living insect larva, which is widely adopted throughout the World. The symbiotic association of entomopathogenic nematodes with specific bacteria facilitates rapid production of nematodes (bacteria serve as food) and successful pathogenicity, though axenic nematodes (nematodes without bacteria) require great deal of work to ensure host survival and reproducibility. Furthermore, bacteria alone are not capable of penetrating the gut and cannot independently gain entry to the host s hemocoel. Thus, nematodes act as vectors to transport bacteria into host within which they can proliferate, and bacteria create conditions necessary for establishment and reproduction within the insect cadaver. A key factor in the success of EPN as biopesticides is their amenability to mass production. EPNs can be mass produced using in vivo and in vitro solid and liquid culture methods. In the in vivo process, an insect serves as a bioreactor; in the in vitro process, artificial media are used. Field application Sprinkling infective juveniles directly onto the soil surface is the most common method. A spray volume of L/ha is usually sufficient for most nematode species to reach the target insects in soil. Nematodes can be applied with nearly all commercially available ground or aerial spray equipments. They can also be applied using drip and sprinkler irrigation systems and pressures of up to 1068 kpa. Best results obtained when applied after the fields/area are lightly irrigated. Foliar application requires to control insect pests on the foliage requires considerable efforts, because of rapid desiccation due to wind and solar UV radiation, which creates inefficiency of EPNs to stay on the site. However, under favourable conditions, i.e. high humidity and calm atmosphere, EPN are very effective against foliar pests. The addition of anti-desiccants and UV protectants to nematode suspensions has improved the efficiency of EPN to control foliar insect pests in most cases. EPN can be 4

5 also be applied as IPM method to control insects of trap crops and can also been used successfully in traps designed to lure and kill insects, particularly for those with sit and wait foraging strategy. Shelf life Steinernematid IJs are stored for extended period of one year under cool, moist conditions. For industrial storage, the IJs are placed onto clean, crumbed polyether-polyurethane million per 100g of dry sponge and maintained at 1-2 C in aerated polyurethane tubes. During transportation, for trips less than 12 hrs, oxygen is added to the tubes before transport. For longer transport the tubes are aerated with a battery operated air pump. The heterorhabditid IJ are best stored in culture flask above 12 C. Shelf life is predicted from storage energy reserves (fatty acids and lipids) of IJs correlated with the type of diet used for production whereas virulence potential is measured using 1:1 bioassay against wax moth. Status of EPN research and commercialisation Field demonstration of EPN has dominated in the western countries covering thousands hectares of land particular reference to Florida citrus Industry. Many pests of horticulture, agriculture, home, and garden besides public health are controlled and EPN have reached the second position after Bacillus thuringiensis based products. In India the Project Directorate of Biological Control, Bangalore, undertook extensive and systematic surveys for determining the existence of several potential native isolates of Steinernema and Heterorhabditis. Significant amount of work on EPN research on selection of improved strains, mass production and developing their simple ready-to-use formulations is being carried out at PDBC, Bangalore. The division of Nematology at IARI New Delhi is involved in the biosystematics of EPN. Several other institutes, including Sugarcane Breeding Institute, Coimbatore, State Agricultural Universities and Energy and Resources Institute (TERI), New Delhi are also involved in EPN research. In the world, the most dominant work on EPN has been carried out in the US, Israel, Germany and the UK, besides some other parts of Europe. A large number of companies are in the commercial production of EPN. In USA, Steinernema carpocapsae EPN is being used against large number of pests belonging to Coleoptera, Lepidoptera and Diptera etc., those of white grubs, mole crickets, fungus gnats, root weevils, bugs borers on variety of crop plants and turfs. In UK, black vine weevil, strawberry root weevil are being controlled by S.carpocapsae, S. riobrave and Heterorhabditis sp. Four nematode species viz., S.carpocapsae, S. riobrave,s. feltiae and H. bacteriophora are nematode industries success stories. Differences in the field efficacy for the two EPN Steinernema and Heterorhabditis were validated, Steinernema was found to be more effective against mole crickets whereas the latter was found very effective against white grubs. Apart from insect pests, other organisms causing diseases to plants, such as plant parasitic nematodes and mites, are being controlled by EPN. Besides, they hold promise against household pests, sucking pests and those of public and veterinary significance. Till date not a single company is producing EPN in India. Most of EPN producing companies are located in the western world. The ease of use of nematode products is constantly being improved through formulation research. The quality of the nematodes that survive the rigors of the manufacturing process is analyzed by determining their shelf life and virulence. Nematode s shelf life is predicted from storage of energy lipid reserves of the infective juvenile nematodes; virulence is being assessed using insect bioassays. Future Directions India being a megadiversity country, there is a need to document the EPN fauna and build up a repository E x t e n s i v e Pathogenicity tests to evaluate local strains against local pest problems and identify the most potential strains Mass production technologies suitable for different strains utilizing indigenous resources and scale up procedures Formulations for storage and transport Improvement of strain capability vis a vis pathogenicity, compatibility, desiccation tolerance Strong Founder populations with founder effects conserved as genetic deterioration or drift is likely to dilute these effects. * Dr. Adholeya is the Director, Division of Biotechnology & Management of Bioresources, TERI, New Delhi, and Dr. Sharma is a Fellow here. Dr. Hussaini is Principal Scientist (Nematology), Project Directorate on Biological Control (ICAR), HA Farm Post, Bellary Road, Bangalore 5