BOTANICAL PESTICIDES: AN UPCOMING TOOL FOR PLANT PROTECTION

Meena Khetrapal 1 and Lata Vodwal 2 . 1. Department of Chemistry, Daulat Ram College, University of Delhi, Delhi, India. 2. Department of Chemistry, Maitreyi College, University of Delhi, Delhi, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

1779 the natural products (secondary metabolites) are found to be an excellent alternative to conventional synthetic pesticides as in this way, one can reduce the negative impact of pesticides on human health and on the environment. So, a move toward the approach of green chemistry and the continuing need for developing new crop protection tools with novel modes of action makes discovery and commercialization of natural products as "green pesticides" an attractive and profitable pursuit that is commanding attention. The concept of "green pesticides" refers to all types of nature-oriented components that are used to control the population of pests and ultimately increase the food production. These green pesticides are "safe or eco-friendly" and are also found to be more compatible with the environmental components than the synthetic pesticides 4 .
Introducing Botanical Pesticides as Green Pesticides:-All plants produce secondary metabolites that are phytotoxic to some degree and most of them are used as botanical pesticides. Extensive studies have been carried out on the use of these plant products both in the crude as well as commercial formulations against several pests without affecting their any natural enemies 5 . A large number of bioactive phytochemicals (Table 1) isolated from diverse sources are now known which have not only provided leads to the discovery of new pesticidal molecules, but have also helped in proper understanding of their mode of action. Commercial products based on Azadirachta Indica (neem) are known to affect more than 400 species of insects, mites, nematodes and fungi. Other traditionally insecticidal plants like Media, Chrysanthemum, Derris, Nicotiana, Tephrosia, Ryania, Sabadilla Annona, etc., have also earned world wide attention 6 . Armyworms, stink bugs, hariequin bugs, leafhoppers, cucumber beetles, blister beetles, cabbage loopers, etc. Several other plants like piper, capsicum, ginger, turmeric, etc. better known for their edible properties also exhibited a wide range of pest control properties including fecundity, phagodeterrent oviposion deterrent and growth disrupting effects.
The botanical pesticides are processed into various forms which include:- Preparation of crude plant material;  Plant extracts or resins; and  Pure chemical isolated from plants.

Botanical Insecticides-First to Fourth Generation Insecticide:-
The "first generation" insecticides referred as "botanicals", include plant extracts and plant secondary metabolites, such as nicotine, pyrethrum, rotenone, derris, quassin and sabadilla. Some of these botanical compounds form the foundation for the synthetic "second generation" pesticides. For example, pyrethrum isolated from Chrysanthemum flowers has become the basic unit for the synthetic pyrethroids and physostigmine from Physostigma venenosa has lead to the structurally similar synthetic carbamates. These "second generation" pesticides mostly are nerve poisons and affect not only the target pest but also the non target pest. But, there is no question that industries have helped to control he pest, in part time but the extreme and with this same reason in last two decades people moved away from the "second generation" synthetic pesticides. "Third generation" pesticides focused on insect growth regulators such as precocenes and phytoecdysones. The third generation pesticides are assumed to be more selective and environmentally safe; they usually work slowly and are not able to prevent insects from destroying a bulk amount of crop before dying. The "fourth generation" or "next" of pesticides depend upon the behavior modifying compounds like antifeedant and deterrents.

Botanical Pesticides as Olfactory Chemicals:-
Olfactory chemicals (Table 2) are usually essential oils with relatively high vapor pressure and are used to control the insect population at olfactory level. On the basis of movement and orientation towards or away from the source, they are designated as attractant or repellents or antifeedants. Specific Compounds with Significant Biological Activity:-Flowers, leaves or roots may be directly used as botanical pesticides (Table 3) in their powdered form or the bioactive compound may be extracted from the plants and utilized alone or in a mixtures with other toxicants and auxiliary materials to control the pest population. Plant gums are used as adhesives, saponins have spreading and emulsifying properties and essential oils are frequently attractive or repellent to insects. Soluble in water and organic solvents. Activity: Insecticide (botanical insecticide) Structure: c. Anabasine:- Source: it is a liquid alkaloid obtained from Nicotiana glauca (Family: Solanaceae).  Mode of action: nerve toxin  Use against: Aphis fabae, codling moth larvae, guinea pigs and rabbits etc.  Chemistry: IUPAC NAME: (S)-3-(2-piperidyl) pyridine Formula: C 10 H 14 N 2 Sp.gr.: 1.0481 g/cm 3 Boling point: 280-282 0 C. Solubility: Soluble in water and organic solvents Activity: Insecticide (botanical insecticide) Structure: d. Azadirachtin:- Source: it belongs to limonoids group and isolated from Neem tree. (Azadirachta indica; Family: Meliaceae).  Mode of action: repellent, antifeedant and reproduction inhibition.  Use against: insects belonging to order Coleopteran, Diptera, Heteroptera, omoptera, Hymenoptera, Lepidoptera and Orthoptera. e. Pyrethrum and Pyrethrins:- Source: it is an organic compounds isolated from dried flower head of the (Chrysanthemum cinerariaefolium; Family: Asteraceae). Pyrethrins (Table 4) are gradually substituting the demand of organophosphates and organohloride pesticides.  Mode of action: interferes with the Na + and K + exchange process in insect nerve fibers and also disturbs the normal transmission of their nerve impulses.  Use against: aphids, beetles, mealy bugs. leafhoppers, thrips, cabbage worms, loppers and many others.  Chemistry: the pyrethrins are naturally occurring esters formed as a result of combination of two acids: pyrethric acid and chrysanthemic acid with three alcohols. The pyrethrins are known for its knockdown and toxicity properties.
i. Ryanoidine:- Source: it is an alkaloid and isolated from woody stems of Ryania speciosa (Family; Salicaceae).  Mode of action: it causes muscular contractions and paralysis.  Use against: codling moths, japanese beetles, potato aphids, squash bugs, corn earworms, onion thrips and silkworms.

Conclusions:-
Heavy dependency on commercially available synthetic pesticides in the field of agriculture, over the years, has had a bad impact on environment and has lead to several problems like the increased tendency to developed the resistance in pests, increased insect outbreaks, suppression of predation and parasitoids and contamination of the food chain. But later on, because of the environmental hazards of random use of pesticides, the new generation of pesticides have emerged in the field i.e. "Botanicals" and "Green pesticides".