ESSENTIAL OILS - A POTENT SOURCE OF NATURAL PESTICIDES

A wide variety of essential oils and their constituents possess varyin g degrees of pest controlling properties. The plant extracts/essential oils of Mentha piperita, Acorus calamus, Anethum sowa, Piper nigrum, Pongamia glabra and Azadirachta indica have been shown to exhibit grai n protectants activity. It is pointed out that the alcoholic and pheno lic constituents of essential oils show considerable toxicity to contr ol egg hatching of Aedes aegypti. The oil of Acorus calamus inhibit em bryonic development of Dysdercus koenigii at 100 ppm concentration. It is described that the volatile oils of Eucalyptus, Japanese mint, dil l, turpentine and citronella show different degrees of attractant and repellent activity against rice weevil (Sitophilus oryzae), pulse beet le (Calloso bruchus chinensis), spice beetle (Stegobium paniceum) and house fly (Musca domestica). The volatile constituents of several esse ntial oils mainly mono- and sesquiterpenoids have been shown to exhibi t strong repellent activity against house fly and cockroaches. It is d ocumented that the volatile oils containing aliphatic straight chain k etones and aryl ketonic compounds also exhibit strong repelling tenden cy against bees. The mono-, sesqui-, di- and triterpenoids isolated fr om several aromatic plant species have been shown to possess potential antifeedant activity by contact action. It is described that the nero l, geraniol and citronellol act as Juvenile hormone (JH) analogues. Th e volatile oil of Lantana camara also exhibit JH like activity on fres h 5th instar nymphs of Dysdercus similies. It is argued that the major ity of essential oils and their constituents are potent antifungal and antibacterial agents. Some of the oils such as Citrus sinensis and Hy ptis suaveolens are found to be more potent than commercial synthetic fungicides, and exhibit no phytotoxic effect on seedling growth and se ed germination of green gram ( Vigna radiata). It is described that na turally occurring essential oils and their constituents also exhibit r emarkable toxicity against some parasitic worms.