LARVICIDAL AND GROWTH REGULATORY ACTIVITIES OF SOME ESSENTIAL OILS AGAINST ASIAN ARMY WORM, SPODOPTERA LITURA (FAB.)

Abstract

ABSTRACT Six medicinal plant essential oils viz., Foeniculum vulgare (saunf), Hedychium spicatum (kapoor kachri), Jatropha curcas (ratanjot), Piper nigrum (black pepper), Syzygium aromaticum (clove) and Vetiveria zizanioides (khas) were evaluated for their insecticidal and growth regulatory activities against third instar larvae of Asian army worm, Spodoptera litura. During preliminary screening, essential oils were tested at 1 and 2% concentrations. Highest mortality (100%) was found in saunf and khas oil, followed by clove oil (93.33%), ratanjot oil (73.33%) and black pepper oil (43.33%) and lowest in kapoor kachri oil (16.66%) at 2%.Lowest weight gain per larva 2DAF (days after feeding) was seen in clove oil (-0.025g and -0.06g) at 1 and 2% respectively and black pepper oil (- 0.06g) at 2%, while ratanjot, khas and kapoor kachri oil did not show any significant effects on weight gain parameter in comparison to control. Similar trend was observed in growth of the larvae, where clove and black pepper oils caused reduction in growth over control by -15.15 and -11.11% and 37.37 and 21.21% at 1 and 2% respectively. Based on this data, further five concentrations viz., 2.5, 2.0, 1.5, 1.0 and 0.5% were used to determine LC50 of ratanjot, clove and khas oil. Khas and clove oils were toxic at 6 and 12 HAE (hrs after exposure), the LC50 values being 1.95% and 0.85% at 6 hrs , 2.25% and 1.38% at 12 hrs respectively. Ratanjot oil was toxic at 12, 24, 36, 48 and 72 HAE with LC50 values of 1.37, 1.22, 1.15, 1.06 and 1.04%. A comparative dose mortality response expressed in terms of relative toxicity (RT) indicated that at 12 HAE, the RT values for ratanjot, clove and khas oils were 1.00, 1.00 and 1.86 respectively. The results demonstrate that essential oils of ratanjot, khas and clove may serve as a tool in the management of S. litura.