Studies on the efficacy of neem seed extracts and the mixture of neem seed, galanga and lemon grass in controlling the American bollworm (Heliothis armigera Hubner)

Effectiveness of plant extracts namely neem seed (Azadirachta indica var. simensis), galanga rhizome (Alpinia galanga) and lemon grass leaves (Cymbopogon citratus) to American bollworm (Heliothis armigera Hubner) as stomach-, contact poison, egg laying and oviposition deterrent were studied in the laboratory and in the field. Results from laboratory had shown that alcohol neem seed extract at 5 percent has the highest stomach poison causing larval mortality at 86 percent followed by lemon grass and galanga at 36 percent and 32 percent respectively. The mixture of neem seed, lemon grass and galanga extracts were not effective as contact poison but, when the 0.2 percent piperonyl butoxide or 0.6 percent white oil were added into neem seed extract at 5 percent then the larval mortality will be increased from 3 percent to 30 percent. No effect on egg laying of the adult female after sprayed the plant extracts as contact poison to the second instar larvae. However, these extracts were fed to the fourth instar larvae as stomach poison there the egg laying will be decreased about 50 percent. The neem seed and the lemon grass extracts deterred the oviposition of the adult female at 50 percent but none from galanga extract. Result from the field experimentation revealed that when the extracted substances from plants and alphamethrin were sprayed onto cotton leaves as stomach poison, after 1 day and 3 days interval the cotton leaves were collected and fed to the second and fourth instar larvae. Within 1 day, the neem seed extract has shown the highest mortality range from 73-83 percent but had no significant from alphamethrin to the second instar larvae. Within 3 days the second instar larval mortality was rapidly decreased except Nlm 5 percent and alcohol extract 5 percent were 70 percent and 47 percent, when compared to the mortality of alphamethrin at 27 percent. The fourth instar larval mortality was relatively low after these substances were sprayed for 1 day. The percent mortality was about 28-35 percent which has no significant to alphamethrin.