Bioactivity Of 58 Chinese Herbs Against Helicoverpa Armigera

In order to screen their insecticidal activities, 58 varieties of Chinese medicinal herbs were tested on the Helicoverpa armigera. Active substances were extracted with different solvents from one of them and its bioactivity upon the Helicoverpa armigera was determined. The main results are as follows:1. All the 58 varieties of Chinese herbs were preliminarily screened through diet incorporation method against the larvae of Helicoverpa armigera. After three days, 10 varieties of Chinese herbs showed inhibition rates of the larvae weight which was above 80%, and there were 21 varieties after five days. The weight inhibition rates of ZY-54, ZY-55, ZY-56, ZY-57 and ZY-58 were more than 95% after five days. 2.The ZY-56 was extracted with solvents of water, mineral ether and ethanol, water showed the largest extracting rates, next was ethanol, and mineral ether was the smallest one. The insecticidal activities of these three extracts were screened on the larvae of Helicoverpa armigera. The results indicated that the ethanol extract of ZY-56 had higher properties of antifeedant and contact toxicity to the larvae, which mainly manifested as significant growth inhibition. The mineral ether extract presented some antifeedant activity to the larvae, but had no contact toxicity and growth inhibition. The water extract had no insecticidal activity to the larvae.3.The ZY-56 was extracted with different concentrations of ethanol, and the bioactivity of extracts against the larvae of Helicoverpa armigerma were studied. The results showed the 85% ethanol extract had the highest bioactivity on the larvae, the 95% ethanol extract was the second, and the 55% ethanol extract was the least. The 85% ethanol extract had good antifeedant effects and contact toxicity to the larvae, the antifeedant rate after 48h was 38.4% and the rectified mortality after 72h was 51.7% respectively. The 85% ethanol extract had strong growth inhibition on the larvae, after treated with extracts, the average weight of larvae was only 34.6mg on the fifth day, but those of the contrast reached 417.2mg.The larvae couldn't recover to the normal growth instantly after treated with normal feedstuff, the pupation rate was 6.7%, the larvae instars delayed for 7 days. 4.The bioactivity of the 85% ethanol extracts were studied. Results showed that the extracts had higher contact toxicity and antifeedant properties on the larvae of Helicoverpa armigerma, the Median Antifeedant Concentration (AFC50) was 1.61mg/mL, the LC50 was 0.799 mg/mL. The extracts had significant growth inhibition on the larvae. With the augment of extracts concentration, the growth inhibition effect was stronger. Compared...