Abstract
In the present research, the toxicity, antifeedant activity and biological effects of ethanolic leaves extract of four medicinal plants named Eucalyptus rostrata, Dodonea viscosa, Rhyza stricta and Cymbopogon schoenanthus were evaluated on 2nd, 3rd and 4th instar larvae of H. armigera under laboratory condition. The results showed that values of LC50 in mg of different plant extracts in mg/100ml of the larval diet can be arranged in an ascending order as follows: Dodonea 7.23 > Cymbopogon 12.59 > Rhazya 14.52 > Eucalyptus 29.42 mg/100ml diet (the least LC50 is more toxic than the higher one). All the tested extracts had antifeedant and starvation effects against the 2nd, 3rd, 4th instar larvae. D. viscose extract possesses the least antifeedant effect even of their higher toxicity. There was clear relation between the percent of starvation and antifeedant of the 2nd, 3rd and 4th larval instar. All extracts were nearly the same in their effect on the biotic potential; of the insect, and possess latent effect when tested against 2nd instar larvae, the value of LC 50 of the extract was added to the diet, extracts increased larval duration, deformation between pupae and adult stages, moths sterility, increased as decreasing in females egg production. Other effects were noticed, reduction in percentage of pupation and moths emergence. The plant extracts can be arranged ascending according to percentage of their sterility effects as follows: C. schoenanthus < E. rostrata < R. stricta < D. viscose. All extracts cause disruption on the biology and physiology of the insect, and all extract induced percentages of deformation between pupal and moth stages. The ethanolic extract of the plant leaves of the tested plans may be used for control H. armigera in combination with other methods in the integrated program in order to decrease the buildup of the resistance and protect the environment from chemical pollution.
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