Toxicity and insect growth regulatory effects of root extract from the medicinal plant, Withania somnifera (Linnaeus) against red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae)

Abstract

The insect growth regulatory effects of the medicinal plant, Withania somnifera (Family: Solanaceae) on the moulting and metamorphosis of economically important stored grain pest, Tribolium castaneum (Coleoptera: Tenebrionidae) were assessed under laboratory conditions. Seventh instar larvae of the red flour beetle, T. castaneum were topically treated with different doses of root extract of W. somnifera. Treatment with root extract of W. somnifera disrupted growth, development, moulting and metamorphosis in T. castaneum. The results included mortality, prolongation of larval-pupal and pupal-adult ecdysis, ecdysial stasis, development of larval-pupal and pupal-adult intermediates and adultoids, eclosion inhibition, reduced pupation and adult emergence. The LC50 value in topical application of root extract of W. somnifera was 0.5850 µg·µL−1 against last instar larvae of T. castaneum. These results are similar to those observed by the application of juvenile hormone analogues and may be due to interference with the normal hormonal mechanism of moulting and metamorphosis.