Efficacy of Several Plant Extracts as Growth Inhibitors against Red Flour Beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Ethanol and acetone extracts of Verbena tenuisecta, Parthenium hysterophorus, Calotropis procera and Azadirachta indica were tested as inhibitors of the growth of Tribolium castaneum. V tenuisecta (at 500 ppm) effectively controlled eggs laying of T castaneum, i.e., the minimum mean number of eggs was 61.00, followed by the standard A. indica at 1000 ppm with 77.50 eggs, while the maximum mean oviposition amounted up to 139.67 and 144.67 eggs in flour treated with P hysterophorus at 500 and 250 ppm, respectively. The most effective plant extract as an inhibitor of egg hatching (applied as 500 ppm) was the extract of P. hysterophorus (only 18.47% of eggs hatched) while the least effective was the extract of V tenuisecta (52.03% of eggs hatched) 500 ppm each, respectively. The highest larval inhibition was exhibited by C. procera at 1000 ppm, which did not differ significantly from any of the other treatments or the control. Pupal inhibition was highest for the extract of V tenuisecta. The acetone extract had more effect on egg laying, while ethanol had the highest growth inhibiting effect as egg hatching inhibitor, larval inhibitor, pupal inhibitor and feeding deterrent. Growth inhibiting effects of plant extracts were not clearly dose-dependent. Ethanol extracts had better growth inhibiting effects than petroleum ether extracts, whereas acetone extracts had some effect on egg laying.