Bioefficacy of Extracts of Hyptis suaveolens, Eugenia aromatica and Azadirachta indica as Field Protectants of Pawpaw Against Paracoccus marginatus Will. and Granara de Willink in Ibadan, Southwest Nigeria

Abstract

The papaya mealybug, Paracoccus marginatus is a small sized polyphagous invasive hemipteran bug that attacks several genera of host plants, causing considerable yield loss. Commonly used insecticidal control is being discouraged due to environmental and human health hazards. Information on the control of this pest with botanicals is scanty, therefore the control using selected botanicals was investigated. Aqueous and ethanolic extracts of three botanicals: Hyptis suaveolens, Eugenia aromatica and Azadirachta indica were evaluated in screen cages (1.80×0.60×1.50m) for contact toxicity following standard procedures. Cypermethrin® (100 ml a.i ha-1) was used as a standard check. The secondary metabolites in the three plants were analyzed for saponins, alkaloids, terpenoids, phenols, flavonoids and cardinolides following standard procedures. Effective concentration was determined using probit analysis. Both aqueous and ethanolic extracts of the botanicals caused adult mortality of P. marginatus. However, the difference in percentage mortality in aqueous extracts of A. indica (54.28±1.7), H. suaveolens (47.5±4.1) and E. aromatica (48.6±1.1) were not significant (P>0.05). Percentage mortality of ethanolic extracts of A. indica (87.40±4.8) was significantly higher (P<0.05) than both E. aromatica (74.40.16±2.4) and H. suaveolens (72.10.58±2.8). Concentration of the secondary metabolites varied in the botanicals with H. suaveolens having higher flavonoids (107.08mg/100g), cardinolides (46.06 mg/100g) and terpenoids (3.17mg/100g) while A. indica had higher saponins (10.33mg/100g) and phenols (1938.48mg/100g) while E. aromatica had comparatively higher alkaloids (0.59%). The LC50 ranged from 3.61mg/kg in A. indica, to 4.64mg/kg in E. aromatica and 4.52mg/kg in H. suaveolens. The ethanolic extracts of botanicals evaluated were more effective than the aqueous extracts and can serve as a substitute to the synthetic insecticides for the control of P. marginatus.