FUNCTIONAL AND NUMERICAL RESPONSES OF EXOCHOMUS FLAVIPES THUNBERG (COLEOPTERA: COCCINELLIDAE), A LOCAL PREDATOR OF THE CASSAVA MEALYBUG, PHENACOCCUS MANIHOTI MATILE- FERRORE (HOMOPTERA: PSEUDOCOCCIDAE)

Abstract

Laboratory studies were conducted to assess the functional and numerical responses of adult females of Exochomus flavipes, as a predator of Phenacoccus manihoti the cassava mealybug (CMB). Day old eggs of CMB at densities of 100, 200, 300, 400, 500, 600 and 700 were fed to young adult females of E. flavipes. Each density was replicated 6 times. Number of eggs consumed (Functional response) and number of eggs laid (Numerical response) daily were recorded. Generally, eggs consumption per day increased significantly with increase in prey density and a significant correlation (P<0.05) between mean number of CMB eggs consumed per predator and prey density (r=0.956) was observed. No significant (P>0.05) difference was observed in prey consumption between prey densities of 500 and 700. There was increased prey consumption from 44% at prey density 200 to 67% at prey density 400 per day, while percentage prey consumption decreased from 65.4% at prey density 500 to 48% at prey density of 700.  Number of eggs laid by adult E .flavipes increased with increase in prey density. The correlation coefficient between number of CMB eggs consumed and the number of eggs laid by E. flavipes was highly significant (r=0.9908) (P< 0.05).With increase in prey density,  the pre oviposition period reduced from 9 days at 100 prey density to 4 days at 700 prey density. Also, oviposition period and longevity of adult E.flavipes were observed to increase significantly (P<.05: r=0.9524) (P<0.05:0.9481) respectively, with increase in prey density. From the result of this study, it may be said that E. flavipes has potentials to be exploited as a biocontrol agent of mealybugs.