Population Dynamics of African Palm Weevil (Rhynchophorus phoenicis F.) on Breeding Sites of Oil Palm (Elaeis guineensis Jacq.) in Niger Delta, Nigeria

Abstract

Population dynamics of African palm weevil (APW) (Rhynchophorus phoenicis F.) was studied. Four oil palms were randomly selected and sizeable wounds were created, using an axe and cutlass and monitored for arrival of APWs for 21 days. Total number of one hundred and fourty-eighty (n=148) weevils were counted at the breeding sites. The total number of males was 52(35.13%), while the total number of females was 96(64.87%) which corresponds to sex-ratio of 1:1.9. Colonization of the breeding sites commenced with the arrival of few females in the morning (7-9am) followed by the males at noon (1-2pm) and significantly increased in population to peak by 1-3pm till evening and steadily declined at dusk. The population of APWs was significantly higher (P<0.05) in younger oil palms than older palms: Youngest Palm (P1) had 62, Younger Palm (P2) had 66 and Older Palm (P3) had only 20, while the Oldest matured Palm (P4) had no weevil because the tissues did not decompose. Optimum temperature and relative humidity which favoured the aggregation of R. phoenicis at the breeding site was 300C - 310C and 75-82% respectively. Also, the population of R. phoenicis at the breeding sites was highly positively and negatively correlated with the temperature (r=0.96) and relative humidity (r=-0.98) respectively. The APWs were sluggish in the morning but became active in feeding, courtship, mating and oviposition of eggs at noon when the temperature of the day become hotter and declined at dusk.