Survivability, growth performance and nutrient composition of the African Palm Weevil (Rhyncophorus phoenicis Fabricius) reared on Four different substrates

Abstract

Survivability, growth performance and nutrient composition of the African Palm weevil (APW) (Rhyncophorus phoenicis) reared on four different substrates was investigated following earlier finding that Sugar cane tops (SCT) and Spoilt water melon (SWM) could be useful in captive rearing of the weevil.  This necessitated a search into other waste fruits that could be used as media for rearing of APW as their infestation of oil and raffia palm is not only unfriendly to the environment but also wastage of economic resources. The growth and nutrient composition of the larvae in three waste fruits (Not rotten but not fit for human consumption): Spoilt Water Melon (SWM), Ripe Paw paw (RPP), Spoilt Pine apple (SPA) and Sugarcane tops (SCT:  Off Cut from the tip of sugarcane) were compared in this study. One hundred and twenty newly emerged APW larvae of similar weights collected from “Mgbo swamp” in Ebenebe town, Anambra State, Nigeria, were used for the study which lasted for ten weeks.  Thirty larvae were randomly assigned to each of the treatments (Culture media). The experiment was designed on a 4 x 3 Completely Randomized Designed, whereby each treatment had 30 APW larvae in three replicates of 10 larvae per replicate. The larvae were housed in plastic bowls of 30cm diameter and 40cm height. The bottom part of each bowl was perforated to let out moisture and the top covered with mosquito net to avoid flies. The substrates in each housing unit were removed and replaced with fresh ones on weekly basis to minimize microbial attack.  Survivability, growth performance in terms of weight gain and increase in linear body measurements within 10 weeks were monitored and used as indices of the suitability of each of the culture media. At the end of the experiment three larvae were randomly selected from each replicate and taken to the Biochemistry Department Laboratory, Nnamdi Azikiwe University, Awka for proximate analysis. The result of statistical analysis showed that percent survivability was highest in Sugar cane top (96.7%) and least in larva reared on Ripe Paw paws (66.7%).  The body weight and linear body measurement followed the same trend with those on SCT and SWM having the highest body weight increase of 4.13 + 0.11 g and 4.11 + 0.31 g respectively, while the ones on RPP had the least body weight increase of 2.7 + 0.06 g.  For the body length increase, the larva reared on SCT recorded 2.0 + 1.3 cm, those on SWM recorded 1.8 + 0.23 cm and the ones on RPP had the least body length increase of 0.9 + 0.1 cm. However, the crude protein percent of the larvae reared on SPA was highest (25.90%), followed by those on SCT (22.50%) and those on RPP recorded the least crude protein content of 21.25%. It is therefore recommended that Discarded/Spoilt water melon, Sugar cane tops and discarded ripe pineapple be used in the rearing of the larvae up to 10 weeks or before pupation.