Morphometric analysis of larval instar stages of reared Red Palm Weevil, Rhynchophorus Ferrugineus (Oliver, 1790), (Coleoptera:Curcolionidae)

Abstract

This study was conducted to explore alternative morphometric characters that could be used to estimate the larval age of red palm weevil (RPW), Rhynchophorus ferrugineus. A total of 14 characters explored in the study. Morphological characters were measured using Image J software and data were analyzed using One-way analysis of variance (ANOVA), principal components analysis (PCA), and discriminant function analysis (DFA). One-way ANOVA excluded characters that are not different among instars, which were distal head band (DB), basal head band (BB), distal tail width (DT), tail ratio (TR), and head band ratio (HBR). All other characters were found to be significant at p < 0.05. For PCA, cumulative variations of 88.7% from the first two principal components, evidenced by sharp decrease in slope of the scree plot, has resulted from high loadings in dorsal surface area (DSA), total surface area (TSA), ventral surface area (VSA), head capsule width (HW), body length (BL) ranging from 0.955 to 0.984. For DFA, only one function explained a canonical correlation of 0.986 with 94.9% variation, and Wilk’s Lambda statistics of (0.007). The highest character loadings were BL, DSA, and HW, and could be useful characters in distinguishing instar ages of RPW larvae.