Morphological variations in the African palm weevil, Rhynchophorus phoenicis (F) (Coleoptera: Curculionidae), in Kenya and Uganda

Abstract

We investigated morphological differences in the African palm weevil (Rhynchophorus phoenicis) from Kenya (Busia and Kwale) and Uganda using a LEICA EZ4HD stereo microscope and an absolute digimatic caliper. Ten pronotal colour patterns were recorded, of which two (brown with two black spots and black with/without very faint brown bands of variable lengths and positions) are reported for the first time. Pronota of most R. phoenicis from Busia and Uganda were black with/without very faint brown bands of variable lengths and positions. Samples of R. phoenicis from Kwale were dominated by four reddish brown and three black bands, which either ran through the pronotal length or the reddish-brown bands coalesced anteriorly. The following pronotal colour patterns were male-specific: (i) two reddish brown bands, approximately ¾ the pronotal length and coalescing anteriorly, (ii) two reddish brown bands running through the pronotal length but discontinuous towards the posterior end and (iii) a brown pronotum with two black spots. Only the females had (i) two faint reddish brown bands running through the pronotal length, fading posteriorly and (ii) four reddish brown and three black bands, two of the former on either halves coalescing posteriorly. Females had longer snouts and mesocoxal distance, and wider elytra than males. Males possessed a longer profemur than females. Morphometric polymorphism was not linked to the site of sample collection. These findings provide additional diagnostic features and improve sexing of P. phoenicis and open opportunities for further research on the mechanisms for polymorphism in the species.