Larval instars determination for the twig borer weevil (Coleoptera: Curculionidae) of Falcataria moluccana (Miq.) Barneby & Grimes in Moluccas, Indonesia

Abstract

Abstract In establishing an integrated pest control strategy, it is important first to discover the life history of a potential agent, including the number of larval instars. The snout-weevil of the tribe Ithyporini Genus species (Coleoptera: Curculionidae) is a holometabolous insect that attacks Falcataria moluccana, a native tree of the Moluccas (Maluku), Indonesia. Preliminary observations show that their larvae feed and develop as a twig borer, making direct observation of their development complicated. This study aimed to determine the number of larval instars by measuring the head capsule width (HCW) and the growth pattern of larvae. As many as 940 larvae of all sizes were collected from three islands in Maluku Province: Ambon, Seram, and Haruku. Kernel density estimation (KDE) and Gaussian mixture model (GMM) were used for data analysis. The growth instars were verified using Brooks-Dyar’s rule. The results indicated four peaks in the frequency distribution from KDE, and cluster four showed the best-fit model from GMM. The growth ratio of HCW was 1.47, which also agrees with Brooks-Dyar’s rule that the growth ratio was consistent and followed a constant geometric. Thus, this research concluded that there were four instars for Ithyporini Gen. sp. larvae.