Virulence of Indigenous Isolates of Metarhizium anisopliae to Life Stages of the Coconut Rhinoceros Beetle (Coleoptera: Scarabaeidae: Dynastinae) in Papua New Guinea

Abstract

Coconut, Cocos nucifera L., is important crop in PNG and has been challenged with the invasion of pests. The coconut rhinoceros beetle (CRB), Oryctes rhinoceros is a serious pest to coconut and threatens the oil palm industry. In recent years, CRB-G biotype evaded the existing biological control agent Oryctes nudivirus introduced into the Pacific Islands, in the 1960s. Using pheromone trapping and visual rating, this study assessed population and damage by CRB in Markham Valley, Morobe province; and investigated the virulence of two indigenous isolates of Metarhizium anisopliae on CRB life stages by topical inoculation under laboratory conditions. Moderate damage levels was recorded on coconut palms in Daeng villages. Mixed sex CRB were caught in the 3 seasons of trapping, with more males trapped than females at the sites. Laboratory tests revealed that the two isolates varied in germination, time to sporulation on cadaver and virulence. Larval and adult CRB survival decreased by 20% through time when inoculated with the spores of M. anisopliae. At 21 and 25 DAI, isolate Ma2 caused high mortality at the shortest time on the larval (82%) and adult (80%), respectively. Isolate Ma2 has the potential as a microbial control agent against CRB.