Virulence of Steinernema carpocapsae and Heterorhabditis indica against coconut rhinoceros beetle, Oryctes rhinoceros L. (Scarabaeidae: Coleoptera).

Abstract

Biological control potential of two entomopathogenic nematodes, Heterorhabditis indica and Steinernema carpocapsae, was tested against neonate-, and third-instar grubs of Orycuts rhinoceros in laboratory and micro-plot experiments. The main aim of the study was to develop an efficient sustainable control method against the pest. With this we could develop a strategy of coconut production with the intention of diminishing or even preventing the appearance of pest resistance to insecticides. In the laboratory experiments, S. carpocapsae and H. indica were highly virulent to neonate grubs. Neonate grubs were susceptible to S. carpocapsae followed by H. indica. The virulence of the nematode species relative to each other differed greatly to neonate grubs but not to the 3rd instar grubs. In all the experiments, mortality of rhinoceros grubs varied significantly among nematode dose and days after treatment. In comparison of neonate grubs mortality, 3rd instar grubs require more number of nematodes. The dosage and time mortality relationship of S. carpocapsae and H. indica against the neonate and 3rd instar stage of O. rhinoceros indicated that as the dosage increased the susceptibility also increased. The susceptibility of the developmental stages of O. rhinoceros differed greatly among tested concentrations of nematode species and time. Our observations, combined with those of previous studies on other nematode and white grub species, show that nematode virulence against rhinoceros grub developmental stages varies with time and nematode concentration.