Effect of Temperatures on the Pathogenicity of Entomopathogenic Nematodes (Steinernema carpocapsae and Heterorhabditis bacteriophora) for Biocontrol of Octodonta nipae (Maulik)

In the 21st century climate change has been recognized globally as the most impending, and critical issue that affects all animals including insects. In particular, temperature plays an important role in the development, reproduction, host searching, survival, pathogenicity, sex ratio and insect death. The Nipa palm hispid, Octodonta nipae (Maulik) is an important invasive pest of palm trees in Sothern China. Knowledge of how this beetle can be controlled with entomopathogenic nematodes under different environmental temperature is scarce. Therefore, the aims of this study were to test the efficacy of two entomopathogenic nematodes (Steinernema carpocapsae and Heterorhabditis bacteriophora) at different development temperatures. The pathogenicity was tested at concentration of 100 IJs larva-1 and treatment are kept at four temperatures of 20, 25, 30 and 36°C, 80 ± 5% RH. The results showed that, both nematodes species caused larval mortalities at all the tested temperatures except at 36°C. The highest larval mortalities of 85.3% and 40.6% were obtained at 30°C for both S. carpocapsae and H. bacteriophora respectively. Furthermore, both nematodes penetrated O. nipae larvae at all temperature conditions except at 36°C. Similarly, the highest penetrations of nematodes infective juveniles were recorded at 30°C for S. carpocapsae and H. bacteriophora. The study demonstrated that, warmer temperature enhanced the pathogenicity of nematodes, which in turns trade well with the unprecedented increase in environmental temperature under climate change, for integrated management of this beetle.