Efficiency of Local Isolates of Entomopathogenic Nematodes Steinernema spp. and Heterorhabditis spp. in Mortality of Potato Tuber Moth (Phthorimaea operculella) Larvae

Abstract

The potato tuber moth (PTM) Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is the most damaging potato pest in the world and is difficult to control as the larvae are internal feeders in the plant and tubers. This study aimed to develop an eco-friendly control method for the management of this pest. Accordingly, susceptibility of PTM to eight native isolates of entomopathogenic nematodes (EPNs) was tested using three concentrations 50, 100 and 200 infective juveniles (IJs)/ml at three temperatures (20, 25 and 30°C) under laboratory conditions. The results obtained showed the sensitivity of PTM for the eight isolates at the three temperatures, with different mortality rates. EPN isolates at all concentrations and at the three temperature levels achieved an average mortality rate higher than 50%. This indicates that the fourth instar of potato tuber moth larvae was highly affected by the local isolates. The average mortality rate of potato tuber moth larvae ranged between 63% at 30°C at the concentration of 50 IJ/ml to 100% at temperatures 20, 25 and 30°C and the concentration of 200 IJ/ml. The interaction between isolates and concentrations was significant at all temperature levels. It was shown that that the optimum temperature for most isolates was 25°C, where the average mortality rate reached 97.80, 96.70, 96.70, 95.60, 93.00 and 91.00 for the isolates of genus Steinernema RMD, RMF, RMN, RMJ, RMM and RMZ, respectively, at 25°C, whereas the isolates RMA and RMG belonging to the genus Heterorhabditis were sensitive at a temperature of 20°C, where the average mortality rate reached 86.70% and 83.30%, respectively, and at 30°C the mortality rate reached 100%. It can be concluded that the isolates belonging to the genus Steinernema preferred cold and moderate temperatures, whereas isolates belonging to the genus Heterorhabditis preferred high temperatures.

Keywords:

Potato tuber moth, entomopathogenic nematodes, temperature, average mortality rate.