The Potential of Native Palestinian Nomuraea rileyi Isolates in the Biocontrol of Corn Earworm Helicoverpa (Heliothis) armigera

Izz- aldien I. Iqtiat, Mohammad I. Al-Masri, Radwan M. Barakat


Four native isolates of the entomopathogenic fungus Nomuraea rileyi were isolated from soil samples collected from 210 different irrigated and non-irrigated tomato-growing fields in the West Bank- Palestine. The four isolates were recovered from soil samples collected from the Jenin area during August 2006 (Nr 3, Nr 5, Nr 17 and Nr 18), and were then deposited at the US Agriculture Research Service collection of Entomopathogenic Fungi (ARSEF 7794, ARSEF7793, ARSEF7792 and ARSEF 7791). The isolation was carried out by using dilute plate technique on modified selective medium. The medium used in the study was based on the standard Saboraud's maltose agar yeast extract, and modified by adding Tween® 80 and the fungicide dodine® (SMAYTD).

The effect of temperature on sporulation, spore germination and mycelial growth of the entomopathogenic fungus, N. rileyi, were studied in vitro. The fungus favored relatively moderate temperature (15-25oC) for germination, sporulation and mycelial growth. The growth of isolates was completely inhibited at 35oC. The virulence of N. rileyi native isolates against Helicoverpa armigera was investigated in terms of lethal time (LT50) and lethal concentration (LC50). The results showed that the LT50 for these isolates at the inoculum concentration of 108 spore ml-1 were in the range of 7.9 to 9.4 days. The LC50 was in the range of 105 and 106 spore ml-1. The virulence of the most promising isolate (ARSEF 7794) compared to the insecticide Thyonex® was evaluated on H. armigera under tomato open field conditions; the results showed that the fungus and the insecticide reduced tomato infestation by 46%, and 88% respectively, compared to the control.

الكلمات المفتاحية

Helicoverpa armigera, Nomuraea rileyi, Biological Control, Virulence, Entomopathogenic Fungi.

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