Rearing tomato whitefly and field evaluation of modified and unmodified conidia of Beauveria bassiana, Isaria farinosa, Metarhizium anisopliae and low rates of Chlorpyrifos under tropical conditions

Abstract

The whitefly (Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a serious pest of a wide range of economically important agricultural and ornamental crops in all agro-ecological regions in the world. This study evaluated the efficacy of conidia of entomopathogenic Beauveria bassiana (BB 315), Isaria farinosa (ARSEF 5081) and Metarhizium anisopliae (Ma 275.86DC), against whitefly (Bemisia tabaci) under tropical climate. Two forms of conidia: (a) modified conidia (conidia with improved ecological competence), and (b) unmodified conidia of the three isolates were subjected to heat treatment (45°C) for 5 days. Germination rates of these conidia before and after their exposure to heat were compared at 25 °C on Sabouraud Dextrose Agar (SDA, aw= 0.995) to assess resilience to heat stress. Further, assessment of germination potentials of conidia was conducted at three aw levels (0.995, 0.98 and 0.96: corresponding to different levels of water availability). Thereafter, they were tested against B. tabaci infestation on tomato plants and insect densities after the treatments were compared with the effect of low rate chlorpyrifos. The conidia germinated differently on SDA at the three a_w levels and the rate of germination of modified conidia of each isolate was significantly higher at 0.98 a_w (F_{2, 16} =0.31, P=0.001). Modified conidia of B. bassiana appeared more tolerant to temperature stress. All the isolates significantly reduced pest incidencerelative to control after 14 days and there was no significant difference (P>0.05) between the effect of modified and unmodified conidia against B. tabaci in the field. The level of control achieved using the conidia of the three fungal isolates was comparable with the chlorpyrifos treatment.

Key Words: Bemisia tabaci, entomopathogen, water activity