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

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\ub0C) for 5 days. Germination rates of these conidia before and after their exposure to heat were compared at 25 \ub0C 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 aw levels and the rate of germination of modified conidia of each isolate was significantly higher at 0.98 aw (F2, 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.La mouche blanche ( Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) est une redoubtable peste pour une large gamme de plantes cultiv\ue9es et ornementales d\u2019importance \ue9conomique dans Presque toutes les zones agro-\ue9cologiques du monde. L\u2019objectif de l\u2019\ue9tude \ue9tait d\u2019\ue9valuer l\u2019efficacit\ue9 des conidies d\u2019entomopathog\ue8nes Beauveria bassiana (BB 315), Isaria farinosa (ARSEF 5081) et Metarhizium anisopliae (Ma 275.86DC), contre la mouche blanche (Bemisia tabaci) sous climat tropical. Deux formes de chacun des trois isolats de conidie : (a) conidie modifi\ue9e (conidie ayant une potentialit\ue9 \ue9cologique am\ue9lior\ue9e), et (b) conidie non modifi\ue9e, ont \ue9t\ue9 soumis \ue0 une temp\ue9rature de 45\ub0C pendant 5 jours. Le taux de germination de ces conidies, avant et apr\ue8s leur exposition \ue0 la chaleur, a \ue9t\ue9 compar\ue9 \ue0 25 \ub0C sur un milieu de culture contenant du Sabouraud Dextrose Agar (SDA, aw= 0.995) afin d\u2019\ue9valuer leur r\ue9silience face \ue0 la tension thermique. Ensuite, le potentiel de germination des conidies a \ue9t\ue9 \ue9valu\ue9 \ue0 trois diff\ue9rents niveaux de disponibilit\ue9 en eau aw (0.995, 0.98 et 0.96). Enfin, les conidies ont \ue9t\ue9 test\ue9es contre l\u2019infestation des plants de tomate par B. tabaci, et les densit\ue9s d\u2019insectes apr\ue8s les traitements ont \ue9t\ue9 compar\ue9es avec l\u2019effet du faible taux de chlorpyriphos. Les taux de germination des conidies sur SDA variaient selon le niveau de disponibilit\ue9 en eau, en plus le taux de germination des conidies modifi\ue9es \ue9tait plus \ue9lev\ue9 chez avec les isolats \ue0 aw = 0.98 (F2, 16 =0.31, P=0.001). Les conidies modifi\ue9es de B. bassiana se sont r\ue9v\ue9l\ue9es les plus tol\ue9rantes \ue0 la tension thermique. A l\u2019oppos\ue9, les conidies de I. farinosa ou de M. anisopliae ont montr\ue9 des taux comparables de germination aux trois niveaux de aw . On note une r\ue9duction significative de l\u2019incidence de la peste apr\ue8s 14 jours, en ref\ue9rence au control. De plus, il n\u2019y a pas de diff\ue9rence significative (P>0.05) entre l\u2019\ue9tat modifi\ue9 et non modifi\ue9 des conidies en rapport avec leur r\ue9action contre B. tabaci