ASSESSMENT OF THE ENTOMOPATHOGENIC FUNGUS BEAUVERIA BASSIANA SAUDI ARABIAN ISOLATE (B - SA3) AGAINST THE DEVELOPMENTAL STAGES OF THE RED PALM WEEVIL, RHYNOCHOPHORUS FERRUNGINEUS (OLIV.)

The efficacy of the entomopathogenic fungus Beaveria bassiana Saudi Arabian isolate (B-SA3)was evaluated against the red palm weevil, Rynochophorus ferrungineus (Oliv.).The mentioned isolate was assessed on the different developmental stages of the red palm weevil through toxicity tests, i.e. determination of lethal concentration and lethal times to kill 50% of treated insects. The results showed that 8th instar larvae were the most tolerant followed by pupa to B.bassiana as their LC50 values were 3.75x 108 and 3.78x 107 conidia/ ml, respectively. Meanwhile, 4th instar larvae were the most susceptible to infection by B.bassiana (B-SA 3), as LC50 value was 3.25x 106 conidia/ ml, which proved insignificantly different to that determined in adult weevils, i.e. 4.18x 106 conidia /ml. Furthermore, LT50 values were very similar in these latter mentioned developmental stages in any considered concentration; meanwhile, LT50 was much longer in 8th instar larvae than the other considered instar and/or developmental stages. The fungus B. bassiana was most virulent to eggs of the red palm weevil as none of the eggs hatched following their treatment with any of the considered concentrations (ranging between 5x 109 to 5x105 conidia /ml). Moreover, germination viability of harvested conidia of B.bassiana stored at -4°C was insignificantly affected up to the 10th month storage period and was well above 90%. However, germination percentage of conidia then decreased to 70.27% after 16 months of storage. Also, the virulence of the stored conidia was tested after 1, 6, 12 and 16 months on adult red palm weevils, the LC50 values were 3.75x106, 4.66x106, 4.17x107 and 3.37x108 conidia/ ml, respectively. These results show that there was a significant decrease in the virulence of the tested fungus when the duration of storage period was more than 10 months.