Anti-feeding effects of sublethal concentrations of fungus Beauveria bassiana Balsamo, Beauveria brongniartii Saccardo and Metarhizium anisopliae Metsch on the date's horn beetle larvae Oryctes elegans Prell

The effects of sub-lethal doses of the fungi, B.bassiana, B.brongniartii and M. anisopliae on feeding ability of the larvae of the date horned beetle and the indices of digestion, absorption and excretion of this pest were studied in laboratory condition. First, the sub-lethal doses of 50 and 90% of reducing power ability (EC50 and EC90)was calculated and then the physiological feeding indices including Relative Consumption Rate) RCR), Efficiency of Conversion of Ingested food (ECI, Efficiency of Digested food (ECD), Approximate Digestibility (AD) were estimated. The results showed that the isolates of all three pathogenic fungi had a significant different high ability to reduce the feeding efficiency of the date- pest larvae. The highest and lowest abilities belonged to M. anisopliae and B. bassiana with the EC50 of 4.27×and 7.9 ×spores/ml, respectively. There was a significant difference between physiological feeding indices of the pest larvae when they were exposed to applied doses of spores. In all three pathogenic fungi species, increasing doses of spore decreased the values of MRG, ECI, ECD and AD, but increased the value of PCR. The highest of the regression lines of the indices on log scale of doses was recorded in M. anisopliae and then the two other species, B. brongniartii and B. bassiana.