Lethal and sub-lethal effects of Cordyceps fumosorosea on the demography and biochemistry of Phenacoccus solenopsis

The cotton mealybug, Phenacoccus solenopsis Tinsley, is a highly invasive pest of cotton. The use of entomopathogenic fungi as a bio-pesticide could provide an alternative to current chemical control measures that preserve the environment and biodiversity, and ensures good quality of crops. Lethal, sub-lethal and trans-generational studies are needed to assess the effects of myco-insecticides on such pests. The pathogenicity of different spore concentrations of Cordyceps fumosorosea Wize was assessed against second-instar nymphs by immersion while focusing on lethal (LC50) and sub-lethal (LC30) spore concentration treatments of C. fumosorosea on filial (F-0) and first filial (F-1) generations. After treatment at LC50 and LC30 spore concentrations of C. fumosorosea, the progeny of P. solenopsis showed reduced nymphal duration, adult longevity and fecundity as compared with controls. Also, total pre-oviposition period (TPOP), adult pre-oviposition period (APOP) and oviposition days (O-d) were reduced with the increasing spore concentration of C. fumosorosea. In addition, population growth parameters such as net reproductive rates (Ro) and mean generation time (T) were dramatically reduced. The level of expression of acetylcholinesterase (AChE), esterases (EST), acid and alkaline phosphatases (ACP, ALP) and glutathione S-transferases (GST) were also examined. Significant expression of EST, GST, ALP, ACP and AChE (7.15, 4.51, 4.54, 2.80 and 8.32 mu mol/min of mg/ml protein), respectively were observed at 8 x 10(7) conidia/mL of C. fumosorosea. Pathogenicity even at sub-lethal doses as well as the production of detoxifying enzymes indicates that C. fumosorosea is the most effective fungus against P. solenopsis.