Mortality factors on the hibernating larvae of the corn borer Sesamia cretica Led. (Phalaenidae: Lepidoptera)


This study was conducted on the hibernating larvae of the corn borer, Sesamia cretica Led. after the harvest of sorghum crop at the experimental fields of the college of Agriculture in Abu-Ghraib, Baghdad of the fall season 2008. Laboratory results showed the isolation and identification of two entomopathogenic fungi, Metarhizium anisopliae (Metchnikoff) Sorokin, Verticillium lecanii, the bacteria Bacillus subtilis and the Ichneumonid wasp Coelichneumon sp. (Ichneumonidae: Hymenoptera) from the hibernating larvae of the corn borer S. cretica which considered to be as a new records on the corn borer in Iraq. Symptoms of the infection on hibernating larvae begans on January and continued till the emergence of the first generation of the borer. Laboratory inspection of 706 hibernating larvae showed mortalities of 7.22%, 0.70%, 0.99% and 0.42% for entomopathogenic fungi, bacteria, Ichneumon wasp Coelichneumon sp and for unknown reasons respectively, However fungal parasitism was considered to be the most important and could have a role as a mortality factor for the hibernating larvae that decrease adult emergence from the hibernation. Results of the pathogencity test of M. anisopliae on different stages of the borer revealed that fungus suspension caused significant and high mortality rates on eggs, reaches more than 98% after 3 days of treatment. Mortality of the fifth instars' larvae after 6 days was 23.3%. Percentage of treated larvae reached pupal stage was 63.3% compared with 90% for the control treatment. However pupal stage found to be less sensitive to pathogen infection, mortality rates found to be decreased to only about 6.6%. The possible use of the entomopathogenic fungi M. anisopliae after its formulation as a biocontrol agent for the corn stem borer and other insect pest was also discussed.