Efficacy of two species of entomopathogenic fungi against the stored-grain pest, Sitophilus granarius L. (Curculionidae: Coleoptera), via oral ingestion

Sitophilus granarius is a serious stored-grain insect that can destroy the whole grain of cereal crops. The present research demonstrated that two species of entomopathogenic fungi (EPF), Beauveria bassiana and Metarhizium anisoplidae , killed the treated adults of S. granarius when applied via oral ingestion. Mortality of S. granarius was shown by growth and development of the ingested conidia in the insect gut causing death of infected insects. During bioassays, the fungus conidia were mixed with wheat flour then provided to the insects for feeding on the mixture for 24 h. The insects were surface-treated with a contact fungicide (Merpan ® ) to kill the external conidia that could penetrate the cuticle and develop to kill the infected insects. Results indicated that the most effective ratio of mixing fungus conidia with the wheat flour was 0.1:2.0 (g/g) where this ratio should contain 2.75 × 10 8 conidia/g of M. anisopliae mixture or 2.6 × 10 8 conidia/g of B. bassiana mixture. Ingested conidia of each fungus caused a first mortality of S. granarius adults after 10 and 12 days of B. bassiana and M. anisopliae treatments, respectively. They also caused 50% mortality after 2.787 and 3.047 weeks of treatments for the same fungi, respectively. The novelty of this research is in adjusting and applying a technique of disinfection of insect cuticle with a fungicide and then verifying the presence of applied fungi in the infected insects. The practical application of this method was discussed.