Larvicidal activity of endophytic fungal extract of Cochliobolus spicifer (Pleosporales: Pleosporaceae) on Aedes caspius and Culex pipiens (Diptera: Culicidae)

Endophytic microorganisms are fungi or bacteria which live inside plant tissues or organs, without causing them any harmful symptoms. Indeed, since many are also able to produce substances of biotechnological interest, they may protect the plant from insect attacks and diseases. The date palm, Phoenix dactylifera (Linnaeus) is a tree which has been known in Saudi Arabia for thousands of years as a staple food. The aim of the present work was to investigate the inhibitory activity of crude extracts of the fungal endophyte Cochliobolus spicifer (Nelson), isolated from the date palm, against Aedes caspius (Pallas) and Culex pipiens (Linnaeus) larvae. In addition, histological changes were determined in the digestive system of treated third instar larvae. The data showed that C. spicifer interfered with the developmental cycle of the mosquito, and had its strongest toxic effect (with 100 % mortality in third instar larvae) at concentrations of 300 ppm. This compound did not show toxicity to zebrafish. The third instar larvae treated with the active fraction showed cellular destruction and disorganization, cell spacing, and vacuolization of epithelial cells in small regions of the midgut. To the authors' knowledge, this is the first study to report the isolation of endophytic fungi C. spicifer from date palm trees (P. dactylifera). The endophytic fungal extract of C. spicifer proved to be a strong candidate for a natural, safe, and stable phytolarvicidal to be used in population control of Ae. caspius and Cx. pipiens.