The influence of plant oil extracts Allium satvium , Citrus limon and Bacillus thuringiensi israelensis on the biology and histology of Culex pipiens larvae (Diptera: Culicidae)

Abstract

The extensive use of chemical pesticides are inducing resistance by insect pest beside residue contamination of human food and environmental pollution, so the present study included biological control of 4th instar Culex pipiens (L.) (Diptera: Cuclidae) by using plant oil extracts (Allium satvium and Citrus limon) and entomopathogenic bacteria (Bacillus thuringiensis israelensis). The results showed that the fourth instar C. pipiens (L.) was highly susceptible to Bacillus thuringiensis israelensis followed by Citrus limon and Allium sativum. In all case, appositive relationship between the time of exposure and mortality percentage of larvae was recorded. Histopathological studies revealed there was a highly damage in the midgut epithelial cells. The tissues of gut, muscle, fat body and cuticle were the most severely damaged by the treatment. Also, the destructive damages described in the investigation depend mainly up on the time of exposure and the dosage. The ultrastructural findings of the 4th instar C. pipiens (L.) showed the separation of midgut epithelial cells from the basement membrane. Moreover, separation of columnar and goblet cells together with vacuolezed appearance was demonstrated. The nuclei of columnar cells were clumped into large irregular appearance and destruction in microvilli.