ABSTRACT
Medicinal plants contain numerous bioactive compounds that rendered them potential targets for extensive research to produce novel pesticides against mosquitoes and important vectors of infectious diseases in the world. In this study, the histopathological and biochemical effects of three medicinal plants, myrrh, pomegranate and black seed, were tested against the mosquito Culex quinquefasciatus in Saudi Arabia. Fourth instar larvae were treated with aquaeous extract of each plant separately and the changes in various larval tissues and protein profile of the treated larvae were investigated. The results showed that many tissues suffered major changes due to exposure to plant extracts. The observed changes include rupture and disintegration of midgut epithelium with detachment of cellular membranes. There were vacuolization and swelling of some epithelial cells with the appearance of unknown structures. Other cells appeared devoid of nuclear material, which might be due to fragmentation of nuclear DNA/chromosomes, an important sign of apoptotic cells. Other tissues: Malpighian tubules, muscles, nerve ganglla and fat tissue suffered varying degrees of damage, but lesser than the midgut. Protein analysis showed changes in general protein profile of treated larvae compared to normal larvae. Treatment with plant extracts resulted in loss of protein bands of molecular weights of 2.3 KD and bands between 75 and 212 KD. In all treatments, a group of bands of molecular weights between 9 and 71 KD appeared but with variable profiles, which indicates the loss or gain of one or more band compared to the control mosquito profile. These bands might be metabolic products or fractions of the larger protein bands in response to treatment. These results showed that water extracts of myrrh, pomegranate and black seed affected various tissues and protein products of the mosquito at varying degrees and apparent modes of action. These changes will implicate various physiological processes of the mosquito and could interfere with its life cycle and vectorial capacity for disease transmission. Therefore, more research is needed to determine the specific mode of action and molecular targets in different mosquito stages as well as the side effects on non-targets of each plant extract for the production of novel effective and safe mosquitocidal compounds