Phototoxicity of eosin yellow lactone and phloxine B photosensitizers against mosquito larvae and their associated predators

Abstract

Mosquito larvae and their predators were surveyed from different breeding sites in El-Fayoum Governorate. The physiochemical characters of water and environmental factors that effect on mosquito larvae were studied. Biochemical and toxicological effects of the two photosensitizing compounds; eosin yellow lactone and phloxine B (xanthene dye) were evaluated against the third instar larvae of the most dominant mosquito species and their predators. The surveyed results revealed the occurrence of six mosquito species in the study area: one aedine, Aedes caspius, two anopheline, Anopheles pharoensis, An. sergenti, and three culicines, Culex pipien, Cx. antennatus, and Culiseta longiareolata. The most dominant species was Cx. pipiens with a total number of 3571 larvae followed by Ae. caspius and An. phareonsis with a total number of 670, 452 collected larvae, respectively. The two commonly collected predators were Pantala flavescens (Odonata) and Caenis macrura (Ephemeroptera) naiads. The results explained that both eosin yellow and phloxine B can be used as larvicide. However, eosin was more efficient than phloxine against Cx. pipiens with LC₅₀ equal to (0.025 and 0.053 ppm) and An. pharoensis (0.023 and 0.016 ppm, respectively. On the other hand, the phloxine was more effective than eosin against Ae. caspius (0.016 and 0.024 ppm, respectively. Also, the results investigated that phloxine was more efficient than eosin against Cx. pipiens in dark and there was a significant difference between their toxicity in sunlight and in the absence of direct light. In addition, phloxine was less toxic against P. flavescens than eosin with LC₅₀ of 1.822 and 1.044 ppm, respectively) and the mayfly (C. macrura) was more sensitive to the both photosensitizers with LC₅₀ equal to 0.003 and 0.006 ppm for eosin and phloxine, respectively. The biochemical studies indicated the increasing in the levels of glutathione S-transferase after treatment with eosin and phloxine and there is a significant decrease in peroxidase levels after treatment with both eosin and phloxine.