Coagulation-Flocculation: A potential Application for Mosquito Larval Source Management (LSM) with No Insecticide Resistance

Abstract

Background: Mosquito control is an essential step to eliminate mosquito-borne diseases. Larval mosquitoes have a more limited home range and lower resistance to adverse environment than adults, thus can be ideal targets for vector control in some cases. Coagulation-flocculation technology, which could be used for water treatment in breeding sites of several vector mosquito species, can significantly change both the distribution of organic particles and surface sediment characteristics in water environment. The aim of this study was to explore the effect, principle and possibility of using coagulation-flocculation technology in immature mosquitoes killing.Method: In laboratory, chlorine-free tap water was treated with Poly Aluminum Chloride (PACl, sewage treatment using). The oviposition preference of gravid Culex pipiens pallens, the hatching of mosquito eggs and the survival amount of mosquito larvae were observed, and the pupa amounts were recorded each day.Results: Coagulation-flocculation treatment could improve the oviposition preference of Culex pipiens pallens to some extent (compared with ordinary chlorine-free tap water), but not significantly (p=0.345). After treatment, mosquitoes laid eggs in chlorine-free tap water were 31.88% more than those laid in untreated water. Coagulation-flocculation affected the larvae’s survival by physical means: Ⅰ) alum floc layer increases the difficulty of larvae foraging, leads larvae starving to death; (Ⅱ) the little floc particles adhere to the surface of larvae, which stops larvae from floating upward to breathe. As a result, the alum floc layer had a good killing effect on the mosquito larvae, presented the half lethal time (LT50) of 2d, the 90% lethal time (LT90) of 8.7±7.3 ~ 14±4.5 d, and the pupation rate of 0 ~ (6.5±0.5)%, respectively.Conclusions: PACl coagulation-flocculation produced lots of alum flocs, which may attract more gravid mosquitoes for laying eggs, and was shown to be highly active against 1st~2nd instar larvae. The principle of this technology illustrates this method won’t develop insecticide resistance. In this study, coagulation-flocculation technology is considered to be a new potential approach to a sustainable, low-impact and low-cost mosquito control method.