Abstract

Mosquito Control is important to the community because of the vector potential that exists from mosquitoes in transmitting diseases and the annoyance factor in disrupting outdoor activities. The vector potential of mosquitoes stems from the female's bloodsucking habits. Various mosquito species are capable of transmitting malaria, dengue, yellow fever, filariasis, encephalitis, chikungunya, and Zika viruses and other diseases. Apart from being a nuisance to the public by affecting labor efficiency, depreciation of real estate values, and interference with outdoor activities, they also affect the health of livestock, pets, and wild animal population. Several techniques are used for mosquito control like chemical control, biological control, source reduction, environmental control, genetic control, traps and personal protection. Shampoos being regularly used, the effluent containing the same is being discharged into the open environment. The present study attempts to investigate the larvicidal effects of different shampoos (a means of chemical control) on mosquito larvae. Toxicity studies were carried out using the serial dilution method and LC₅₀ was estimated for each of the shampoo type (Superia, Clinic Plus, Dove, Sunsilk) at 24h interval for five days. A comparison of the lethal effect of these shampoos at specific concentrations (0.1, 0.15, 0.2, 0.25, 0.3 and 0.4) was also done. The study reveals that Superia shampoo has the best larvicidal properties (0.1mlL¹) compared to Dove (0.15ml L^-1), Sunsilk (0.15ml L^-1) and Clinic Plus (0.2ml L^-1). The low LC₅₀ value for a particular shampoo could be attributed to the special combination of ingredients used in its preparation which could be employed for mosquito control. An extensively used cosmetic product could be turned into an effective vector control product with further research in the area.

1. Introduction

Mosquitoes constitute the most important single family of insects from the standpoint of human health. Due to their high potential to exploit even adverse environmental conditions, mosquitoes can rapidly increase their population ¹. Mosquitoes transmit more diseases than any other group of arthropods and affect millions throughout the world.

Approximately, half of the world’s population is at risk of mosquito-borne diseases, with the highest-burden for socioeconomically disadvantaged populations. Urbanization, globalization, climate change, and land-use shifts have each contributed to the re-emergence and expansion of mosquito-borne diseases ^{2, 3}.

Mosquito borne diseases are prevalent in more than 100 countries across the world, infecting over 700,000,000 people every year globally and 40,000,000 of the Indian population. WHO has declared the mosquitoes as “public enemy number one” ⁴ as they act as a vector for most of the life-threatening diseases like malaria, yellow fever, dengue fever, chikungunya fever, filariasis, encephalitis, West Nile virus infection, Zika virus fever, etc., around the globe ^{5, 6, 7, 8}. They not only can carry diseases that afflict humans, but also transmit several diseases and parasites to birds, dogs, horses, etc. ⁹ and contribute significantly to poverty and social debility in tropical countries ¹⁰. Therefore, the control of mosquitoes is an important public health concern around the world.

To prevent proliferation of mosquito borne diseases and to improve quality of environment and public health, mosquito control is essential. Chemical, biological, physical, organic and genetic control measures have been employed to control the vector population ¹¹. Environmental management (through reduction or removal of mosquito breeding sites) is being used along with chemical or microbiological ovicides, larvicides, and pupicides. But these are only moderately effective, due to resistance arising from physiological (e.g., insecticide resistance) ¹² and behavioral changes (e.g., mosquitoes change their blood-feeding times in response to bed nets). Chemical interventions also have unintended effects on non-target insects, including pollinators ^{2, 9, 13, 14, 15, 16, 17}.

Mosquito larval control using chemicals and biological agents is of paramount importance in vector population and disease incidence reduction ¹⁸. Increasing vector control efforts targeting larval sources is of high priority as larvae are relatively immobile compared to adult mosquitoes. Controlling mosquitoes using larvicides has shown a great impact in larval mortality in field situations ^{19, 20}.

Most chemical control methods face the challenge of tolerance development of mosquitoes against the given control methods ²¹. Hence, the current control methods have fallen short of eliminating the disease burden and there is a critical need for safe, sustainable approaches to reduce the burden of mosquito-borne pathogens.

In this scenario, we intend to explore the larvicidal potential of daily use cosmetic product- shampoo, which is being released as effluent into the aquatic environment on a regular basis.

2. Material and Method

The experiment was carried out in 1L bottles. Control and test samples were run simultaneously. Into each bottle containing 1L water, 6 mosquito larvae were introduced. All bottles except the ‘control’ contained specific concentrations of different Shampoos. Toxicity studies were carried out using the serial dilution method and LC₅₀ value was estimated statistically using the mortality counts mosquito larvae in the dosed containers during 24h interval for five days. The effect of different concentrations (0.1ml, 0.15ml, 0.2ml, 0.25ml, 0.3ml and 0.4ml) of Clinic plus shampoo, Sun silk shampoo, Superia shampoo and Dove shampoo were studied for a period of 120h. The specific quantity of shampoo was added to the test bottles using 1 ml pipette. Mosquito larvae were monitored and counted daily manually using a magnifying glass for better visibility. For each dose five replicates were run at a time. Data was collected during 24h, 48h, 72h, 96h and 120h. Dead larvae were removed and developmental progress to the pupal stage was noted. Resulted were tabulated and interpreted.

3. Result

A comparison of the lethal effects of Clinic plus, Sun silk, Superia and Dove shampoos was done at specific concentrations (0.1, 0.15, 0.2, 0.25, 0.3 and 0.4) for a 120h period.

Figure 1 clearly shows that Superia shampoo has larvicidal effect even at a low concentration of 0.1ml L^-1. All the shampoos considered for the study (Clinic plus shampoo, Sun silk shampoo, Superia shampoo and Dove shampoo) has somewhat similar effect at the concentration of 0.4ml L^-1. At a concentration of 0.1ml L^-1, only Superia shampoo brings about 50% mortality of the mosquito larva in the test samples during 120h study period. Above the concentration 0.25ml L^-1, all four shampoos under the present study causes 50% mortality in the mosquito larva test sample. Figure 1 suggests Dove shampoo to have the least larvicidal potential even at 0.4ml L^-1 concentration.

Figure 2 suggests that during the first 24h period, for a concentration upto 0.25ml L^-1 the only shampoo that exhibited larvicidal effects was Superia shampoo. Again, in the next 24h period (48h), only Superia shampoo was effective in producing larval mortality upto a concentration of 0.2ml L^-1. Maximum lethal effect of all the shampoos under study was evident between 96hr-120h period.

The shampoo composition comparison chart (Table 1) shows that though there are some similar ingredients (Mica, titanium dioxide, water, fragrance, CAPB, PEG, dimethiconols and Guar hydroxypropyltrimonium chloride in the shampoos, some unique compounds (CTAC, Amodimethicone, Sodium Laureth Sulfate, SodiumBenzoate, Phenoxyethanol, Benzyl Salicylate, Hexyl Cinnamal, Limonene, Linalool, Sodium Ascorbyl Phosphate, Alpha Olefin Sulphonate, Hibiscus and Brahmi extracts) are also present which could account for the difference in action of the shampoos.

4. Discussion

Toxicity studies conducted during the part of this study revealed that shampoos can be used as a measure to control mosquito larvae. Though the LC ₅₀ values of the shampoos differed slightly (Clinic Plus- 0.2ml L^-1, Superia - 0.1 ml L^-1, Dove- 0.15ml L^-1, Sunsilk- 0.15 ml L^-1) all of them proved to be potential candidates for an effective larvicide. Figure 1. Shows that all the shampoos have a progressive trend when the dose dependent larvicidal effect of Clinic Plus, Superia, Dove and Sunsilk was analyzed. Though, all the 4 shampoos under study suggests having larvicidal effects, Superia shampoo has lethal effects on the mosquito larvae even at a low concentration of 0.1ml L^-1.

During the first 24h period, the only shampoo that exhibited larvicidal effects was Superia shampoo (Figure 2) and it shows larvicidal effects at 0.1ml L^-1 (Figure 1). Superia claimed to be a natural shampoo is found to have stronger larvicidal effect than the other 3 shampoos considered for the study. This gave way to the shampoo composition analysis (Table 1). When water, fragrance and CAPB is a common ingredient in all 4 shampoos used, Mica, titanium dioxide, PEG, dimethiconols, Guar hydroxypropyltrimonium chloride and Tea-Dodecylbenzenesulfonate are present only in Dove, Sunsilk and Clinic plus shampoos. Of these, PEG has reported to have larvicidal effect on mosquito larva ²² and titanium dioxide is effective in bringing about oxidative stress, inflammation, genotoxicity and even carcinogenesis ²³, unsure of the larvicidal effects though. Whereas the mica, dimethiconols, Guar hydroxypropyltrimonium chloride and Tea-Dodecylbenzenesulfonate are regarded as less toxic or inert substances ^{24, 25, 26, 27}.

Several ingredients like CAPB, Sodium Laureth Sulfate, Dimethoconol, Dimethicone, Cetrimonium chloride, DMDM hydantoin, Benzyl Salicylate, Limonene, Linalool, Hexyl Cinnamal, Alpha Olefin Sulphonate, Citric Acid, etc used in these shampoos are known to have emulsifying, surfactant properties detrimental to the environment ^{28, 29}. Sukkanon et.al. ³⁰ states that silicone-based surfactants are becoming popular for mosquito control in Thailand. Surfactants interfere with the larval respiration and thereby act as a larvicide. Bilal et.al ³¹ discussed the efficacy of limonoids as larvicide which again forms an ingredient of the shampoos under study.

Superia shampoo, inspite of containing the least number of synthethic/ artificial ingredients (Table 1), proves to be most effective larvicide when compared with Dove, Clinic Plus and Sunsilk shampoo. The larvicidal, antimicrobial, antiparasitic properties of Hibiscus and Brahmi extracts, which form the key ingredients of Superia shampoo, could account for the larvicidal action of Superia shampoo ^{32, 33, 34}.

The findings of this study have demonstrated that the mortality of larvae shown by shampoos especially Herbal shampoos is worth for further studies in open water bodies. More studies have to be done to find out the effect of other variables in semi field before small scale field trials.

5. Conclusion

We are aware that mosquito control is necessary, but it is difficult to control the adult mosquitoes when compared to the immature stages as they are restricted to their habitats found in an aquatic environment ². Shampoos being regularly used, the effluent containing the same is being discharged into the open environment. The study, though a preliminary study, suggests that all the shampoos considered for the present study are effective in controlling mosquito larva and thereby by considered in environmental management. An extensively used cosmetic product could be turned into an effective vector control product with further research in the area.

References