Mosquito Prevention in the Home and Garden

‘Hello: I was just reading your article and it is very informative. Question:   I have a fountain that I have on a timer to run for 12 hours a day, and I want to know if this is sufficient to deter mosquitoes from breeding in the water? Do they lay eggs during the day or at night? Let me know what you think.

Thank you, Lori’


Mosquitoes are a concern whether living in Bali permanently or even if you’re just passing through or on a short holiday for a few days. While people commonly worry about unexpected death by car accident, or even more unlikely situations such as lightning strikes, shark attacks etc., it is in fact the mosquito that has likely killed more people than anything else – even more than all the wars combined throughout history.

It is estimated that the little buggers kill more than 700,000 people a year and account for almost 20% of the of the infectious disease burden worldwide. What makes them so dangerous is their capacity to transmit viruses and other parasites that can cause debilitating and often fatal diseases.

Every year, it is estimated that malaria alone kills 400,000 people (mainly children) and incapacitates another 200 million for weeks and months. Other mosquito-borne diseases include dengue – 50 to 100 million cases per year worldwide. Deadly yellow fever which has a high mortality rate, and Japanese encephalitis – which can be vaccinated against yet still results in more than 10,000 deaths per year.

Another lesser known yet just as nasty virus spread by mozzies is chikungunya. Whilst less publicised it can be every bit as bad as dengue – I know because I’ve caught chikungunya during an outbreak in Bali back in 2007. The result was bed ridden, fever, nausea and a crushing headache for days right behind the eyeballs – I also lost 10 kilos in seven days, and as for how that happened? Well… I’ll leave that one for you to figure out!

In regard to dengue the biggest worry is catching it more than once as there is no accumulated antibody effect and it’s actually more likely to be fatal if you catch it a second time round and also more likely to be more a danger to adults than young children. Malaria they say doesn’t exist in Bali – but hey I remember that a few years ago rabies didn’t exist here either when I got bitten by a dog…but that’s a story for another day. Malaria is definitely a danger on many islands throughout Indonesia so always check before you travel, particularly from Lombok to the east.

So back to the garden, water features and the home….it is definitely a good idea to keep mosquitoes out of gardens and living areas as best we can. In my experience dengue and chikungunya are the main culprits that you should be worried about in Bali, and Japanese encephalitis is also known to be prevalent. To prevent mosquitoes breeding obviously you need to pay attention to stagnant water sources, yet an often overlooked aspect is just general clutter. Over grown gardens, piles of rubbish, even piles of clothes on the bed are places that mosquitoes will like to hide in and around the house.

Adult mosquitoes usually rest indoors in dark areas like closets, under beds, behind curtains etc but like I’ve said clutter will attract more of them. Again, I can only speak from my experience, I know that a well airconditioned house or a strong fan also acts an effective deterrent to the little nasties.

Just a few mosquitoes per household can produce a large dengue outbreak, and whilst you may be able to effectively keep them out of the house we cannot stay indoors forever – and during the wet season Bali can feel like one giant water feature! So what’s the answer?

The standard personal precautions should always be taken – use insect repellent, cover exposed limbs, use citronella candles and mosquito coils under tables and mosquito nets indoors.

As to whether they lay eggs by day or night…well it is more complicated than that. They usually deposit their eggs at night, and can lay them about every third night, up to three times. The dengue carrying mosquito will often lay on the side of your water filled container anticipating a rise in the water level, the eggs could stay active there for months. Though most mosquitoes lay their eggs directly into water, others lay their eggs near bodies of water in anticipation of the water level rising. Eggs will hatch into larvae within 24 to 48 hours of becoming submersed.

To deter mosquitoes from laying eggs in your water feature the first step would be running the pump from dusk until dawn, yet this is still no guarantee. You could purchase a solar powered fountain to pick up the slack during daylight hours – they are quite cheap to buy online. Depending on the size of the water feature a mosquito net draped over the top during the day could be an effective option.

My preferred strategy would be to introduce predator fish into the water in combination with all of the above.

An aerator, pump, or fountain would need to be extremely aggressive in the amount of water it churns through to minimise mosquitoes and their larvae. A pond of any size, even when well agitated, will usually have at least one zone that is calm enough to allow mosquitoes to lay their eggs, and that’s where the fish come in. Most small fish species eat mosquito larvae, including the aptly named mosquito fish, goldfish, minnows, tetras and guppies. Mosquito fish are the best-known for their ability to control mosquitoes and thrive in a wide variety of weather conditions. A single mosquito fish can eat up to 100 larvae in a day.

For larger ponds you can use mosquito dunks in the water (which is like a big tablet) that contains a bacteria called bacillus thuringiensis, which disrupts the mosquito breeding cycle and also harmless to children, pets, birds, plants, or any fish you might have.

Other tactics to consider?

Eliminate standing water from the immediate garden and household areas. Common breeding grounds are buckets, plant trays and guttering filled with rain water. Overturn and clean up water filled containers and unblock your roof gutters and ensure stormwater drains run freely to prevent breeding grounds for mozzies. Remember these are all harm minimisation strategies, unfortunately you can’t have the tropics without the mosquitoes, or your cake and eat it too!


Dr. Kris

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