August 27, 2025, 9:02 am | Read time: 5 minutes

Bti is the weapon against mosquitoes. The abbreviation stands for Bacillus thuringiensis israelensis, a bacterium that dissolves the gut wall of mosquito larvae. This is done by a protein released from the bacterium when water is added. The mosquito larvae ingest the protein and die due to gut damage.

Is Bti Safe for Humans?

“Bti belongs to the group of biocides, so it works against pests,” explains environmental scientist Carsten Brühl from the Rhineland-Palatinate Technical University of Kaiserslautern-Landau (RPTU). “Bti is particularly effective against mosquitoes and flies.” For humans, the bacterium is completely harmless.

Mosquitoes are primarily nuisances. They serve as a valuable food source for many animals, such as fish, birds, and bats. Due to global trade and travel, as well as climate change, more exotic species like the Asian tiger mosquito have now settled in Germany. In rare, exceptional cases, it can also transmit diseases to humans when it bites.

Otherwise, the biting insects are simply annoying during barbecues or other garden activities. Therefore, many private garden enthusiasts want to get rid of the little pests—which announce their approach with a loud buzzing—by any means necessary.

Bti Tablets for Smaller Water Areas

The Bti tablet promises just that: an end to the mosquito plague. The tablets are suitable for local use in the garden, such as in rain barrels, watering cans, birdbaths, or other containers where smaller amounts of water regularly accumulate. The water area and thus the breeding ground for mosquitoes should definitely not be too large. Garden ponds are generally not a problem, as they usually contain fish, which are predators of mosquitoes.

One Bti tablet is sufficient for about 50 liters of water. It can be dissolved in water beforehand and then added to the container or placed directly in the rain barrel or watering can. The duration of effectiveness is stated to be about two weeks. After that, the procedure must be repeated for all potential areas where water stands for a longer time.

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Effectiveness of the Tablets Controversial

However, it remains questionable whether the Bti tablets will actually keep one’s garden mosquito-free. The effectiveness is undisputed, “but a garden owner would have to regularly place tablets in appropriate smaller water areas or puddles during the main breeding season of mosquitoes from April to September,” says the environmental scientist. Because once the mosquitoes are buzzing around, it’s already too late.

Manufacturers therefore recommend the communal use of Bti tablets. Neighbors in urban residential areas or allotment gardeners in garden clubs could team up and use the tablets to curb mosquito swarms. It will probably never be completely successful, as water also collects in public drains, which female mosquitoes then use as a place to lay their larvae. Moreover, just a few outliers who do not participate in the neighborhood mosquito control can allow the insects to continue to multiply.

Since the beginning of the year, there has been a hurdle in Germany: Bti tablets may only be dispensed after consultation with qualified and trained personnel due to a change in the biocide regulation.

The tablets can also be purchased online. Usually, there is a note to leave a phone number for a consultation. Other online retailers have produced consultation videos that replace the personal conversation. This is considered an approved substitute for personal consultation by the relevant authorities.

Free Alternatives

In such a video, it is then reminded to explore other options before using Bti tablets. The alternatives are indeed simple, such as covering rain barrels or regularly emptying collected water into other containers. This does not seem to be particularly labor-intensive. “In case of doubt, a drop of dish soap is enough,” says environmental scientist Carsten Brühl from the RPTU in Landau. “The dish soap reduces the surface tension, so the larvae cannot hold on to the water surface.”

Therefore, the expert advises trying alternative methods before using Bti tablets. They are at least as effective and also more cost-effective. Bti tablets for multiple treatments of a rain barrel are available from eight euros in stores. Whether this is a worthwhile investment is up to each individual to decide. Especially in urban areas, where people live close together, the effect is likely to remain limited.

In regions with a high mosquito population, like the Upper Rhine, Bti has already been used in other forms and on a large scale for some time. With the number of mosquitoes there, it’s no longer enjoyable to spend the evening in the garden by candlelight. Here, tablets are no longer enough to curb the mosquito plague.