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Author Topic: Humans and Pyrethrin?
Member # 83

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We've moved into a new apartment and while we have great water views, we also have some mosquito problems.

There's not a lot of mozzies, just a few a night, but enough. It's mostly our bedroom that's the problem, with windows and doors that don't have insect screens and no air-con: but the fresh sea air is so nice we'd want to have the doors open anyway.

I've been looking into the various solutions which include:

Pyrethrin based air-misters - at around $100, these are wall-mounted things which automatically send a puff of Pyrethrin at pre-set intervals. All the manufacturers claim this is sufficient to keep insects at bay.

Question: anyone have any experience with these? Do they work? And is Pyrethrin safe to be puffing into the air around humans?

'Bug eaters' - they attract bugs via lights and C02 and then suck them into a tray which either dehydrates or drowns them. About $200

Question: Do these work to attract bugs? If so, would we wind up with more than we bargained for!?!?

Mosquito Nets - this is obviously the most simple. Prices range from around $70 - $300.

Question: Are there any particular precautions you need to take when using nets? Do you get caught up in them and rip the whole thing from the roof?

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Member # 6776

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Can you add screens?

Mosquitoes are extremely dangerous because of the diseases they carry, as I'm sure you're aware. Screens on the windows are fairly cheap and work great. I would recommend those if it's possible to get them.

I've never used a net but the thing that confuses me about them is that they only work when you're under them, and there would be a definite possibility of trapping some mosquitoes with you inside the net. I'm not sure if they can prevent all the bites.

I heard an interview with a mosquito expert once, and the thing that impressed me most is that the interviewer asked him at the end what he would do if he were falling asleep at night and heard the whine of a mosquito in the room with him. He answered that he would turn on the light and kill it before going back to bed. That really impressed me. After scares from West Nile and so many other things, I don't think I want to get bitten even once.

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Member # 2393

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Pyrethrin is an insecticide. It's an organic insecticide (derived from pyrethrum daisies), but it's still toxic. (I think calling something an insecticide is misleading advertising, it's more accurate to call it a biocide -- even if it's targeting insects, it's still going to affect other creatures too.)

Here's a link to a link about its use in agriculture. Relevant bits:

Reentry interval (REI) and pre-harvest interval (PHI):
The EPA Workers Protection Standard requires a minimum of 12 hours before reentering a treated field


Effect on human health:
Acute Toxicity: Compared to many other insecticides, pyrethrum is relatively non-toxic to humans and therefore only carries the signal word CAUTION. However, care is warranted.

Rats and rabbits are not affected by high dermal applications. On broken skin, pyrethrum produces irritation and sensitization, which is further aggravated by sun exposure. Absorption of pyrethrum through the stomach and intestines and through the skin is slow. However, humans can absorb pyrethrum more quickly through the lungs during respiration. Response appears to depend on the pyrethrum compound used. Inhaling high levels of pyrethrum may bring about asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, lack of coordination, tremors, convulsions, facial flushing and swelling, and burning and itching sensations (Extoxnet 1994).

The lowest lethal oral dose of pyrethrum is 750 mg/kg for children and 1,000 mg/kg for adults. Oral LD50 values of pyrethrins in rats range from 200 mg/kg to greater than 2,600 mg/kg. Some of this variability is due to the variety of constituents in the formulation. Mice have a pyrethrum oral LD50 of 370 mg/kg. Animals exposed to very high amounts may experience tongue and lip numbness, nausea, diarrhea, lack of coordination, tremors, convulsions, paralysis, respiratory failure, and death. Recovery from serious poisoning in mammals is fairly rapid (Extoxnet 1994).

Organ Toxicity: In mammals, tissue accumulation has not been recorded. At high doses, pyrethrum can be damaging to the central nervous system and the immune system. When the immune system is attacked by pyrethrum, allergies can be worsened. Animals fed large doses of pyrethrins may experience liver damage. Rats fed pyrethrin at high levels for two years showed no significant effect on survival, but slight, definite damage to the livers was observed. Inhalation of high doses of pyrethrum for 30 minutes each day for 31 days caused slight lung irritation in rats and dogs (Extoxnet 1994).

Fate in Humans and Animals: Pyrethrins and their metabolites are not known to be stored in the body nor excreted in the milk. The urine and feces of people given oral doses of pyrethrum contain chrysanthemumic acid and other metabolites. These metabolites are less toxic to mammals than are the parent compounds. Pyrethrins I and II are excreted unchanged in the feces. Other pyrethrum components undergo rapid destruction and detoxification in the liver and gastrointestinal tract (Extoxnet 1994).

Chronic Toxicity: Overall, pyrethrins have low chronic toxicity to humans and the most common problems in humans have resulted from the allergenic properties of pyrethrum. Patch tests for allergic reaction are an important tool in determining an individual’s sensitivity to these compounds. Pyrethrum can produce skin irritation, itching, pricking sensations and local burning sensations. These symptoms may last for about two days (Extoxnet 1994). Cox (2002) reports more serious chronic effects, including circulatory and hormonal effects.

Casida and Quistad (1995) performed 90 day feeding tests on animals. They found no effects at 1000 ppm or less on rats, none at 300 ppm or less on mice, and none at 600 ppm or less on dogs.

Reproductive Effects: Rabbits that received pyrethrins orally at high doses during the sensitive period of pregnancy had normal litters. A group of rats fed very high levels of pyrethrins daily for three weeks before first mating had litters with weanling weights much lower than normal. Overall, pyrethrins appear to have low reproductive toxicity (Extoxnet 1994).

Teratogenic Effects: A rabbit reproduction study performed showed no effect of pyrethrins on development of the offspring (Extoxnet 1994). Casida and Quistad (1995) found that in rats, there were no teratogenic effects at feeding doses of up to 600 mg/kg/day. According to the Agency for Toxic Substances and Disease Registry, part of the US Center for Disease Control, “There is no evidence that pyrethrins or pyrethroids cause birth defects in humans or affect the ability of humans to produce children” (ATSDR 2001).

Mutagenic Effects: None observed in salmonella, rat primary hepatocyte, or Chinese hamster ovary cell tests (Casida and Quistad 1995).

Carcinogenic Effects: “There is no proof that pyrethrins or pyrethroids cause cancer in people. Pyrethrins and pyrethroids do not appear to cause cancer in animals” (ATSDR 2001). However, Cox (2002) cites several studies indicating the possibility of a connection between pyrethrins and cancer, including one study showing a 3.7-fold increase in leukemia among farmers who had handled pyrethrins compared to those who had not. In 1999, a USEPA memo classified pyrethrins as “likely to be a human carcinogen by the oral route” (Cox 2002). Currently EPA is undertaking a review for pyrethrin, which is scheduled for completion and issuance of a Reregistration Eligibility Decision (RED document) in June 2006. The RED summarizes the risk assessment conclusions and outlines any risk reduction measures necessary for the pesticide to continue to be registered in the U.S. (EPA 2004).

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Member # 83

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Unfortunately we can't put in screens - it's a rental and not really possible on the types of windows.

I'm curious about how practical the mosquito net solution is - I seem to recall from a Douglas Adams book that it's best to wind the nets up until used.

I don't worry too much about mozzies in the rest of the house because:

a) I've never seen them while I'm awake
b) I could kill 'em easily if I could see them
c) there haven't been that many - one or two a night, but enough to wake my partner & I up

The Pyrethrin sounds pretty safe. The dispenser I'm looking at takes a 305g cannister and it takes 8 weeks, dispensing every seven minutes, to deplete it.

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Member # 1115

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Originally posted by Tatiana:
After scares from West Nile and so many other things, I don't think I want to get bitten even once.

But...that's not really practical, is it? I mean, I like to minimize the number of mosquito bites that I get, and I'm lucky in that I don't smell particularly appetizing to mosquitos, but I don't think I've ever gone an entire summer without being bitten a few times.
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Member # 2199

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Are you talking about just leaving sliding doors open, like ones that open out on a deck facing the same or something? Or are you talking about regular windows?
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Member # 83

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There's a big wooden sliding door plus two sets of 3 vertically aligned 'wind-out' windows (hinged at the top with the winder and chain at the bottom).

Here's a pic from the bedroom that will probably illuminate things a little. (Sydney Harbour, for anyone who's wondering - the bridge is just out of shot around to the right)


We leave them all open because it's pretty hot and the nice sea breeze is extremely enjoyable.

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Member # 7039

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Wow. That place is beautiful.

I'd suffer the mosquitos to live there.

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Member # 83

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Thanks, we're pretty happy with it, mosquitos notwithstanding!
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Member # 6877

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They do make "temporary" screens that attach and detach without leaving any marks. They're not as good as real screens but somewhat effective.

My mom uses a combination of citronella candles and a bug zapper. It seems to be fairly effective. You can even get citronella torches for longer-lasting use outdoors. She is also extremely, extremely vigilant about standing water, the biggest factor in increase in number of mosquitoes.

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Member # 83

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Yeah, we're certainly careful of that around our potplants, but as you might imagine from seeing the photo, there's plenty of places left after a king tide for water to stagnate and breed mozzies.
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porcelain girl
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(Makes mental note to buy an extra apartment overlooking Sydney Harbor when obscenely rich.)
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