Neem oil for insect control

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A few weeks ago now I was watering the garden just after dark, torch in one hand, hose in the other, when I was attacked by a swarm of mosquitoes (mozzies).  I could feel them biting me, but there wasn’t much I could do with both hands in use and I really needed to finish watering.  When I came inside I found that I had several bites on each leg between the top of my gumboots and the bottom of my shorts.  These proceeded to itch, swell and annoy me for several days.

At this time of year, when the mozzies start biting, as I do have such a terrible reaction to the bites, I usually reach for my bottle of conventional insect repellent, typically containing DEET (N,N-Diethyl-meta-toluamide, mmm mmm), and smelling terrible.  A quick search of google shows that the safety of DEET is questionable.  Yes the US EPA and the insect repellent companies say is ok, but plenty of other sources say that its not.  I suspect that it is a chemical with long-term effects that would be very difficult to measure or prove one way or the other, so I’d like to avoid it if I can find an alternative.

I asked on my facebook page if anyone knew a better way to prevent mozzie bites and I had a few suggestions including neem oil, tea tree oil and taking vitamin B.  Again I couldn’t really find a definitive answer on the Vitamin B idea, but it can’t hurt to increase Vitamin B levels, so I bought a multi B tablet to take.

Neem oil, however, is very highly recommended (for example), so I thought it was worth a try.  I ordered a small bottle of neem-based insect repellent.  This product contained organic pure neem seed oil, rose geranium oil, tea tree oil, eucalyptus oil, citronella ceylon oil, lemon myrtle oil, lavender oil, based on pure grape seed oil.  It smells quite nice actually.  I have been using it ever since it arrived, and haven’t had another bite, so it works as well as the DEET-based insect repellent.  I will be testing it in a sandfly area when we go up the coast over Christmas and will let you know what I think.

Since I tried neem oil as an insect repellent, and it worked, I started to wonder what else it would be good for.  It turns out that neem oil has both repellent and insecticidal properties.  The exact nature of all the components of neem oil is not well understood (conspiracy theory: probably because some large chemical companies would suffer if neem oil was more widely used, most of the research seems to focus on synthesising the main component, Azadirachtin, but chances are this is one of those natural products where all the components are important, and isolating the main component will just cause more trouble, eg aspirin). 

Unlike most chemical insecticides that kill by contact with the insect, neem oil works by disrupting the insects’ hormones, so they must ingest the neem oil to be affected.  This means that it only affects insects that bite or chew, and is safe for bees and spiders (and, unfortunately, fruit flies), unless they become coated in the oil.  As the neem oil affects the hormones, only small amounts are required for insecticide use (0.5–1% neem oil in a carrier).  Read more here and here about how it works.

The repellent action of neem oil is less well understood, but appears to work (I am living proof), although its effectiveness seems to depend on the type of mosquito (see here).  As far as I kind find out, slightly higher concentrations (up to 10%) of neem oil are effective as an insect repellent.  I think this explains why beneficial insects are not affected or repelled by the low concentrations used to kill biting insects, however, higher concentrations work to repel all insects (because I don’t want to wait for them to bite me, get sick and then die!). 

Now that I kind of understood how neem oil works, I had a think about how I could use it around our home and farm(s):

• Obviously as an insect repellent on my own skin, but we also use it on the cattle as part of an organic product called “Cattle Coat”, which they self-apply using a backrub at Cheslyn Rise, and we spray onto the tame cattle at Eight Acres. 
• I picked up a hen the other day who was crawling with lice, so I gave her a good spray with a mixture of neem oil in water.  A few days later I checked her again and the lice were gone.  Now I have the spray made up, I check the chickens weekly when I’m feeding them, and give any with lice a quick spray.  I also sprayed inside their cages.
• We usually burn a mosquito coil when we are sitting outside in summer, they contain the other type of nasty repellent chemicals called permethrin, so I’m going to replace that with a diffuser and use the Pesky Protect in that.
• In the garden, I am disappointed that it won’t work on the fruit flies, but I think it will do a good job on the potato leaf beetle; I just have to make up a separate spray bottle at lower concentration.  I got a little over-excited and sprayed the potato plants with the same oil I had been using on the chickens and it was too strong and damaged the leaves.
• When I put away my winter clothes in the wardrobe, I also put a dab of neem oil on a cloth inside the plastic boxes to repel moths.
• Next time I clean out the pantry, I will wipe the surfaces with neem oil to deter cockroaches and weevils (I read that neem leaves can also be used inside containers).

There’s lots of good resources out there, so do some research and let me know what you would like to try (or anything that you have already tried).  Unfortunately this giveaway is for Australia only, but feel free to comment anyway if you’re in another country, just let me know not to put you in the draw.  I will announce the winner next week.