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Researchers have looked at it and found that
neem oil is non toxic for example to spiders, butterflies and to insects that pollinate plants. Scientists looked especially at
how neem oil affects honey bees, since bees do eat plant matter, the pollen.
That's why reasearchers studied what happens if flowers get sprayed with
neem oil.
And what they found is very reassuring. To see any effect the scientists had to use very high concentrations of neem. They used a lot more than you would ever use for pest control.
Only if they constantly hit the flowers with a very concentrated
neem oil spray did they see an effect, and only in some small hives (medium sized and larger hives were still unaffected.)
What happens is that the bees carry contaminated pollen back to the hive and feed it to the brood. In the small hives some of the new bees could not emerge from their cells (Schmutterer and Holst, 1987).
Weekly use of a
neem oil spray at a normal concentration (0.5% - 2%) will not hurt honey bees at all.
You can also rest assured that
while neem hurts aphids, whiteflys and the like, it does not harm ladybugs and other predators that eat the aphids, or the tiny wasps that are parasites on many pests.