Does neem oil hurt honey bees and other beneficial insects?
Insecticides kill insects. That's why they are called insecticides. Usually pesticides make no difference beween pests and beneficial insects.
But neem oil is different.
As explained on the page about neem insecticide, neem oil is not really a knock down, kill-on-contact insecticide like the chemical poisons. Neem must be ingested (eaten by the bugs) to be effective.
If bugs don't eat leaves they don't get hurt. Simple.
In reality it is a little bit more complicated than that, but the fact remains that neem oil is impressive: it really does hurt bad bugs while sparing the good bugs.
Researchers have looked at it and found that neem oil is non toxic for 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 reaseachers 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.
In one field trial researchers collected and counted aphids and their parasites and predators from fields. In the neem treated field there was the same amount of predator activity as in the untreated fields, and the aphids carried even higher numbers of parasites!
As I already mentioned above, the reason is that the beneficial insects don't eat the leaves and so never consume enough neem to be affected.
But you still need to be careful when you spray neem oil in your garden.
Any oil spray can smother and suffocate insects, and in that respect neem oil makes no difference between good and bad bugs.
So when you spray neem oil, please do it first thing in the morning or late in the evening, when the good bugs are least active. That way you won't hit any bees or other beneficial insects directly. The neem oil spray will dry before they land on the plants, and only the insects trying to eat your plants will die.