Neem Oil is an effective insecticide, and it's pretty benign for humans.
Azadirachtin is the active chemical. You can find the hazard information and other good material at the link below.

Like any other horticultural oil, it should not be used when the weather will be hot.
In dry, windy heat, I've seen leaf and cane damage at temps not a whole lot over 75 deg.

BE SURE that you know which neem oil you are buying.
Some "Neem Oil" has only a low % of Neem extract.

One other caution: Neem Oil DOES have a harmful effect on bees, and may be a contributor to some of the serious problems now being experienced by these valuable critters.
We use it now only sparingly, largely for that reason.

We have not sprayed generally for several years, finding adequate control for the insects in our area without having to do that.
But then, we don't have Japanese Beetles . . .

Jeri

Here is a link that might be useful: Neem Information

Thanks for responding. I have a BIG problem with japanese beetles, thrips, aphids and a bunch of other things that I don't know what they are.

Neem does nothing for JBs.
Olga

"For those seeking a botanical alternative, Neem products such as Azatrol or Neem-Away (Gardens Alive), or Pyola (pyrethrins in canola oil) provide about 3-4 days deterrence of Japanese beetle feeding." Quote from:

http://www.ca.uky.edu/entomology/entfacts/ef451.asp

As an experiment, I tried adding Neem to Wilt-Pruf expecting that the combination would result in a longer lasting deterrent. I did not use controls, etc. but I thought that the combination was effective.

Here is a link that might be useful: University link cited above

Henri, sorry but this didn't work for me. I tried several times and with different brands of Neem (with Azadirachtin). Jbs in my garden considered it as a good salad dressing for rose leaves. Most probably it depends on how high is your JB pressure. When they are in high numbers (hundreds of thousands), JBs can't afford to be picky. Every rose (sprayed with deterrant or not)will be eaten.
Olga

The following is the complete Google Scholar scientific search using the keywords "Japanese Beetle" and neem:

http://scholar.google.com/scholar?q=%22japanese+beetle%22+neem&hl=en&lr=&btnG=Search

Here is a link that might be useful: Complete Google Scholar search

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This last post offends me.

Forensicmom-- Unfortunately, there is no all-purpose insecticide. You have to identify the pests and choose an appropriate control for each. Observe carefully and ask detailed questions on the appropriate GW forum. Read fact sheets for the various plants at the website of your state's ag extension service. These will usually describe the main pests and diseases for, say, tomatoes in Oklahoma.

There are three types of neem insecticide.

The majority of neem oils in garden centers have had the azadirachtin removed. These are labeled "hydrophobic extract of neem." These products may not be functionally different from canola oil or mineral oil; that is, they can't do anything but smother small sedentary insects.

Neem oils containing azadirachtin are labeled "whole neem oil."

Azadirachtin extract is sold separately, and packages will show that term under "active ingredient." You may find it at good garden centers. It is a somewhat systemic chemical that, if ingested or absorbed, prevents all insects from molting through the growth stages. It should not be applied to open flowers because of the danger to bees.

I use a product called Ferti-lome that contains 70%
hydrophobic extract of neem oil, and 30% other ingredients.
I use it mainly for spider mites, but it will also kill
aphids. Don't know about JB's. I know many people will
argue that I'm wrong, but it has also knocked out black spot for me, when nothing else would. I can only find it
at feed and seed stores. It costs $14.99 for a 16 oz. bottle.