There are "good" & "bad" nematodes, therefore it's vital you get the correct "good" ones for your particular situation.
According to Wikipedia there are 2 kinds of nematodes from a horticulture perspective:
Keep in mind the "good" nematodes will not kill the actual beetles (get rid of the problem this year). The "good" nematodes will feed on the beetle lava, thus reducing the possibility of experiencing the same beetle problem the following year.
As long as I have been listening to (nearly 4 years now), Mike McGrath from You Bet Your Garden, I can honestly say I've never heard him once warn against the use of "good" nematodes ie possible side effects. Yes, I have heard him warn against "bad" nematodes, that is why I believe it's vital you do your research and get the "good" guys.
For total peace of mind, I would do plenty of research... before deciding on the exact type of "good" nematodes you buy and release into your landscape.
Do you have a horticultural service in Israel you can contact directly and seek their specific local advice, expertise?
If you can wait a few days (probably until sometime next week), I can call and speak with a local (Missouri) registered organic farmer and seek his advise. I know for a fact he grows, apples, apricots, peaches & pears on his property.
Here is what I have been able to find out during the past few days:
- Speaking with a Master Gardener, first they clearly stated they weren't a nematode expert (very! much like myself), but they did say they have never heard of or read anything about beneficial (good) nematodes causing "bad" side effects. Depending on the nematode in question, they do a very! specific job, they do not mutate (change) and start doing something else (be it "good" or "bad").
The above has been my limited experience (I've only used "good" nematodes once), is my understanding from reading up on the subject from an organic gardening approach to controlling unwanted pests, and listening to other people talk on the subject...
Spoke with a garden pest control expert (via the Missouri Botanical Gardens), they basically confirmed what the Master Gardener had told me. They also added that beneficial (good) nematodes isn't a "magic bullet" to pest control, will normally take more than one application, which can become expensive depending on the individual situation, and can take 2 or 3 years before seeing real results.
Garden pest control expert (via the Missouri Botanical Gardens) also referred me to this, "Beetles - Grubs" "general" article on MOBOT.org
Speaking with my local (Missouri) registered organic farmer, he has never used beneficial (good) nematodes as a pest control method. Why? On his size orchard it would be far too expensive to use such a pest control strategy. Instead he uses a product called "Surround™ WP Crop Protectant", which works by protecting the actual fruit on the trees. Since moving to this method of pest control on his fruit tress he has gone from losing up to 70% (really bad years) of his crop to only losing about 20% (per year).
If you're interested in reading a little bit about "Surround™ WP Crop Protectant" the below link contains a small amount of information:
The link goes to the company he buys from (via mail-order).
I think you might also find this, Gardening Naturally with John Dromgoole - Saturday July 23 2011 hr 2, of some interest. Start listening @ 10min:55sec in.
I hope the above proves somewhat helpful and useful to you.