Just ten years ago, our winter squash fields were infested every year by a type of stink bug called, appropriately, the Squash Bug.  Squash Bugs love all kinds of winter squash, spearing both plants and fruit with their probosces and sucking out their juices.  If the infestation were large enough, they would destroy an entire field.
We determined that the bugs like some types of squash better than others.  Certain varieties they love “to death”, others survived their attack.  For more than 15 years, we grew only Butternut, Delicata and Acorn squash.
In the late 1990s, we were approached by a researcher from UC Davis who was trying to establish populations of a fly that parasitizes squash bugs.  He had succeeded on farms in New York and was hoping to do the same in our area.  He released thousands of the flies over several years.
It was easy to find evidence of success:  if you picked up a squash bug, you could quickly see whether or not it had a fly egg attached to its stomach.  The egg would hatch, the larvae would enter the squash bug, and after eating the bug from the inside, a new fly would emerge.
In Entomology this is called “Biological Control” — identifying a specific parasite for a specific pest and then introducing it on a large scale as  a way of keeping pest populations from getting too big.  Most invasive insect pests succeed because their native predators are not present in their new environment.
If a biological control effort is too successful, the pest will be wiped out, eliminating the host for the parasite.  Then the control must be reintroduced every time the pest shows up again.  Biological control programs must also take care not to inadvertently introduce another new pest into an ecosystem, although this tends to be more of a concern when they are looking for a biological agent to control an invasive weed.
For the first few years after the predator fly was introduced on our farm, there were still tons of squash bugs each year.  But there also tons of the flies, at least judging by how many squash bugs were parasitized.  But over the years, we starting seeing fewer and fewer squash bugs.
Out of all the squash we’ve ever grown, the Red Kuri and Blue Ballet varieties were the most susceptible to the squash bugs.  There was no point in growing them.  So we definitely went out on a bit of a limb this year by planting both.  Through the growing season, I tried and tried to find a squash bug in the field, no luck.  I just hope there were enough of them out to keep the population of the flies alive for another year.
Successes like this one are extremely rare — close to 100% control of a pest.  But they are the Holy Grail for researchers who work on them.  There are a dozen invasive insect pests right now that are causing major problems for farmers in California, and they are looking for biological control agents for all of them.  Even a single victory will make a huge difference, especially for organic agriculture.