Technically Insecticides kill insects. That said, there are products that are designed to deter insects. Some make the food source unpalatable, some repel, others sheild. The actual insecticides are normally in three formats. Contact poisons which kill on contact, stomach poisons which must be ingested by the insect, and hormones which interfere with reproductive cycle.

Just to kick things off, some insecticides do work on the target organisms' nervous system leading to death. Bt acts by target ingesting it and it's gut is "disabled" and death ensues. There, the depth and breadth of my understanding of your question. Oh wait, I think some insecticides cause the target to dessicate and Surround WP (I think) is an irritant, don't know if it causes death.

Sevin dust's primary active ingredient is carbaryl. This is effectively a contact/ingestion neurotoxin that shuts down the insect's nervous system's ability to self regulate.

Or, in other words, it throws the bug's brain into hyperdrive and stops them from being able to, well stop. You can imagine what that would do to your heart, muscles, brain activity, etc (but its not harmful to vertebrates, just insects). I imagine it would be like the biggest caffeine overdose on the planet.

Although insecticides can be categorized a number of ways, generally they are divided into contact insecticides and ingest insecticides.

Contact insecticides are generally absorbed through the insect's cuticle. By walking on the foliage, the insect absorbs the compound. Since only the compounds most lethal to insects are generally engineered/selected as insecticides, it takes only a very small amount to kill the insect. It would be the equivalent of the nerve agent VX for humans (One milligram on human skin causes death.) Contact insecticides sometimes benefit with a small amount of horticultural oil as an adjuvant which increases cuticle uptake, however oil generally isn't necessary. Most contact insecticides operate on the nervous system and essentially paralyze the life support systems of the insect, or cause over excitement of the nervous system as mentioned above. Contact insecticides can also be ingested by the insect with equal results.

Other insecticides don't work on contact but must be ingested. The mode of action of these insecticides varies. Some (called growth regulators) mimic insect hormones and cause the insect to go through a premature development stage (like molting) before the insect is ready, and cause death. These are considered some of the safest products because they are very specific to the insects being targeted. There are some new insecticides that work by targeting muscle tissue of the insect. Belt and Altacor fall in this category.

Some insecticides, like Imidan, also have repellent activity. Obviously this is useful in that it reduces egg laying on the plant.

Insecticides can also have what's called sub-lethal activity. Intrepid is one such insecticide. It's a larvacide, but will not kill adult insects. However, it does have sub-lethal effects on adults. This means that when an adult female moth absorbs some of the compound, the moth is unable to lay eggs for the rest of her life.

There are strictly repellents like Surround, as Michael mentioned. It's listed as an insecticide with the EPA, but technically it's not, because it doesn't kill the insect.

Wow! Great info. Thnx. I was curious because it would seem the insects could land on the fruit (especially PC) and do a lot of damage, ie lay their eggs before any poison kicked in. But from the sounds of it, these chemicals act very quickly, before they can lay eggs. Amazing

Contact insecticides are generally ovicides as well as larvacides, and adulticides, so that even if the adult was able to lay eggs before it died, the eggs would still absorb a lethal dose of the residue.

"I was curious because it would seem the insects could land on the fruit (especially PC) and do a lot of damage, ie lay their eggs before any poison kicked in."

I use Triazicide for PC, it's a neurotoxin. Their egg laying attempts are really messed up, like they're drunk.
I caught 3 and put them in a container with some of the Triazicide. Most looked like they were dead. The one that didn't had problems. The ones that seemed dead started to wake up after some time but were not healthy and eventually all died for real.

Myk,

I'm curious about your experiment. Can you share some more information?

Did you use concentrate in the container, or dilute? Was the insecticide dry, or was it still wet? How long did it take for the curculios to die?

Anyone have any experience with Pyganic and Plum Curculio?

Olpea,
It was dilute. I had them in a yogurt or cottage cheese container with some plastic wrap over the top. Pulled the plastic wrap back and sprayed so it didn't dry.

From failing memory;
I was shocked when the "dead" came back to life. What I liked best was the longer it went the worse the one that didn't curl up was able to cling to the sides or top. I caught them feeding under leaves and figure if they can't hold on they probably can't feed. I also didn't see any attempts to fly.
It took no time for them to curl up "dead", except the one. It was days for them to come out of it. I think they were dead in a week (and I put a leaf in there (that may have been sprayed) so they could eat).

I'll see if I can find a post about it.

I didn't think about letting it dry. That would be an interesting one to do if I ever catch some again. Maybe spray a leaf, let it dry and drop it in.

Pyganic is natural pyreththrum and not an affective PC killer. It's low residual activity makes it not very useful for fruit trees and even organic growers don't tend to use it in their programs as far as I know.

In the book "The Apple Grower" (Michael Phillips) he mentions a grower uses Surround initially and then when PC activity is very high it hits it all with Pyganic. Not sure how effective, he mentions Pyrethrum has a very short residual activity like you say, on the order of 4 hrs!

I see the local farm stores are selling a product called "Maxide":
Q: What is the active ingredient in Maxide Insect Killer?
A: Maxide Insect Killer combines the proven performance of lambda-cyhalothrin and thiamethoxam which offers effective knockdown and residual control of several turf damaging insects and nuisance pests.

I may just go with TRIAZICIDE.

Thanks Myk.

Now that you mention it, I think I remember your old post.

It's surprising the wet spray didn't kill the curcs immediately. But beetles tend to be pretty tough. I remember last year I tried to control curcs with Mustang Max (zeta-cypermethrin) and still got damage.

But I think you got pretty good control last year with Triazicide, didn't you?

Strange thing about PC and Triazicide for me. With nothing my Arkansas Black is nearly left alone and what egg laying attempts it gets usually go nowhere. My Cortland and McIntosh get wiped out.
With Triazicide my Cortland and McIntosh get very few drunk hits that go nowhere and they focus on the Arkansas Black.
They still seem to be too hard for many to be successful. Maybe that's the brain damage and they can't tell which is too hard.

They also left my cherries alone until I started spraying, so there must be some repellent effect.

I can't say how it does with the Lodi, since they're early I only get one spray on and bag everything ASAP.
The real test will come when my plums start bearing. They hit my last ones very early and very hard.

All in all, yes I'm very happy with the results I get with Triazicide since it is easy to get and works on PC. I would rather be able to get Imidan.