The Cochineal insect is difficult to get rid of once an invasion begins. Opuntias and Chollas are its favorite meal. The first step to try to rid the cactus of the insect is to spray it with a strong spray of water to dislodge the waxy coating, causing the insect to die when exposed. In this photo, you can see the small holes left by the insects, as well as the insect itself. Those dark dots in the center of the white stuff are exposed insects. If that doesn't work, and in the case of my cactus, it didn't--spraying with an Isopropyl alcohol/water mixture is the next step. I've done that and it didn't help this cactus, so the next step will a soap spray.
The final step is usually a chemical application. I don't want to use Malathion because I have a Jade Plant very close to the Prickly Pear, and Jades are very susceptible to Malathion. Even a little bit of stray spray can kill them. However Malathion doesn't seem to bother Prickly Pear at all.
If I can't get this under control soon, I'm going to have to take out this cactus, which is now close to five feet high, in order to keep it from spreading to my other Opuntias. The last best hope is that a a swarm of common predators, such as Lady Bugs, will swoop in and promptly devour the Cochineal insects, but Lady Bugs are few and far between around here. Even if I bought some to use, they usually just take off, and you just can't herd Lady Bugs.
This is the test to determine if the invasion is truly the Cochineal insect. Cochineal means 'scarlet colored', and when squished, the insect is filled with the dark red substance. It's almost like a tick when full--except much smaller. The female is only about a quarter inch long. The red substance was used for centuries as a dye, and in some regions of the world, it still is. There are even Prickly Pear/Cochineal farms in regions of Mexico, Algeria and the Canary Islands.
The Cochineal insect is also used a natural food coloring in place of aniline dye. It's probably best to keep that under wraps. Many folks would be appalled to know their favorite red-colored food may contain the contents of an insect belly!