I did it with the used grounds from Starbucks. They gave me some in a plastic transparent bag, I have no idea how much is there. Anyways, I've rebrewed them and already used the resulted liquid. It was pretty concentrated, imo. Now let's keep fingers crossed.

I have about 30 seedlings and a few bigger cycads and about 10 seedlings and less than 10 plumerias. I gave them all although only the cycad seedlings were attacked by the mealybugs, just to make sure no one of them is going to take refuge onto one of the unaffected plants.

Thank you all for the advice!

You did fine then. I've always felt weird about putting those old grounds in a coffee maker I would use for regular coffee, but I guess they are sterile enough.
This is the first time I heard this was for cycads. I'm happy to hear that the article was more helpful than I was thinking. So what kind of cycads do you have that got mealy bugs?

I have been tossing the spent coffee grounds, filter and all, under my cycads and have noticed scale is all but gone. If I find some, usually just a tiny few specks, I just remove that frond. It has worked so well I have started using them on a camellia that gets scale. I have about 2 dozen camellias and strangely (and fortunately) only one has been plagued. Once again the coffee grounds are doing the job. Spreading spent coffee grounds on the soil surface of container plants in the house seems to have eliminated the fungus gnat issue. I am a convert.

Edited to add - years ago I worked at a large commercial greenhouse and one day I had to call an ambulance because the owner had been spraying Orthene and next thing I knew he was unconscious. He had inhaled the spray and it almost killed him.

Orthene is a great pesticide but has a pretty obnoxious odor. I did not know the powder was lethal though. I would never use it in the house, just because of the odor.

So nice to see all the alternatives on this thread....I just posted about Imidacloprid in a different thread...it is linked to honey bee collapse and is just an awful chemical. If it's your last resort, don't use it. Throw the infested plant away or let nature take its course.

I'm trying the coffee grounds as mulch around plants that are prone to mealys and scale, but I have to wonder if those alkaloids Would also harm the bees and hummingbirds that feed on the nectar. It may be "organic", but it is still systemic, and the bugs still feed on the plant until it kills them. I'm thinking using it as a spray would be safer, though not nearly as convenient. Has anybody studied this?

From my years of testing, even before I wrote my article 7 years ago, I found that the larger insects in general were not affected by the coffee. Some insects are repelled by the coffee material. As an example, I poured the coffee material ask over some ants and that just swam around in it. Even after keeping them for a few days, they were still alive. Doing the same thing with grasshoppers and they were fine. It seems as if it over loafs the nervous system of smaller insects and doesn't seem to harm larger insects. This means that use of the coffee IS limited, but luckily, almost all the insects I have to desk with is taken care of by the coffee. My one problem with my hit pepper plants is pumpkin bugs, which eat hills in my peppers. Still going the manual method with these.