This wasn’t actually found on our property, and properly speaking they don’t even live in the wild in Michigan, but if we keep bringing in houseplants we will probably get an infestation of them sooner or later. Our friend Michelle found it, along with a bunch of others, in a greenhouse at the University, and gave it to us so I could get some pictures.
It’s clearly a mealybug, family Pseudococcidae. They are a semi-tropical group and can’t survive outdoors in our rather harsh climate, but they are ideally suited to greenhouses, where they are a serious pest
They don’t have a lot of features, they basically look like a blob, with thin, thread-like legs. The legs are hard to see here, because the whole bug is only a couple of millimeters long, after all, but if you roll one over and look at the underside, they are there.
Those white projections on the back are not actually part of the bug, they are wax filaments. They secrete the wax partly to keep themselves from drying out, partly for camouflage, and partly to fend off predators. Supposedly, they are called mealybugs because the wax coating makes them look like they’ve been rolled in flour (which some people call “meal”)
This is a female, which is the type normally seen and that do most of the damage. There are male mealybugs, but you’ll hardly ever see them. They have wings, and look like a tiny gnat. The male mealybugs aren’t strictly necessary for reproduction, because the females can reproduce parthenogenically. But, the occasional male does let them mix up their genes from time to time in order to get the benefits of genetic diversity.
Depending on which mealybug species this is, it either lays a huge number of eggs, or gives birth to obscene numbers of live young. Michelle said that they reproduced fast and spread like crazy in the greenhouse, which kind of implies that the young ones are probably a lot more nimble and quick than the slow-moving, kind of clumsy adults. They were an ongoing problem that was very difficult to keep down. Not only do they cause direct damage themselves, they evidently also vector diseases between plants, so you really don’t want them around if you can help it.
As far as controlling them, there are apparently a lot of approaches that have varying degrees of success. Insecticides apparently don’t work as well as one might like, both because mealybugs tend to hide out under leaves and because the wax coating protects them from a lot of chemicals. Insecticidal soaps (which basically wet them down so that they can drown, and wash them off of the plant) sometimes help. Michelle says that the following procedure actually was one of the most effective things to do:
We used an alcohol swab method to kill them in the greenhouse. We
used 70% ethanol and dabbed all the critters and their eggs. That was really our most effective method. They were completely devastating to our trees, mostly because of the fungus they injected into the tree when feeding. We had to simultaneously treat with a systemic fungicide as well, but we still lost more than 50% of our trees at various times.
For small situations, like say houseplants, the easiest and cheapest thing to do is generally just to go over the plant every few days and squish them.
In cases where one has time, and assuming that you just need to keep the numbers down, there is a beetle known as the mealybug destroyer that is evidently an excellent predator of mealybugs. They were imported from Australia, and both the larvae and the adults eat mealybugs, along with similar things like aphids. The larvae of the mealybug destroyer actually look quite a lot like mealybugs themselves, complete with the wax filaments, although they get a bit bigger. They are popular in greenhouses, although there is one thing to keep in mind: you have a choice of using chemical control or biological control, but usually can’t use both. If you are spraying insecticides already, then the insecticides will also kill any mealybug destroyers that may be introduced. So, if you want to use them, you need to plan ahead.
 They used a lot of insecticides, which Michelle didn’t appreciate very much.