Cryptolaemus montrouzieri

White cottony fluff in the leaf axils and where the stems meet the pot, sticky leaves underneath, maybe black sooty mould on top — mealybugs. Cryptolaemus montrouzieri, the mealybug destroyer, is the specialist ladybird that eats almost nothing else, and it is the best answer there is to a mealybug colony. The reason it works where sprays do not is simple: a mealybug's wax repels water and it sits in crevices a spray cannot reach. A predator walks in.

It also asks nothing of you. Nothing to mix, nothing to spray, no residue on the leaves and no re-entry interval — you put them on the infested plant and leave them to it. They get into the leaf axils, the stem joints and the underside of the pot rim where you would need a cotton bud and an afternoon, they keep working long after a spray has dried, and mealybugs cannot develop resistance to being eaten. Safe around people, pets and anything you plan to eat.

Two stages, sold separately, doing different jobs. Larvae cannot fly. They stay on the plant you put them on until the colony is gone, which makes them the right buy for one or two badly infested plants. Adults fly, so they find scattered pockets across a collection and lay eggs for a generation behind them — but they will also leave if there is not enough to eat.

Which brings up the thing to be honest about before you buy. This beetle wants a colony, not a few insects. On a plant with three mealybugs on it the adults disperse looking for better, and the larvae have nothing to work with either. If your infestation is light, hand-wiping and a follow-up is the cheaper answer. Buy this when the mealybugs are clearly visible and in numbers.

Best for: A visible, established mealybug colony. 64–90°F, warm and humid — they are tropical in origin and slow right down in a cool room.
How many: 2–5 larvae or 2–5 adults per infested plant. Sizes go by plant count, with a separate count for each stage.
Arrives as: Adults loose with no carrier at all, or larvae in buckwheat hulls — the white waxy things in there are the predators and not an infestation, so resist the urge to squash them. Deploy the day they arrive; neither stage holds well in a container.
First, deal with the ants. They farm mealybugs for the honeydew and will kill your predators, and the larva's mimicry only gets it so far. Bait or barrier them two to three days before you release.
Long-tailed mealybug: They will eat it, but they cannot breed on it — long-tailed bears live young and leaves no egg sac for them to lay in. Expect repeat releases there rather than a generation of their own.
Safe around: People, pets, plants and food crops.
Not for: Armoured scale, the hard little limpets that will not squash — that is Rhyzobius lophanthae. Not root mealybugs either: this is a foliage hunter, and Stratiolaelaps scimitus or Sf nematodes are what reach the root zone. And a light infestation is genuinely the wrong job for it.

Where your larvae go

The mealybugs on your leaves are not the colony. They are the ones that left it, out feeding where you can see them. The colony itself sits somewhere sheltered — a leaf axil, the underside of a crown, the crevice where a stem meets the pot — and that is where the eggs and the wax are. That is where your larvae will head.

So the honest answer to "where are my larvae" is usually "wherever the main colony is." If you do not know where that is yet, finding it is the most useful hour you can spend on this plant.

Two things make them hard to spot even when you are standing over them. They look almost exactly like the pest they are eating — the poke test in the FAQs on this page is how you separate the two. And they are working the part of the plant you do not routinely look at.

Wipe off the ones you can see — once you have checked they are mealybugs and not your own larvae. The visible mealybugs are the minority, removing them by hand costs you nothing, and your larvae are not working that population anyway.

A larva that did not make it is obvious — it looks like a dead insect, not like nothing. Seeing nothing at all is the normal case.

Reading the first couple of weeks

Judge it on mealybug pressure, not on predator sightings. Around the two-week mark you will be looking at one of three pictures, and they mean different things.

• Pressure thinning. You have enough larvae for this colony. Leave them to finish.

• Pressure holding steady. The larvae are keeping up but not gaining. Release again — you are short, not wrong.

• Pressure quiet for a while, then climbing again. The larvae did the work and have since pupated. A larva has one feeding window: it eats through four increasingly large instars and then it stops. Release again.

Controlling an established mealybug colony usually takes weeks and more than one release. That is the shape of the method, not a sign it has gone wrong.