Vedalia beetle
The vedalia beetle is a lady beetle about 1/8 in (3 mm) long, red and black and finely hairy, that eats cottony cushion scale and almost nothing else. Imported from Australia in the winter of 1888–89, it saved California's young citrus industry within a year and became the textbook case of classical biological control. It is now classed as Novius cardinalis. You cannot buy it: UC IPM says no commercial insectary rears it. Where scale is a problem, look for its red eggs and larvae on the scale's egg sacs, stop spraying, and if none are there, move some in from another tree.
At a glance
- Kind
- Wild — not sold; move it, don't buy it
- Adult
- About 1/8 in (3 mm); red and black, hairy
- Larva
- Red when young, later dark pink to greyish; up to 1/4 in (6–7 mm)
- Eats
- Cottony cushion scale, every stage
- Egg to adult
- 4–6 weeks when warm
- Stalls
- Above 90 °F (32 °C) daily highs
How it works
By the 1880s cottony cushion scale, an Australian insect, was killing citrus trees across California's young orchards. Over the winter of 1888–89, 514 vedalia beetles were shipped from Australia. They multiplied so fast that by June 12, 1889, officials handed out 10,555 beetles to 208 growers. By the autumn of 1889 the scale was under control wherever the beetle had been released, for a project cost of about $1,500. The parasitic fly Cryptochaetum iceryae came from Australia at the same time. The pair still give complete control of the scale on most hosts in California, unless sprays disrupt them. The California beetles also founded populations in Egypt, Portugal, Chile, Hawaii and many other places.
The female lays red, oblong eggs under the scale or attached to its white egg sac. The young larvae chew into the sac and eat the eggs and crawlers, and older larvae and adults eat every stage. A female lays 150–190 eggs according to Cornell, or several hundred over a 1–3 month life according to UC IPM. The beetle breeds far faster than its prey, fitting four generations into one of the scale's: eight a year on the cool California coast and twelve inland. The weakness is heat. When daily highs pass 90 °F (32 °C), usually by June in the San Joaquin Valley, egg-laying stops and the larvae slow down, so the beetle does its work in spring. On the coast the fly does most of the work; in the Central Valley and the deserts, where summer heat and dry air hold the fly back, the beetle is the main control.
What it is confused with
The adult is easy to recognise once you know it. The young larva is the stage people mistake for the pest.
- PestCottony cushion scale crawlers — Scale crawlers have black legs and black antennae. A first-instar vedalia larva has red legs and no obvious antennae.
- Also goodMealybug destroyer (Cryptolaemus) — Also a small lady beetle on scale and mealybug colonies, but the adult is blackish with an orange-brown head and thorax, and its larva is covered in white wax.
- Also goodConvergent lady beetle — Larger, 4–7 mm, shiny orange with up to 13 black spots and white marks on the thorax. It mainly eats aphids and other soft-bodied insects.
- Also goodScale killed by Cryptochaetum — A scale with a neat round exit hole, or a yellow, orange, dark red or black fly puparium beside it, was killed by the parasitic fly, the beetle's partner on the coast.
How to keep it around
Vedalia finds cottony cushion scale on its own, and when the scale is gone it flies off to look for more. The job is to keep sprays from killing it, and to give it a start where it has not arrived.
- Look first: check the white egg sacs for red eggs and reddish larvae, and nearby leaves for pupal cases, before doing anything else
- If none have arrived by the end of March, collect adults, larvae or pupae from another infested tree and place them on scale in several trees. UC IPM says as few as 20 can found a population, in February to April
- Do not use imidacloprid. UC IPM says it does not kill cottony cushion scale but is very toxic to vedalia
- Avoid pyrethroids, neonicotinoids and insect growth regulators. UC IPM says these kill vedalia, and pyriproxyfen also stops its eggs hatching
- Control ants tending the scale, with sticky trunk bands or baits, because they drive off natural enemies
- Grow flowering plants nearby and hose dust off small plants; UC IPM recommends both to keep predators and parasitoids working
Pesticide sensitivity
UC IPM says pyrethroids, neonicotinoids and insect growth regulators such as buprofezin are toxic to vedalia, and rates malathion and carbaryl as harmful to most natural enemies. Cornell adds that the pyrethroid cyfluthrin (Baythroid) kills the beetles and stops egg-laying for about a month. In the DDT era, spraying wiped out the beetle in Central Valley citrus, and it took growers three years to change their spray programs and recolonise their orchards. Open the compatibility matrix →
When to choose something else
Vedalia is the answer to cottony cushion scale and almost nothing else. Look elsewhere when:
- The scale is not cottony cushion scale. For mealybugs use the mealybug destroyer; for armoured scale use Aphytis melinus
- It is midsummer in a hot inland garden and the beetle has stalled. In citrus, UC IPM times any spray for June–July, after vedalia has done its spring work, and horticultural oil is the least disruptive
- You want to buy something today. No insectary sells vedalia, and no trial of the mealybug destroyer against cottony cushion scale was found
Vedalia beetle by target
What it eats and when it turns up differ by pest. Each page below is the picture for one target.