Cottony cushion scale

📖Overview

Icerya purchasi is a large scale insect in the family Monophlebidae. Females are slow-moving and usually found attached to plant stems, leaves or fruit where they feed on phloem sap. Females produce a distinctive cottony ovisac that can be 5-20 mm long and easily noticed. The species is a major pest in orchards and gardens because heavy infestations weaken plants, reduce fruit yield and produce honeydew that leads to sooty mold. Effective biological control by the vedalia beetle (Rodolia cardinalis) has historically reduced its impact in many regions.

🔍How to identify a cottony cushion scale

Adult females are roughly 4-6 mm long (body only), broadly oval and yellowish to reddish-brown beneath a dense white, cottony wax covering. The most obvious feature is the white, oval to elongate cottony ovisac or 'cushion' attached to the posterior; the ovisac may extend well beyond the body and reach 5-20 mm. Nymphs (crawlers) are tiny, mobile and pale before developing waxy filaments. Most individuals are self-fertilising hermaphrodites; males are rare, small, winged and short-lived.

1. Look for a conspicuous white, fluted cottony egg sac (ovisac) on stems, leaf axils or fruit.
2. Adults are roughly 4-6 mm long beneath the cottony covering; the body is yellowish-brown to reddish-brown.
3. Sticky honeydew and black sooty mold on leaves and fruit commonly indicate an infestation.
4. Inspect close to branch unions and leaf axils where ovisacs are often tucked in.

Lookalikes

↻Life cycle

1. 🥚

   Egg

   Females deposit eggs inside the cottony ovisac; eggs hatch after days to weeks depending on temperature.

2. 🐞

   Nymph (crawler)

   First-instar 'crawlers' are the main dispersal stage, spreading to new feeding sites on leaves and twigs where they insert their mouthparts.

3. 🐞

   Later nymphal instars

   Later nymphal instars feed mainly along leaf veins and twigs, develop a waxy covering and can still move short distances, typically migrating to larger branches as they mature.

4. 🐞

   Adult

   Adults are wingless, slow-moving and largely stationary once they begin producing the cottony ovisac. Most are self-fertilising hermaphrodites; males are rare.

🍃Diet and predators

🌱Effect on plants and gardens

Feeds on the phloem of many woody plants, especially citrus, oleander, bougainvillea, pittosporum and other ornamentals. Heavy infestations cause yellowing, leaf drop, reduced vigor and fruit damage; honeydew encourages sooty mold which reduces photosynthesis and marketability of fruit.

How to get rid of cottony cushion scales

For small infestations: physically remove ovisacs and egg masses with a brush or cloth, prune heavily infested branches and wash plants with a strong jet of water. Horticultural oils or insecticidal soaps applied thoroughly to cover the insects and ovisacs can be effective (follow label rates). For larger infestations or orchards: biological control using predatory lady beetles such as Rodolia cardinalis (vedalia) and parasitoid wasps has a proven record of long-term control. Systemic insecticides (e.g. some neonicotinoids) or targeted contact insecticides can be used where necessary, but consider nonchemical options first and follow local regulations and integrated pest management practices.

📍Where and when to find it

Check branch unions, leaf axils, undersides of leaves and fruit on citrus and many ornamentals. Look for white ovisacs, sticky honeydew and sooty mold. Crawlers may be found moving on leaves during warm weather.

✨Fun facts

• The cottony cushion scale was famously controlled in California citrus by introducing the vedalia beetle in the late 1800s, one of the earliest and most successful examples of classical biological control.
• Their conspicuous cottony ovisac is a protective structure for eggs and newly hatched crawlers.
• Ants often 'farm' these scales for honeydew and will aggressively defend them from predators.

?Frequently asked questions

📷Photos of the cottony cushion scale