Pyriform scale
Pyriform scale (Protopulvinaria pyriformis) , also known as heart-shaped scale, is an exotic plant pest that threatens Australia’s forests, horticulture, and gardens.
Background
The pest has a wide host range, affecting more than 100 species across 34 plant families. It was first discovered in Perth’s metropolitan area in 2015, and later spread to a variety of plants in surrounding suburbs.
Pyriform scale can travel long distances as people transport host material, particularly nursery stock and ornamental plants. These insects can move onto nearby plants via wind.
There are restrictions on brining host plants in South Australia, per the Plant Quarantine Standard (PQS). This applies to all nursery stock, other than bare-rooted plants without leaves, and cut flowers.
Impacts
Pyriform scale could devastate our avocado, citrus, mango, banana, and passionfruit, forestry, and garden industries.
It causes direct damage by feeding on plant sap from the underside of leaves, stopping their nutrient uptake. Heavy infestations of pyriform scale can:
- affect plant vitality
- cause leaf drop
- reduce the size and quality of fruit.
The insects secrete a clear, sugary honeydew which can cause sooty mould to develop on the leaves. This can spread to the fruit making it unsuitable for market, and it blocks the sunlight available to the plant.
Identification
Scale insects have a protective coating that gives them a raised, scab-like appearance on leaves. Adults are light brown with white fringing and can grow to 3 mm long.
First stage nymphs are transparent green in colour and their body later changes to light green.
Pyriform scales are not easily seen on the underside of leaves, but their honeydew secretion noticeably attracts ants.
Lifecycle
Female pyriform scale can reproduce asexually, laying up to 300 eggs without having to mate.
Nymphs emerge from eggs laid under the female’s body and crawl over the leaf to settle. Once they start feeding 1 to 2 days later, pyriform scale movement is minimal. They go through 3 growth stages before reaching adulthood.
