Friday, 1 September 2017

Cottony Cushion Scale Destroyers - Rodolia Cardinalis

Top: Rodolia cardinalis adults attacking cottony cushion scale.
Photo: J.K. Clark, University of California Statewide IPM Project
You will most probably have seen cottony cushion scale Icerya purchasi which look like little bundles of fluff that sticks to your plants in their hundreds. They are an Australian native soft-bodied scale insect which breed quickly and will cover all parts of the plant and they suck sap from plants. However it's not the sucking that's the problem, it's the amount of honeydew they produce. Lots of honeydew brings lots of sooty mould, a black coating that can cover the entire plant. This black coating prevents the plant from photosynthesizing, resulting in leaf drop, twig death and general stress of the plant.

The cottony cushion scale were responsible for the first, very successful biological control measure in California where they had practically wiped out the second largest industry, citrus. Albert Koebele, a German born entomologist travelled to Australia to investigate what held the cottony cushion scale in check. He captured hundreds of Rodolia cardinalis and returned to California where he placed the beetles on an infested orange tree enclosed in a tent. In a few months, the beetles had multiplied prolifically and had devoured the scale insects. When the tent was opened, the beetles spread throughout adjoining trees and soon the entire orchard was free of the cottony cushion scale. The beetles spread rapidly and by 1890 the California citrus industry was practically free of the pest.

The adult female ladybird lay their eggs underneath the scale egg sac where it's a smorgasbord of 'all you can eat' and they do!

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