The California Red Scale

CRSpageThe California Red Scale is not technically a major pest in eastern North American forests, but it is worth describing here for several reasons.  1) We have been battling it for a long time, and have failed to eradicate it, which is a lesson.  2) It is a representative of a ubiquitous group of pests that affect many trees and have similar traits (the scale insects).  3) It has one of the most interesting biocontrol stories, which is often touted as a “success” story although the scale insect is still a major pest.  4) Conventional control methods (i.e. pesticides) fail to work on this insect because it has a waxy protective coating that makes chemicals ineffective.

Scale insects belong to the same order as the Woolly Adelgid, and have the same piercing, sucking mouthparts.  They feed on the plant in the same way, and  have a similar protective wax.  However, unlike the Woolly Adelgid, this wax takes the form of a smooth scale (you may have seen these reddish scales on your citrus fruits before, now you know that they are actually insects!).

One of the most interesting things about the scale insects is their life history.  The female never looks like a real insect…even as an adult, it is a kidney shaped blob, and it always stays beneath its protective scale.  A single female can produce between 100-150 offspring, which are called crawlers as they crawl out from underneath her scale over a period of days.

The males, however, do look like insects…in fact, they look a lot like their close cousins, the aphids.  This allows them to fly around looking for females to fertilize.

The biocontrol story of the Red Scale is an interesting one…it is often touted as a success story.  The ladybird beetle (or ladybug, if you absolutely must *sigh*) is a major predator of the scale insects, but there have also been some introduced parasitoid wasps.

These introduced predators can indeed control the populations of the aphids, and they are the preferred method.  However, control is the important word…biocontrol predators have never eradicated a pest species.  Something to ponder!


3 thoughts on “The California Red Scale

  1. Pingback: San Jose Scale Insect | standingoutinmyfield

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