Beneficial Insects


The Shasta County Department of Agriculture assists the State in the fight against noxious weeds by releasing insects that feed exclusively on those plants.

Efforts to control several target species are underway, including the following:

  • Diffuse, Spotted, and Squarrose Knapweed
  • Puncturevine
  • Purple Loosestrife
  • Yellow Star thistle

Some of our activities involve:

  • Collection and redistribution of established biological control agents
  • Education
  • Location of new release sites
  • Monitoring of effectiveness
  • Release of new biological control agents

Biocontrol Links

Biocontrol FAQs

How can I find out which types of insects are beneficial and which types are pests?

A great source for information concerning beneficial insects is the University of California Integrated Pest Management Program available online at You may also contact us at (530)224-4949.

I have a lot of Yellow Star thistle (YST) I would like to get rid of. I heard there was an insect that feeds on it. Where can I obtain these insects and how well will they work on my property?

The Yellow Star thistle Hairy Weevil  has established well in Shasta County. In fact, we now consider it "generally distributed". The insect's larvae feed on the developing seeds of YST and can result in a YST population decline over several years...when left undisturbed. The key to success is to prevent grazing, application of pesticides, or mowing. We find that most property owners are looking for a more rapid control solution. More information available for various YST control methods.