Monday, May 18, 2015

Rhubarb Weevil

Rhubarb weevils (Lixus concavus) also known as Rhubarb Curculios are commonly found throughout the Eastern United States and portions of the Western United States such as Utah, Idaho and Texas. There are known populations in Ontario, Canada as well. 

They use plants in the genus Rheum as their host plant, much to the detriment of their offspring (more on this below). This includes Rhubarb, from whence this beetle gets it's common name. But they also use other plants including dock, thistle and sunflower. I find them frequently in May on curly dock that grows near our garden. In March and April when the curly dock is young and tender it attracts a completely different beetle called a Green Dock Beetle. When those beetles leave, the weevils show up and feed on the dock in its much larger state. 

Adult beetles overwinter in leaf litter and become active in May. They will begin laying eggs in host plants, typically one egg per plant. Even though these beetles share a common name with the rhubarb plant, they cannot complete their life cycle within the stalks of rhubarb. Eggs laid within the stalks of rhubarb are quickly consumed by a sticky sap-like substance that the plant produces in response to a foreign object or injury. This destroys the egg(s). Instead the weevil will use sunflower, thistle and dock most often as a suitable host. About 10 days after the eggs are laid the larvae will hatch and begin feeding. They work their way down the stalk to the ground where they will pupate. This process takes approximately 9 weeks. Right before pupating the larvae will chew an exit hole into the plant that the adult can emerge from after completing pupation. The adults will feed for a few weeks on the leaves of the plants before the colder temperatures drive them into sheltered areas where they will spend the winter. 

This species of weevil is one of the largest in North America, reaching up to 1/2 inch in length. They are black beetles covered in a fine golden dust. Like many beetles when they are alarmed they will roll over and play dead often rolling off the leaf or plant that they are feeding on. This must work well for the beetle, as I've had them do this and they virtually disappear once they hit the ground never to be seen again. 

If you have these beetles feeding on your sunflowers or rhubarb, usually handpicking the beetles and destroying them is sufficient to get rid of them as they rarely show up in large numbers. It is also recommended to kill plants like dock or thistle, which may be nearby your garden plants, that are also used as host plants. This can go a long way in reducing their numbers. Make sure to kill the plants in June when the larvae will be inside the plant feeding. Since we do not grow sunflowers or rhubarb I don't worry about them at all. The curly dock they feed on here is a pest plant and they are welcome to it. Plus I find them attractive and interesting beetles.



  1. Unusual to eat the leaves, I thought they were lethal. I have a few photos to share with you. I had sparrows hit a bluebird house and when I took out the nest I should have bagged it just to look over all the detrivores eating in there. Always thinking of you, LOL

  2. I fight sparrows all the time. They take over my martin houses and my bluebirds houses here as well. They are the bane of bird life. I love that detrivores brings me to mind.....LOL Can't wait to see your photos. I always enjoy seeing what you find.