INSECT HELPERS
At this time of year many gardeners are praising the benefits of tiny little helpers – ladybugs. These valuable insects are commonly used for controlling pests in the garden. In fact, they are the most popular and widely used beneficial insects for commercial and home use.
Ladybugs are capable of consuming 50-60 aphids per day but will also eat a variety of other insects and larvae including scales, mealy bugs, leaf hoppers, mites and various soft-bodied insects.
Unfortunately, the ladybugs cannot help us when it comes to invasive plants, but we do have a myriad of insects that work hard to help us in our battle to control these unwanted species.
We are fortunate in B.C., as our province has been a real leader in the utilization of biological control, or the use of natural enemies for the suppression of invasive plant populations.
The earliest release dates back to 1952 with the introduction of the St. John’s-wort defoliating beetle. Our province now has records for over 80 insect species that target 30 invasive plants.
Eighty per cent of these bioagents have been purposely introduced while the remainder have found their own way into B.C.
Prior to establishing a biological control agent, insects must be screened for host specificity to the target plant.
Seeds of native and agricultural plants in close association with the invasive species are collected and shipped to Switzerland where they are germinated and tested for damage from the potential agent. The agents are then tested to determine their impact to the host plant.
Depending on biology, bioagents will attack many different parts of a plant. Some reduce seed production in the larval stage by feeding on seed heads, and can also decrease plant strength by feeding on foliage during their adult stage.
Others directly weaken the plants by attacking the plant tissue or root reserves, resulting in stunted growth and reduced reproductive vigour.
In B.C.’s Southern Interior, biological control has been particularly successful. Many invasive plants are now considered under control in localized areas due to the establishment of biological control agents.
These species include diffuse knapweed, Dalmatian toadflax, purple loosestrife, St. John’s-wort and hound’s-tongue.
Many people are familiar with the knapweed insects, especially those that attack the root.
I have received many phone calls over the years from anxious landowners who have pulled knapweed plants only to discover grubs in the roots.
In fact, 12 bioagents have been released in B.C. for diffuse and spotted knapweed.
The seedhead weevil can be observed right now. It is a small grey-brown weevil that feeds on young knapweed leaves and flowers during the spring and summer, and their larvae consume the entire contents of the flower head in which they were laid.
The stem-mining weevil that feeds on Dalmatian toadflax is also a welcome and common sight in our region right now.
This invasive plant with its bright yellow snapdragon flowers was once prolific along our roadsides and grassland habitats.
However, the release of the weevil has seriously thwarted the spread of this invader. The female weevils chew holes into stems and oviposit a single egg into each. When larvae hatch, they mine the centre of the shoot and then pupate in the stem.
Stems generally swell and crack with the developing larvae inside, and the stem portion above the larvae often dies.
The new adults over winter in the stem and emerge in spring to start the whole process over again.
Landowners wondering if biological control is the right option for their property need to first determine their long-term goal.
If eradication of the invasive plant is the goal, then biological control should not be considered. Bioagents will only suppress infestations to a more environmentally and economically acceptable level.
Biological control is proving to be one of the most effective means of controlling invasive plant infestations that have reached significant proportions. Agents are selfpropagating and self-dispersing, thus supporting a long-term, costeffective and environmentally friendly means of control.
In areas with sensitive habitats and difficult access, biocontrol is even more important and often the only practical choice.
For information on invasive species go to our website: www.oasiss.ca or contact the Program Coordinator for the Okanagan-Similkameen, Lisa Scott, at 250-404-0115.