Establishment, Collection, and Redistribution of Bio-Control Insects

The minimum number of insects needed to establish a sustainable population is 200 insects, but more is generally better. The knapweed infestation for insect release and establishment should be at least two acres in area and moderately dense to very dense (three or more knapweed plants per square yard). Bio-control releases should only be made on land that will not be treated with herbicides in the following three to five years, and where relatively slow evidence of control will be acceptable. Sites should be open and not forested. Insects collected for redistribution should be released on the new site as soon as possible after they are collected, and kept cool (but not frozen) during collection, transport and storage. Retain collected insects in large coolers equipped with “blue ice” wrapped in towels so that direct contact is not made with the insect containers. Collected insects should be kept in breathable containers that allow air flow and where condensation will not form. Non-waxed ice cream containers work well, paper bags will work if they are not crushed or saturated when chilled, and pillow cases are convenient for collecting and transport. Do not use plastic bags. Including some fresh knapweed in the container reduces crowding and confinement stress, and gives the insects something to congregate and feed on.

Release sites may be marked with a steel post to help relocate the site for monitoring. Make sure you take the time to complete a release record for each release site; the record should include: date of release, species and number of insects released, site GPS coordinates or township/ range/section, and descriptive directions to the release point. Whole plant bouquets can be tied directly to the post or to fence posts. Weevils, moths and flies should be released on the ground within three feet of the marking post. The best time to release insects is during the cool times of the day in the morning or evening. Dump insects out of containers – this avoids attracting the attention of predators and curious wildlife or livestock, and prevents accidental drowning in the event of a significant rainfall! The post can be used as a photo point to sequentially monitor any change in the weed population and plant community after release.

It may take two to three years for an insect population to establish. High release numbers may reduce the time between establishment and significant impact.

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Last Modified: 06/02/2008