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Research Project:
Enhancing Yellow Starthistle Biological Control in the Field
Location:
Exotic and Invasive Weeds Research
Project Number: 5325-22000-018-03
Project Type:
Reimbursable
Start Date: Jan 01, 2002
End Date: Dec 31, 2004
Objective:
This project will test the hypothesis that adding nitrogen to yellow starthistle plants will increase population densities of insect biological control agents released in California ecosystems. If adding N to yellow starthistle plants enhances growth and reproduction of Chaetorellia succinea and Eutstenopus villosus, then by fertilizing small plots in a an infested area it may be possible to "jump start" or enhance the build-up of population densities to a level that would have a greater impact on yellow starthistle seed production than is currently observed.
Approach:
Insects (Chaetorellia succinea and Eutstenopus villosus) will be raised in 15 separate outdoor cages, each containing three yellow starthistle plants of known tissue N concentrations. Fifteen pairs (male, female) of insects will be allowed to oviposit on yellow starthistle flowers for one week. Cages will be removed to allow pollination of flowers. After which bags will be placed over the flowers, and flies allowed to emerge. Survivorship and adult size will be determined. A number of measurements of adult size including wing length, tibia length, head width, and dry weight will be made. At a site that has the biological control agents present, we will establish 100, 5 x 5-m plots. Various levels of nitrogen will be added as ammonium nitrate. In June, July, and September, each plot will be sampled for the abundance of biological control agents. Nitrogen content of the insects will be determined with a Perkin-Elmer model 2400 CHN analyzer. In addition, to determine if the plants in the nitrogen-amended plots are more attractive to ovipositing females, we will perform timed counts. The total number of flowers on plants in at least five randomly placed 10 x 10 cm quadrats will be counted. At the end of the growing season yellow starthistle flowers will be collected, dissected, and the presence of insect larvae noted. Insect larvae will be dried, weighed, and their nitrogen content determined. The number of seeds present in 25 damaged and undamaged flowers will also be determined. Documents Reimbursable with CDFA. Log 20418. Formerly 5325-22000-016-09R (10/03).
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