Location: Invasive Species and Pollinator Health
Project Number: 2030-22000-033-009-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jun 1, 2020
End Date: May 31, 2025
1. To increase the numbers of a newly permitted weed biological control agent of yellow starthistle, making greater numbers of the insect available for release in the field. a. Determine the period of time needed to complete diapause development. b. Improve methods to rear the weevil on potted yellow starthistle plants. c. Optimize an artificial diet to rear larvae. d. Optimize conditions to maintain diapausing adults to stockpile them for release. e. Train stakeholders to rear and release the weevil.
The weevil, Ceratapion basicorne, was recently approved for release as a new biological control agent of yellow starthistle (YST). This weevil normally has one generation per year, which greatly limits increasing the population for release. We currently have a small number of adults in our quarantine laboratory that were collected at Kilkis, Greece in May 2019. We put them in cold dark conditions early and will try to produce two generations this year using our current methods on potted YST plants. This will provide more adults available for experimentation, which involves 5 subobjectives. 1) Increasing the number of generations per year. We will test the period of time needed to complete diapause development under cold dark conditions to find the shortest period required. We will also measure the effect of temperature on fecundity of females during the egg-laying period to determine the optimum temperature, and minimize the oviposition period. 2) Improving methods to rear the weevil on potted yellow starthistle plants. This is currently labor intensive, but reliable. We will test the exposure period to optimize the number of eggs laid per female per plant that produce progeny, and study the effect of plant size and number of larvae per plant on larval survival. 3) Optimizing an artificial diet to rear larvae. We will start with the Tomic-Carruthers diet and use a multi-dimensional statistical approach to vary the proportions of the ingredients to optimize weevil survival and body size. This technique was successfully used to improve the effectiveness of a diet for the citrus root weevil (Diaprepes abbreviatus). 4) Optimizing conditions to maintain diapausing adults to stockpile them for release. Adults produced 'out of season' could be released directly in the field, but because this is abnormal, we would expect to see either low survival, or dispersal which would lower the chances of successful establishment. We think that it would be best to hold them under winter conditions for release in the early spring when they are ready to lay eggs. Thus, as we produce adults out of season, we will put them in winter conditions and test the effect of different conditions (temperature and humidity) on survivorship to maximize it. 5) Train others to mass rear the weevil. We will train others on current methods of rearing, which will empower them to start multiplying the insect in their own regions. Furthermore, having different teams rearing the insects is likely to foster innovations that will improve the methods. As the artificial diet and overwintering methods improve, we will also provide these methods to interested producers.