Ann Paradis M.S. July 2003, co-advised with S. Louda Currently a PhD student at: University of Massachusetts, Amherst   Email: annieparadis@yahoo.com

Molecular assessment of the host association of a biological control agent Rhinocyllus conicus

Protocols used to evaluate potential insect biological control agents involve experiments designed to test the diet breadth of the insect, its oviposition preference, and larval preference and performance. These methods alone have proven insufficient in the case of the flowerhead weevil Rhinocyllus conicus. R. conicus was introduced to the U.S. in 1969 from its native European range in order to control musk thistle (Carduus nutans), a serious weed found in range lands. Overwintered adults emerge in early spring to mate and oviposit on the undersides of flowerheads. Larvae burrow into the flowerhead and feed on receptacle tissue and seeds, emerging as adults 6-9 weeks later and leaving the remaining seeds inviable.

In 1993, the weevil was discovered on Platte thistle (PL: Cirsium canescens), a native North American species found only in prairies in the Great Plains on sandy soils. Since that time it has been decreasing the population density of this thistle in Nebraska. Many other native thistles in the Midwest, California, and Canada support the complete development of R. conicus, yet presently no data exist to determine if their population densities are affected. Currently, the insect continues to be redistributed across the country. Two possible hypotheses explaining the observed host range expansion are:

1. the host preference and overall performance of the weevil have sufficiently changed since its introduction allowing it to develop on novel hosts, or
2. despite the stronger preference for Carduus species discovered during the initial screening process, R. conicus is capable of having an impact on native thistle species.

The objectives of my research are:
1) Determine the extent of genetic variation present in R. conicus, and if genetic sub-structuring exists.
2) Determine whether there is an association between haplotype of the weevil and host plant. In other words, are only certain haplotypes responsible for non-target feeding?