Recent host records for Gephyraulus raphanistri (Kieffer), a flower-gall midge, show restriction to Raphanus raphanistrum throughout Europe. Gephyraulus raphanistri has never been confirmed from commercially grown Brassica crops. Historical records showing a broad host range appear to have resulted from confusion with new or as yet undescribed Gephyraulus spp. and with Contarinia nasturtii (Kieffer), a known gall-former of Brassica and other related genera. This study tested field host specificity of G. raphanistri in Europe by manipulating host plant phenology of actual and potential hosts in the genera Raphanus and Brassica as part of a risk assessment of the insect as a potential biological control agent for R. raphanistrum, one of the most important weeds of crops in Australia. Raphanus raphanistrum raphanistrum (wild radish), R. raphanistrum landra (coastal wild radish), Raphanus sativus (radish) and Brassica napus (oilseed rape cultivar) were phenologically synchronised for initial flowering and planted out in a flowering time and species block design near a natural population of R. r. landra hosting a natural population of G. raphanistri. Three generation peaks in gall formation were visible in the experiment, with galls developing on all test plants with an apparent preference for R. r. landra. High field specificity in this gall midge is driven by synchrony of oviposition and flower availability and not host physiological incompatibility or behavioural unacceptability. Commercially grown Brassica spp. are not suitable hosts for G. raphanistri only because they have different flowering phenology in natural conditions compared to Raphanus raphanistrum. The overlap between flowering phenology of the crop and weed in Australia makes the insect unsuitable as a biological control agent.
|Number of pages||7|
|Journal||European Journal of Entomology|
|Publication status||Published - Jan 2008|