Submitted to: Government Publication/Report
Publication Type: Government publication
Publication Acceptance Date: 6/10/2008
Publication Date: 6/30/2008
Citation: Smith, L. 2008. Genetic and behavioral discrimination of host plant populations of the leafbeetle, Psylliodes chalcomera, for biological control of yellow starthistle. Government Publication/Report. 12 p. Interpretive Summary: Yellow starthistle is an important alien weed that has invaded over 20 million acres in the western U.S. It is spiny plant that interferes with grazing livestock and outdoors recreation, it is fatally poisonous to horses, it outcompetes desirable vegetation, and reduces biodiversity. Although several insect biological control agents have become widely established, they attack only the flowerhead of the plant. Additional agents that attack the immature plant are needed. A genetically distinct Russian population of the flea beetle, Psylliodes chalcomera is being proposed for biological control of yellow starthistle. However, it is critical to develop methods to distinguish individuals of this population from those of other genetically distinct, but morphologically similar populations that attack other plant species, to ensure that we release only individuals that are specific to the target weed. We are developing both behavioral and non-lethal genetic assays to identify individuals before they are released for biological control of yellow starthistle. It is likely that these methods will enable others to discover and use cryptic species for biological control of other weeds.
Technical Abstract: Molecular genetic techniques clearly distinguish three separate populations within the flea beetle "species" Psylliodes chalcomera that are associated with three different host plants (yellow starthistle, Scotch thistle and musk thistle). Preliminary studies have not revealed any reliable morphological characters to distinguish adults of these populations. Experiments were initiated to develop an olfactometer capable of measuring preferences of an insect biological control agent to host plant odors. A three-way choice bioassay proved to be more reliable than an olfactometer to distinguish the three populations of P. chalcomera. We also refined a method to extract DNA from insect frass (feces) that enables us to identify live individuals without harming them. These advances provide reliable methods to discriminate live individuals, which are necessary to ensure the accuracy of host specificity evaluations and to be sure that the correct individuals are used for possible future releases as biological control agents of these invasive alien weeds.