Predator Interference with the Cinnabar Moth (Tyria jacobaeae) for the Biological Control of Tansy Ragwort (Senecio jacobaea)

Quantification of interference with biological control agents can provide support for anecdotal claims of success or failure of agent establishment and efficacy. This study was initiated because of observed predation of cinnabar moth larvae by carpenter ants when releasing larvae for the control of tansy ragwort, an invasive plant in Montana. Biotic and abiotic factors were compared among three sites with historically variable moth population establishment. Two experiments were developed to (1) observe and document insect activity, predation, or disappearance on tansy ragwort stems either protected or accessible to ants; and (2) quantify the effects of ant exclusion on herbivory of tansy ragwort. Site comparisons indicated that ant colony density was highest at the driest of three sites, and, interestingly, no ant colonies were detected at the site with higher observed numbers of moth larvae and adults and lower densities of tansy ragwort. Available substrate (logs and stumps) for ant colonization did not differ between the three sites. In the ant exclusion experiments, a larger number of larvae were missing on plants accessible to ants (63%) compared with plants where ants were excluded (39%) after 36 h. Direct observation of predation of larvae by carpenter ants accounted for 9% of missing larvae on stems accessible to ants. Larvae were able to consume 81% of original flowers or buds on ant-excluded stems, compared with 18% consumption on ant-accessible stems, suggesting that ant predation could limit the efficacy of cinnabar moth larvae. These results provide one of many possible explanations for the anecdotal observations of large, persistent populations of cinnabar moths in moist areas. This work emphasizes the importance of post-release observation and monitoring to detect and, ideally, quantify factors to support anecdotal perceptions regarding the fate and subsequent efficacy of insect biological-control agents.

Molecular analysis of a consortium of ruminal microbes that detoxify pyrrolizidine alkaloids

Members of a consortium of bacteria, isolated from the rumen of sheep, that degrades pyrrolizidine alkaloids (PAs) found in tansy ragwort (Senecio jacobaea) were characterized. An enrichment of ruminal bacteria was isolated from a sample of ruminal fluid using standard anaerobic techniques. The PA degradative capacity of the enrichment was tested by spiking purified PA extract from tansy ragwort. Length heterogeneity analysis by PCR (LH-PCR) and restriction fragment length polymorphism (RFLP) analysis was used to identify members of the consortium. Phylogenetic analysis of the 16S rDNA gene revealed differing results based on the molecular method used. LH-PCR identified 7 different organisms in 3 groups while RFLP identified 6 organisms with differing banding patterns in 5 groups. After the phylogenetic analyses of both methods were combined, the combined isolates represented 6 groups. The majority of the members of this consortium are <97.0% homologous with known bacteria, indicating this consortium may contain novel organisms able to detoxify PAs found in tansy ragwort. Further understanding of the metabolic pathways used by this consortium to degrade PAs could lead to the use of the consortium as a probiotic therapy for livestock and horses afflicted with tansy ragwort toxicosis.Key words: pyrrolizidine alkaloids, ruminal bacteria, tansy ragwort, RFLP, LH-PCR.