Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2010
Publication Date: October 8, 2010
Citation: Logarzo, G.A., Casalinuovo, M.A., Piccinali, R., Braun, K. 2010. Geographic host use variabiliy and host range evolutionary dynamics in the phytophagous insect Apagomerella versicolor (Cerambycidae). Oecologia. 165:387-402.
Interpretive Summary: A longhorn beetle from Argentina was selected as a candidate for biological control of cocklebur in the United States. During the specificity studies in the field, the insect showed a geographical variation in host plant utilization, being monophagous in the north and polyphagous in the south of its distribution. The beetle was discarded as biological control agent because of its ample host range, however it is an excellent case study of a recent host expansion, an evolutionary process that is of short duration and difficult to find in nature. To investigate the mechanisms involved in host expansion of this insect we combined field studies on host plant availability and host use along a wide latitudinal range with laboratory studies on oviposition preference, mating success, diapause and mitochondrial DNA of the different insect geographical populations. We reconstructed the insect host history and concluded that the insect is in a host expansion and diversification process triggered by ecological factors, like weather and host plant availability. Insects host range has been thought as stable in time and space, at least in ecological time frames. However, recent host expansion cases like the present show that insects host range is dynamic and can exhibit spatial and temporal variation, a fact that has to be considered when evaluating host specificity of biological control agents.
The high diversity of phytophagous insects has been explained by the tendency of the group towards specialization; however, generalism may be advantageous in some environments. The cerambycid Apagomerella versicolor exhibits intraspecific geographical variation in host use. In northern Argentina it is highly specialized on the herb Pluchea sagittalis (Asteraceae), while in central and southern areas it uses seven Asteraceae species. To study host species geographical variation from ecological and evolutionary perspectives, we investigated field host availability and use across a wide latitudinal range, and performed laboratory studies on insect oviposition preference and larval performance and mitochondrial DNA (mtDNA) variation in a phylogeographical framework. Geographic variation in host use was unrelated to host availability but was highly associated with laboratory oviposition preference, larval performance, and mtDNA variation Genetic studies revealed three geographic races of A. versicolor with gene flow restriction and recent geographic expansion. Trophic generalism and oligophagy within A. versicolor seem to have evolved as adaptations to seasonal and spatial unavailability of the preferred host P. sagittalis in cooler areas of the species’ geographic range. No single genotype is successful in all environments; specialization may be advantageous in environments with uniform temporal and spatial host availability while being a trophic generalist may provide an adaptive advantage in host-constrained environments.