Genetic basis for host range expansion of a native moth, Eudryas unio Hubner, onto an introduced plant, Lythrum salicaria L.
Host range expansion by herbivorous insects has been of interest to agriculturalists and evolutionary biologists. Pests that adapt to new crops are of concern and importance. Similarly, comparative ecology of invasive and non-invasive species is of interest to ecologists. Studies on the genetic variation present in herbivores which allows them to incorporate new hosts provide data that have implications to our understanding of the speciation process. This study focused on the incorporation of an introduced European invasive plant, Lythrum salicaria, into the diet of the North American moth, Eudryas unio. Results of this study will have implications for population genetics and host-specificity theory of importance to practitioners of biological control of weeds.
Preliminary evidence suggested that populations of E. unio differ in their ability to utilize L. salicaria and their closely related traditional host, Decodon verticillatus. Quantitative genetic experiments were designed to identify divergent host-use patterns between E. unio populations from L. salicaria and from D. verticillatus. Amount of genetic variation was estimated for larval performance traits (development time and pupal weight) and adult oviposition preference for this moth on its two host plants. Genetic correlations were determined for performance traits and between preference and performance. This studies use of newly developed mixed model methodology and statistical analysis allowed for improved estimation of genetic variation and genetic correlations. High levels of additive genetic variation were indicated for both E. unio populations on the two host plants in both performance traits. Genetic correlations for pupal weight and development time between host plant species were generally significantly greater than zero. Thus, no negative trade-offs in performance were identified for this insect herbivore to expand its host range onto the novel host, L. salicaria. Significant genetic variation in oviposition preference was also identified for the two E. unio populations. No positive genetic correlations were detected between preference and either performance trait measured. However, a significant negative correlation was identified for the Lythrum-E. unio population between preference and pupal weight on D. verticillatus. Females from this population were placing a high proportion of eggs on a plant that was poorly suited for their offspring.