Tritrophic Investigation of the Evolution of Host Plant Use in an Insect Herbivore: A Case Study with a Leafminer (Amauromyza Flavifrons).

Abstract

Herbivorous insects are characterized by a great diversity of host-plant associations, yet the processes driving host range evolution are not fully understood. In my dissertation, I investigated ecological factors influencing the host plant use in an introduced leafmining fly, Amauromyza flavifrons, from tritrophic perspectives. Amauromyza flavifrons has two host plants, Silene latifolia and Saponaria officinalis in the study locality. When given a choice female flies prefer to oviposit on Si. latifolia over Sa. officinalis. Consistent with the preference-performance hypothesis, larval survival was greater on Si. latifolia than on Sa. officinalis in the absence of natural enemies, indicating that Si. latifolia is a higher quality host for larval development. Parasitism was also lower in Si. latifolia than Sa. officinalis patches, supporting the enemy-free space (EFS) hypothesis. Ephemeral patches of Si. latifolia provided A. flavifrons with EFS probably because parasitoid populations could not accumulate, since A. flavifrons population crashes in the middle of the summer. Parasitism was not random, but selectively removed leafminers with prolonged larval development period. Thus, parasitism is likely to play a significant role in shaping the evolution of life history traits, as well as oviposition preference of A. flavifrons. Despite higher mortality on Sa. officinalis, the density of A. flavifrons in the field was higher in Sa. officinalis than Si. latifolia patches. Sa. officinalis formed denser and seasonally more stable patches than Si. latifolia, suggesting that females searching for oviposition sites may locate Sa. officinalis patches more easily than Si. latifolia patches. Amauromyza flavifrons population as a whole continues to use both Si. latifolia and Sa. officinalis because specialization on either host may be less adaptive. I hypothesized that, although Si. latifolia is a better host for larval survival, females frequently accept Sa. officinalis due to its ease of host location. The pattern of host plant use in A. flavifrons is, therefore, shaped by overall trade-offs in fitness functions driven by multiple ecological forces.