Restored Prairie Response to Reduction in Ectophagous Insects

Author

Sarah Black, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2018

Degree Name

Master of Science

Department

Plant Biology

First Advisor

Baer, Sara

Abstract

Tallgrass prairie restorations generally aim to reconstruct native plant assemblages altered by disturbance to a composition of species characteristic of undegraded communities the region. Most prairie restorations, however, lack large herbivores such as Bison bison and Cervus canadensis, therefore leaving herbivory to Odocoileus virginanus, other small mammals, and insects. Although insects are more abundant by comparison, it is hypothesized that their influence as ecological drivers is often obscured by fire, grazing, and climate. Previous study in remnant prairie has shown that insects eat very little of above net primary productivity (ANPP), however they can alter the forb:grass ratio in prairies. Nonetheless, studies have shown that younger plants (particularly forbs) are more susceptible to insect herbivory due to higher nitrogen (N) content and physical and chemical defenses not yet fully developed. This research used an experimental approach (insecticide application) to reducing insect abundance and ectophagy to determine whether insects preferentially feed on forbs, alter forb:grass ratios, and affect diversity and aboveground net primary productivity (ANPP) in young (1-2 y) and more established (7-8 y) restored prairies. Ectophagy measurements showed that forbs were preferred over C4 grasses. Reduced herbivory decreased diversity of forbs and sown grasses, decreased percent cover of forbs, and species richness of sown grasses, and increased evenness in the youngest prairie. Contrary to expectations, ANPP and forb:grass ratios were not affected by treatment. Nevertheless, interactions between year and restoration age were often significant, suggesting that climate variability between seasons and maturity of community may influence how insect herbivores affect restored prairie. There was a positive correlation between herbivore morphospecies richness and sown forb richness. Insect communities were also characterized in restored prairies to evaluate treatment success. Insects were collected by sweep-netting. I collected 10 orders, 83 families, and 150 morphospecies. The largest number of species present was from Hemiptera (suborder Auchenorrhyncha). Species richness decreased through time. Pesticide application reduced diversity of families. Ectophagous insect abundance and richness were impacted by treatment, but piercing-sucking herbivores (Hemiptera) did not respond to insect reduction treatment. Predator/parasitoid insects were also reduced by treatment, indicating a larger sensitivity at higher trophic levels. Like plant diversity, interactions between restoration age and year affected almost all insect variables, suggesting that insect populations are dynamic and sensitive to nearby land-use.