Performance of a generalist grasshopper on a C 3 and a C 4 grass: compensation for the effects of elevated CO 2 on plant nutritional quality

Abstract

The increasing CO2 concentration in Earth's atmosphere is expected to cause a greater decline in the nutritional quality of C3 than C4 plants. As a compensatory response, herbivorous insects may increase their feeding disproportionately on C3 plants. These hypotheses were tested by growing the grasses Lolium multiflorum C3) and Bouteloua curtipendula C4) at ambient (370 ppm) and elevated (740 ppm) CO2 levels in open top chambers in the field, and comparing the growth and digestive efficiencies of the generalist grasshopper Melanoplus sanguinipes on each of the four plant x CO2 treatment combinations. As expected, the nutritional quality of the C3 grass declined to a greater extent than did that of the C4 grass at elevated CO2; protein levels declined in the C3 grass, while levels of carbohydrates (sugar, fructan and starch) increased. However, M. sanguinipes did not significantly increase its consumption rate to compensate for the lower nutritional quality of the C3 grass grown under elevated CO2. Instead, these grasshoppers appear to use post-ingestive mechanisms to maintain their growth rates on the C3 grass under elevated CO2. Consumption rates of the C3 and C4 grasses were also similar, demonstrating a lack of compensatory feeding on the C4 grass. We also examined the relative efficiencies of nutrient utilization from a C3 and C4 grass by M. sanguinipes to test the basis for the C4 plant avoidance hypothesis. Contrary to this hypothesis, neither protein nor sugar was digested with a lower efficiency from the C4 grass than from the C3 grass. A novel finding of this study is that fructan, a potentially large carbohydrate source in C3 grasses, is utilized by grasshoppers. Based on the higher nutrient levels in the C3 grass and the better growth performance of M. sanguinipes on this grass at both CO2 levels, we conclude that C3 grasses are likely to remain better host plants than C4 grasses in future CO2 conditions.

Quantitative analysis of diet structure by real-time PCR, reveals different feeding patterns by two dominant grasshopper species

“…Studies of grasshoppers diet structure within plant communities are important for grasshopper control and protection of plant resources485556. Using real-time PCR.…”

Growth and reproduction of the alpine grasshopper Miramella alpina feeding on CO2-enriched dwarf shrubs at treeline

“…The importance of post-ingestive mechanisms was recently shown in a study with Melanoplus grasshoppers feeding on C 3 and C 4 grasses growing at ambient or elevated CO 2 (Barbehenn et al 2004). Although the nutritional quality of C 3 grasses declined to a greater extent than that of C 4 grasses in elevated CO 2 , no differences in grasshopper growth rates or consumption rates were found.…”

Effects of nitrogen fertilization on tritrophic interactions

“…Insect herbivores typically need to reach a certain size before molting to the next stage of development, and N availability will influence this process. Furthermore, the nutritional indices, such as approximate digestibility index (AD), efficiency of conversion of ingested food (ECI) and/or efficiency of conversion of assimilated or digested food (ECD) of insects feeding on low N food are typically decreased (Mattson 1980;Chen et al 2004; but see Barbehenn et al 2004). This means more low-N food is Effects of nitrogen fertilization on tritrophic interactions 83 needed by many insects to complete their development, which may be exacerbated by the general increase in induction of anti-feedants and toxins in lower N plants.…”

“…To compensate for low N availability in N-stressed plants, insects tend to adjust their total food consumption by increasing consumption rates, prolonging feeding periods, or a combination of the two, or by adjusting their nutrient processing efficiency, for example through changes in food residence time or digestive enzyme levels (Mattson 1980;Barbehenn et al 2004). Paper birch, Betula papyrifera (Betulaceae), grown under elevated CO 2 environments had decreased N content (Lindroth et al 1995).…”