Paper Reviewed
Xu, H., Xie, H., Wu, S., Wang, Z. and He, K. 2019. Effects of elevated CO2 and increased N fertilization on plant secondary metabolites and chewing insect fitness. Frontiers in Plant Science 10: 739, doi: 10.3389/fpls.2019.00739.

There remains much to be learned about plant-insect interactions and how they might be impacted in the future by rising levels of atmospheric CO2. However, climate alarmists are quick to claim that the increased growth and biomass of plants due to CO2 enrichment will be met with even greater plant loss due to increased insect consumption, hypothesizing that insects will consume more plant tissue in order to obtain sufficient nitrogen in response to the sometimes-observed decline in plant tissue nitrogen concentration under elevated CO2.

But is this claim correct?

Xu et al. (2019) provide an answer with respect to maize and the Asian corn borer (Ostrinia furnacalis), which insect pest is responsible to 10-30% yield losses annually throughout China. In doing so, the five Chinese scientists conducted an experiment to investigate combined the effects of elevated CO2 and increased nitrogen (N) fertilization on maize-O. furnacalis interactions. The experiment was performed in controlled-environment chambers; the CO2 treatment included ambient (380 ppm) or elevated (750 ppm) and the N treatment included low (100 mg N/kg soil mixture), medium (200 mg N/kg soil mixture) or high (300 mg N/kg soil mixture).

Results of the study indicated the following: (1) "both elevated CO2 and increased N fertilization increased starch content, while increased N fertilization promoted the N content in maize," (2) the combined effects of elevated CO2 and N fertilization "did not influence the total non-structural carbohydrates:N ratio in maize," (3) the total phenolics content and defensive enzyme activities of maize increased under elevated CO2, increased N fertilization and O. furnacalis infestation." Additionally, the authors report that "relative to ambient CO2, elevated CO2 extended the duration of the [4] larval and [5] pupal stage by 3.99 and 7.13%, respectively; [6] reduced larval body mass by 5.64%; and decreased [7] mean relative growth rate, [8] efficiency of conversion of ingested food and [9] efficiency of conversion of digested diet by 4.15, 18.89 and 19.23%, respectively."

Consequently, the results of this study demonstrate that the resistance-related secondary metabolites in maize were enhanced by elevated CO2 and increased N fertilization (with or without O. furnacalis being present), which increased the plant's overall defensive response to combat O. furnacalis. Furthermore, elevated CO2 slowed the growth of the Asian corn borer and decreased its food digestibility and utilization. Consequently, in the Conclusion section of their paper, Xu et al. write that as the air's CO2 concentration rises in the years and decades ahead, farmers who utilize N fertilization in the production of maize will promote its resistance to the Asian corn borer. And that will translate to greater yields to be consumed by an ever-increasing planetary population.