Background
The author writes that the Western flower thrip (Frankliniella occidentalis) "is one of the most important and difficult to control plant pests," as "it feeds on numerous plant species and spreads the tomato spotted wilt virus, which also affects numerous plant species."

What was done
Heagle grew well watered and fertilized white clover (Trifolium repens) plants from virus-free stolons in 1-liter pots filled with Metro Mix 220 that were placed between two rows of thrip-invested plants growing in 15-liter pots, after which they were grown for either 27 or 35 additional days in continuous-stirred tank reactor chambers (CSTRs) that were maintained at either ambient or elevated atmospheric CO2 concentrations (396 or 745 ppm) and located within a non-filtered-air greenhouse.

What was learned
The USDA researcher reports that "at elevated CO2, clover shoot weight and laminae weight were ˜50% greater, and laminar area was ˜20% greater than at ambient CO2." In addition, he notes that the "thrips population size was not significantly affected by CO2, but laminar area scarred by thrips feeding was ˜90% greater at elevated than at ambient CO2." Nevertheless, because of the CO2-induced increase in clover growth, "undamaged leaf area was approximately 15% greater at elevated than at ambient CO2."

What it means
Because there was a "net increase in undamaged leaf area" in the elevated CO2 treatment, as Heagle describes it, and because it occurred "despite feeding by a relatively high thrips population," we could conclude that the ongoing rise in the air's CO2 content will provide a net benefit to white clover plants, and possibly other plants as well. Because of the brevity of the experiment, however, as well as its being conducted in CSTRs located within a greenhouse, Heagle takes a more conservative stance -- and rightly so -- stating that "whether or not elevated CO2 will be a net benefit for T. repens under field conditions remains to be determined."