Reference
Reddy, G.V.P., Tossavainen, P., Nerg, A.-M. and Holopainen, J.K. 2004. Elevated atmospheric CO2 affects the chemical quality of Brassica plants and the growth rate of the specialist, Plutella xylostella, but not the generalist, Spodoptera littoralis. Journal of Agricultural and Food Chemistry 52: 4185-4191.
What was done
In the words of the authors, "cabbage, Brassica oleracea subsp. capitata (cv. Lennon and Rinda), and oilseed rape, Brassica rapa subsp. oleifera (cv. Valo and Tuli), plants were grown under ambient CO2 (360 ppm) or elevated CO2 (720 ppm) at 23/18°C and under a photoperiod of 22/2 hours light (250 ėmol m-2 s-1)/dark regime for up to 5 weeks," after which "the performance of the crucifer specialist Plutella xylostella (Lepidoptera: Plutellidae) and the generalist Spodoptera littoralis (Lepidoptera: Noctuidae) [that were allowed to feed] on those plants was studied."
What was learned
Reddy et al. report that "the mean RGR [relative growth rate] of P. xylostella larvae feeding on the CO2-enriched Lennos cultivar of cabbage declined 60% as compared to ambient (P < 0.05), while that of larvae feeding on the elevated CO2-grown Rinda cultivar declined only 43% (P < 0.05)." In addition, they report that "the RGR of the generalist S. littoralis showed a declining trend on CO2-grown cabbage leaves as compared to ambient (18% decrease with Lennon and 25% with Rinda), but these changes were not statistically significant."
When fed the other host plant (oilseed rape), Reddy et al. state that P. xylostella actually lost weight, producing negative RGR values that were significantly lower than the RGR values of larvae feeding on leaves grown in the ambient CO2 treatment (P < 0.001 for the Valo cultivar, P = 0.004 for the Tuli cultivar). They also report that RGR values of S. littoralis feeding on oilseed rape leaves grown in elevated CO2 "were only slightly lower than those measured for larvae feeding on leaves grown in ambient CO2 levels: 9% lower in Valo and 17% lower in Tuli," although these differences were also not statistically significant.
What it means
Because P. xylostella -- the "diamondback moth" -- is described by Reddy et al. as "one of the most serious pests of cruciferous plants throughout the world," as per the review of Talekar and Shelton (1993), these findings would appear to be welcome news indeed in a world where the air's CO2 content is on a sustained upward trajectory.
Reference
Talekar, N.S. and Shelton, A.M. 1993. Biology, ecology and management of diamondback moth. Annual Reviews of Entomology 38: 275-301.
Reviewed 15 September 2004