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The Impacts of Hot Days with Night Warming on Small Insect Pests

Paper Reviewed
Zhao, F., Zhang, W., Hoffmann, A.A. and Ma, C.-S. 2014. Night warming on hot days produces novel impacts on development, survival and reproduction in a small arthropod. Journal of Animal Ecology 83: 769-778.

According to Zhao et al. (2014), "under global climate change, the increase of mean temperature over land is characterized by diurnal asymmetric patterns with greater trends of night warming than day warming," as revealed by the work of Karl et al. (1993), Easterling et al. (1997) and Caesar et al. (2006). Yet they say that in spite of this fact, "night warming has not been considered much in modelling and predicting changes in populations of insects and other ectotherms."

In light of this common neglect, Zhao et al. decided to investigate the impact of changing night temperatures (NTs) on hot days by testing the combined effects of daytime heat stress and night warming on the life-history traits and population dynamics of the English grain aphid Silobion avenae, which they describe as "an important global cereal pest common in temperate climates," citing van Emden and Harrington (2007). This they did by creating six different temperature treatments: a common daytime temperature maximum (DTmax) associated with six different NTmin values that fell between 13 and 25°C, in order to separate the thermal effects of NTs on aphid fitness during hot days.

In describing their findings the four researchers report that night warming "reduced aphid survival under heat from 75% to 37% and depressed adult performance by up to 50%," so that "overall," as they write, "night warming exacerbated the detrimental effects of hot days on the intrinsic rate of population increase, which was predicted to drop by 30% when night-time minimum temperatures exceeded 20°C."

The take-home message of this work is that although many average or mean temperature models predict increasing pest outbreaks in a warming world, the results of Zhao et al. suggest that "outbreaks of some species might decrease due to the effects of night warming on population dynamics." But try getting a climate alarmist to admit that!

References
Caesar, J., Alexander, L. and Vose, R. 2006. Large-scale changes in observed daily maximum and minimum temperatures: creation and analysis of a new gridded data set. Journal of Geophysical Research 111: 10.1029/2005JD006280.

Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Karl, T.R., Jones, P.D., Knight, R.W., Kukla, G., Plummer, N., Razuvayev, V., Gallo, K.P., Lindseay, J., Charlson, R.J. and Peterson, T.C. 1993. A new perspective on recent global warming: Asymmetric trends of daily maximum and minimum temperature. Bulletin of the American Meteorological Society 74: 1007-1023.

van Emden, H. and Harrington, R. 2007. Aphids as Crop Pests. CABI, Wallingford, UK.

Posted 10 October 2014