Meta analysis of Impact of elevated CO2 on host - insect herbivore interactions

Abstract

The possible impacts of elevated CO2 (eCO2 ) on growth and development behavior of insect pests attracted the attention of researchers. Several reviews of such studies were attempted to draw conclusions on the impact of elevated CO2 on insect pest incidence. These reviews were mainly qualitative summaries of the studies and the conclusions drawn are not based on any statistical or quantitative analysis. These reviews were subjective and often based on votecounting method. They did not consider the magnitude of the impact and sample size observed in the individual studies and in the process the valuable information available in the original studies is lost. When studies reporting differential impact are included in the review, it becomes that much more difficult to draw conclusion on the overall impact of the treatment under question. Hence, the validity of these conclusions remains questionable. It is only possible to draw some generalizations, which have little statistical validity, and it is also not possible to quantify the magnitude of the effect of treatment. Most of the reviews (Coviella and Trumble, 1999; Hunter, 2001; and Srinivasa Rao et al 2006) attempted to examine the impact of elevated CO2 on insect pest incidence also suffer from the above mentioned limitations. The summary of qualitative literature survey on the impact of elevated CO2 on insect pests was documented by earlier reviewers. From such exercises, only subjective generalizations can be drawn rather than any quantified effect of interest, which has some statistical validity. An alternative procedure to deal with the limitations of the qualitative synthesis of studies was put forward initially by Glass (1976) and came to be known as meta analysis. Quantification of effect of eCO2 on the incidence of insect pests through statistical synthesis of published results or meta analysis is attempted here. The purpose of this bulletin is to synthesize the information on the elevated CO2 – insect pest population relationships and to draw statistically valid conclusions using meta analysis as a tool.