Impact of elevated CO2 on insect herbivore –host interactions.

Abstract

An alternative procedure to deal with the limitations of the qualitative synthesis of studies was put forward and came to be known as ‘meta analysis’. The quantification of impact of elevated carbon dioxide (eCO2 ) on the incidence of insect pests through statistical synthesis of published results or meta-analysis is attempted here. Integration of findings of independent studies by calculating the magnitude of treatment effects i.e., “effect size” is estimated. Data for the meta analysis were gathered from the published studies (88 articles) in selected journals (28) for comparing the growth and development of insect herbivores under eCO2 conditions and compared with ambient CO2 condition. The basic requirements of the each study were identified as follows The following criteria were identified for each study: (1) Studies pertaining to elevated CO2 levels. (2) Studies reporting information on the mean of the parameters along with a measures of variance (standard error, standard deviation , coefficient of variance and confidence intervals). (3) Studies that reported the design of experimentation and sample size for all the treatments. The mean effect sizes for various insect parameters varied significantly. Among the insect primary parameters consumption (2.94) and duration of insect species (0.751) were found to be significantly positive under eCO2 and other parameters like weight (-0.46) and population abundance (-0.05) of species were negative. Insect performance indices showed positive effect size for approximate digestibility, AD (1.281) and relative consumption rate, RCR (3.61) and negative with respect to efficiency of conversion of ingested food, ECI (-3.20), efficiency of conversion of digested food, ECD (-1.891) and relative growth rate, RGR (-1.072). Meta analysis of biochemical constituents of host plants indicated that the effect sizes were found to be negative (Nitrogen) and positive (Carbon and C: N ratio) indicating a significant variation of constituents under eCO2 condition than ambient CO2 condition. The implications and limitations of meta analysis were discussed.