THE USE OF VARIANCE IN ENZYME-ACTIVITY AS AN INDICATOR OF LONG-TERM EXPOSURE TO TOXICANT-STRESSED ENVIRONMENTS IN CULEX-PIPIENS MOSQUITOS

1, The identification of easy to use and cheap biomarkers is important as a means of determining whether animals are developing under stress ful environmental conditions. Previous studies have indicated that the variance about the mean esterase activity in toxic environments incre ases in the absence of a significant shift in the mean value, suggesti ng that variance levels may have potential as a biomarker of toxicant- stressed or otherwise stressful environments. 2. Several field and lab oratory populations of the mosquito, Culex pipiens, were examined for esterase activities using a colorimetric assay and levels of polymorph ism using polyacrylamide gel electrophoresis. Some of these population s had been exposed to environmental toxicants (organophosphorus (OP) i nsecticides). 3. The OF-stressed field population had lower levels of polymorphism as indicated by fewer electromorphs than the populations that had not been exposed to OPs. However, the mean level of esterase activity was higher in the OF-stressed populations. 4. Despite having lower genetic variation, the OF-stressed populations showed much highe r levels of variation about the mean enzyme activity, at least two ord ers of magnitude higher, than the unstressed populations. Knowledge of the genetics of OF resistance in these populations confirmed that the increase in variance was not due to the general switching on of genes in response to stress. 5. One field population that had been exposed to heavy metal pollution had similar levels of esterase activity and v ariation about the mean as the unstressed populations, suggesting that variation only increases in characters directly affected by the envir onmental pollutant. 6. The probable factors causing the increase in va riance and the potential of this type of variation as a biomarker of s tressful environments are discussed.