Comparison of two population‐level ecotoxicological endpoints: The intrinsic (rm) and instantaneous (ri) rates of increase

Abstract

AbstractThe instantaneous rate of increase (ri) was compared to the intrinsic rate of increase (rm) as an alternative population‐level ecotoxicological endpoint. The terrestrial arthropodAcyrthosiphon pisumHarris, the pea aphid, was used as the model species and the new nicotinergic insecticide, imidacloprid, as the xenobiotic. In the first experiment,rmwas generated each day from a life table forA. pisumneonates exposed to nontreated (control) potted broad bean,Vicia fabaL. (variety Banner), and compared to determine the earliestrmwhich was not significantly different from the finalrm. Thermfor neonates introduced to nontreated plants was significantly different on days 6 and 7 but not significantly different between 8 to 40 d postintroduction. A second experiment examined the change inriover time for neonates introduced at birth to nontreated broad bean and censused at 8, 11, 13, 15, 17, 19, and 21 d postintroduction. Therifor neonate populations introduced to nontreated broad bean peaked on days 11 and 19. Therion nontreated beans was significantly different (p< 0.05) fromrmon days 8 and 15 but not significantly different at 11, 13, 17, 19, and 21 d. A third experiment was conducted comparingrmandrifollowing 11 d exposure to a range of imidacloprid concentrations applied to broad bean. There was a high correlation (r= 0.91,n= 21,p< 0.01) betweenriandrm11 d after the start of the study, suggesting thatrican be used as a predictive measure in place ofrm. There was a negative relationship,y= 0.32 – 0.43x(r2= 0.88,n= 21), betweenriand exposure to imidacloprid‐treated broad bean, suggesting that simple regressions may be utilized as tools in the assessment of xenobiotics on population growth rates.