Abstract-The establishment of cause-effect relationships is fundamental for the interpretation and the predictive value of biomarker responses measured at all levels of biological complexity. In the present study, the biochemical exposure biomarker acetylcholinesterase (AChE) inhibition was related to locomotor behavior, representing a general effect biomarker at the organismal level. Both sexes of the carabid beetle Pterostichus cupreus were intoxicated with three doses of the organophosphorous insecticide dimethoate. Five elements of their locomotor behavior were measured for 4 h employing computer-aided video tracking, whereupon the whole body AChE activity was measured in the individual beetle. AChE inhibition was strongly correlated with dimethoate dose in both sexes. Alterations in the locomotor behavior were directly correlated with AChE inhibition in male beetles, which responded by reducing the time in locomotion, average velocity, and path length and by increasing the turning rate and frequency of stops. Females responded similarly at the two highest doses, whereas their locomotor behavior was not significantly different from the control group at the lowest dimethoate dose, suggesting a sex-dependent difference in behavioral sensitivity to minor AChE depressions. The results demonstrate that automated measurements of locomotor behavior is at least as sensitive an endpoint to organophosphate poisoning as the AChE assay. Further, the correlation between the molecular and behavioral responses in individual beetles indicates a mechanistic relationship between the two biomarkers.

The establishment of cause–effect relationships is fundamental for the interpretation and the predictive value of biomarker responses measured at all levels of biological complexity. In the present study, the biochemical exposure biomarker acetylcholin‐esterase (AChE) inhibition was related to locomotor behavior, representing a general effect biomarker at the organismal level. Both sexes of the carabid beetle Pterostichus cupreus were intoxicated with three doses of the organophosphorous insecticide dimethoate. Five elements of their locomotor behavior were measured for 4 h employing computer‐aided video tracking, whereupon the whole body AChE activity was measured in the individual beetle. AChE inhibition was strongly correlated with dimethoate dose in both sexes. Alterations in the locomotor behavior were directly correlated with AChE inhibition in male beetles, which responded by reducing the time in locomotion, average velocity, and path length and by increasing the turning rate and frequency of stops. Females responded similarly at the two highest doses, whereas their locomotor behavior was not significantly different from the control group at the lowest dimethoate dose, suggesting a sex‐dependent difference in behavioral sensitivity to minor AChE depressions. The results demonstrate that automated measurements of locomotor behavior is at least as sensitive an endpoint to organophosphate poisoning as the AChE assay. Further, the correlation between the molecular and behavioral responses in individual beetles indicates a mechanistic relationship between the two biomarkers.