When searching on Scots pines, females of the aphid parasitoid Pauesia silvestris responded to differences in mortality risks, host distribution and host quality by changing foraging tactics. They foraged more successfully (i.e. they laid more eggs per unit time) on the pine aphid Cinara pini than on Cinara pineaTherefore, the former species was considered to be of higher quality. However, P. silvestris suffered from a high mortality (19.5%) from ant aggression when foraging for C. piniwhile mortality was zero on pines with C. pineaAll females that were killed were foraging on the bark, while females searching on needles were safe from ant attacks. When searching for C. pineaP. silvestris spent significantly more time on needles if the aphid colonies were ant-attended. On pines with C. piniin contrast, females spent more time on bark in ant-attended colonies. The high adult mortality risk on bark was counterbalanced by a significantly higher foraging success in ant-attended colonies.