Opuntia dillenii (Ker Gawler) is an invasive plant species in Bundala National Park. The outstanding success of the cochineal insect, Dactylopius spp. in bio-control of the prickly pear, Opuntia spp. has been investigated worldwide. The present study reports the emergence of D. opuntiae as a pest of O. dillenii after several decades of its introduction to Sri Lanka. The intensity of infestation was 100% along three of the five transects surveyed and the overall damage was more than 50%. This recent outbreak of D. opuntiae may have resulted from an unnoticed existing population of D. opuntiae in the vicinity.