Abstract

The modern outbreak of pasture mealybug causing "pasture dieback" in eastern Australia was long thought to be a new "variant" of Heliococcus summervillei Brookes (Hemiptera: Pseudococcidae). However, major, consistent morphological differences and distinct differences in the sequence data (8.6% COI difference, 1.6% difference in 28S D2/D3, and 1.3% difference in 18S) between the two variants support that these are two separate species. Herein, we describe Heliococcus novovillei Powell and Miller, new species, the new pasture mealybug that has caused major pasture dieback and "yellow canopy syndrome" in Australia for over a decade and, as of at least 2025, is causing major damage to pasture grass and sugarcane in the southern United States (Florida, Louisiana, Texas) and Mexico. Both H. summervillei and H. novovillei are present in Australia but, remarkably, both have now been detected in the United States (Florida and Texas). We posit that H. summervillei may have been introduced to the United States earlier and is not present at damaging levels. Instead, it is the far more abundant H. novovillei that is now at outbreak infestation levels in Australia and the United States. We provide the history of this taxonomic conundrum, descriptions, illustrations, images, sequence data, useful primers for rapid identification, and host data for both H. novovillei and H. summervillei.