The researchers focused on the Samoan islands of Upolu and Savaii, where in 2001, males of the Blue Moon butterfly made up only 1 percent of the population. In 2006, the researchers embarked on a new survey of the butterfly after an increase in reports of male-sightings at Upolu.
They found that males that year made up about 41 percent of the Blue Moon butterfly population in Upolu. They hatched eggs from 14 females in the lab and confirmed that the male offspring from this group were surviving with sex ratios near parity. For Savaii, the population was initially 99 percent female at the beginning of 2006. By the end of the year, researchers found that males made up 39 percent of the 54 butterflies collected.
The researchers tested for the continued presence of Wolbachia in the butterflies. By mating infected females with males from a different island that did not have the suppressor gene, they also confirmed that the bacteria were still effective at killing male embryos. The male-killing ability of the bacteria emerged again after three generations. Thus, they could rule out a change in the bacteria as an explanation for the resurgence of the males in the butterfly populations studied.