DNA testing has confirmed that the parasitoid wasp Ooencyrtus pitosina is indeed a species of its own, contributing to our understanding of the Samoan swallowtail butterfly and its relationships with other species. This knowledge is essential in preventing the extinction of the butterfly.
For almost 140 years, a previously undiscovered species of wasp, Ooencyrtus pitosina, has remained hidden in plain sight on the island of Tutuila in American Samoa. It was first noticed by naval officer and entomologist Gervase Frederick Mathew in 1885 when he observed tiny insects attacking the eggs of the Samoan swallowtail butterfly. Although the behavior was documented in a scientific journal, the wasp was never formally described until now. A team of researchers led by Dr. Andrew Polaszek from the Natural History Museum has identified and described the species, hoping to inspire further research on this little-known wasp. Dr. Polaszek states, “This may be a record for the time elapsed between species identification and formal description, demonstrating that describing a species is more complex than simply assigning a name.”
During the 1880s, identifying whether Ooencyrtus pitosina was a new species posed significant challenges. The butterfly host had only been officially described about two decades earlier, limiting knowledge about the butterfly itself, which hindered the exploration of the wasp. The findings of this study have been published in the journal PLOS One.
The Samoan islands, with their unique wildlife, cover an expanse of over 3,000 square kilometers in the Pacific Ocean. Being isolated, they are home to various species of animals and plants found nowhere else in the world, including the tooth-billed pigeon and Samoan starling. The Samoan swallowtail butterfly, also known as Papilio godeffroyi, is one of only three known species of this butterfly type in the Pacific region. While it was once abundant on the larger Samoan islands, it is now restricted to Tutuila and became extinct on the other islands in the late 1970s or early 1980s. The Samoan swallowtail now occupies just 5% of its former range.
The causes of the butterfly’s population decline are not fully understood, but it is suspected that human destruction of its forest habitat and tropical storms have contributed to the decline of the talafalu tree, which is crucial for the butterfly’s egg-laying. These trees are equally important to the parasitic wasp Ooencyrtus pitosina, which lays its eggs inside the butterfly’s eggs. The wasp larvae hatch and consume the butterfly eggs from within, eventually developing into adult wasps. Although it may initially appear that the wasps are contributing to the butterfly’s decline, Dr. Andrew argues that they play a crucial role. He explains, “While the wasp appears to be the villain by killing the butterfly, it actually helps maintain the balance of the ecosystem by controlling the butterfly population. Without the wasp, the swallowtail larvae could overwhelm the trees, depleting their food source and pushing themselves closer to extinction.”
Given their interdependent relationships, the survival of the three species on Tutuila is interconnected. With the Samoan swallowtail now classified as Endangered, the extinction of this butterfly would likely result in the extinction of Ooencyrtus pitosina as well. Co-author Dr. Mark Schmaedick emphasizes that while it is probable that Mathew’s observation of the egg parasitoid on P. godeffroyi in the Samoan islands and on the closely related Papilio schmeltzi in Fiji is indeed O. pitosina, it is currently challenging to verify. He notes, “We have yet to find evidence if it parasitizes other species besides the Samoan swallowtail or occurs outside its range. Although we have not yet detected its presence through typical general collecting methods, it is difficult to say.” The extinction of this wasp would result in more than just the loss of one species, as DNA sequencing suggests that it is not closely related to any other known wasp species.
Fortunately, any measures taken to benefit the Samoan swallowtail also assist the wasp. Proposals to reintroduce the butterfly from Tutuila to the neighboring islands of Samoa will need to consider the presence of the wasp, which could help stabilize its population. To ensure the success of the reintroduction, a deeper understanding of the Samoan swallowtail and Ooencyrtus pitosina is necessary. The researchers plan to continue their research next year with the goal of safeguarding the future of these interconnected species.
Citation: Pacific wasp named as a new species more than a century after first being spotted (2023, August 8) retrieved 8 August 2023 from https://phys.org/news/2023-08-pacific-wasp-species-century.html
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