To the naked eye, the blossoms of the orchid Oberonia japonica are so minuscule that they barely resemble traditional flowers. Instead, they take on the appearance of diminutive orange disks with a central white dot, swirling around a curved stem. Yuta Sunakawa, a graduate student at the University of Tokyo, highlighted the challenge of counting the petals of these flowers due to their size, stating that while it’s feasible to count the flowers, discerning the petals proves impossible. Each flower, measuring a mere two millimeters in width, is akin to the tip of a new crayon. This minute size is characteristic of all orchids within the Oberonia genus, commonly known as fairy orchids. Daniel Geiger, the malacology curator at the Santa Barbara Museum of Natural History, described these orchids as being both literally and figuratively overlooked.
The majority of flowering plants on Earth rely on pollination for reproduction, a process in which an animal transports pollen from one flower to another. Orchids have developed intricate adaptations to attract specific pollinators, increasing the likelihood of pollen transfer between flowers of the same species. For instance, the flower of the orchid resembles a female bee, enticing male bees to unknowingly spread pollen while attempting to mate with the flower. Charles Darwin, in his observations of the star-shaped orchid Angraecum sesquipedale with its remarkably long nectar tubes, hypothesized the existence of an insect with an elongated proboscis capable of reaching the nectar deep within the flower. Despite facing criticism for this theory, Darwin’s idea was validated in 1903 with the discovery of a sphinx moth species equipped with a suitable proboscis.
Over 130 years later, Sunakawa remarked on the persistent gaps in understanding orchid pollination. The identity of the pollinators responsible for over 90 percent of orchid species remains elusive. With approximately 28,000 orchid species, many of which are rare or inhabit challenging environments like epiphytic orchids found high in tree canopies, the task of studying them presents unique obstacles. Fairy orchids, due to their minute size, require microscopic examination to observe the pollinarium, the pollen mass crucial for insect-mediated pollination.
In the spring of 2022, Sunakawa serendipitously encountered an O. japonica orchid in a plum orchard before its bloom. Intrigued by the unidentified pollinator, he revisited the site in May with the landowner’s permission. Armed with determination, Sunakawa meticulously observed the orchids, eventually witnessing a gall midge trapped in one of the tiny flowers with pollinaria affixed to its head. Despite the absence of other midges initially, a swarm of flies appeared around the flowers late in the evening. Throughout the night, Sunakawa diligently monitored the flowers, capturing insects on camera and using an aspirator to collect them for further study. By the following morning, he had inspected over a thousand flowers and collected more than a hundred midges, all while fueled by his unwavering enthusiasm. These observations, detailing the pollination process, were recently published in a scientific journal.
The collection of 128 female gall midges, one-third of which bore pollen hats, provided compelling evidence of effective orchid pollination by these insects. However, the researchers are still puzzled by the benefits the midges derive from this relationship. While the orchid flowers may offer sugar, oil, or protein rewards, their diminutive size presents challenges in nectar collection. Another hypothesis posits that the orchid flowers mimic male gall midges or emit enticing floral scents to attract pollinators.
When discussing pollinators, bees and butterflies often come to mind, yet a myriad of species, including bats, skinks, slugs, and various insects like wasps, flies, and gnats, contribute significantly to pollination. Geiger emphasized the scarcity of knowledge regarding pollination in small-flowered orchids, contrasting with the extensive research on orchid bees, butterflies, and moths. He speculated on the potential role of ultraviolet visual cues in attracting pollinators to Oberonia, but his findings suggested otherwise, pointing to alternative sensory cues that appeal to small insects like gnats. The confirmation of midge pollinators through field observations marks a significant advancement in understanding pollination in small-flowered orchids.
Gall midges, a diminutive fly family often measuring less than three millimeters, exhibit fascinating reproductive behaviors, including pedogenesis, a form of asexual reproduction. Despite their enigmatic nature, gall midges play a vital role in pollination, with the potential to pollinate numerous small orchid species. While inconspicuous to human observers, these minuscule insects are precisely suited to fulfill the essential pollination tasks required by orchids.