A 114-year-old mystery in the leaf insect world has now been solved

Whereas we thought we were looking at two different species, now the Insectarium team discovers that the specimens belong to one and the same species.

Taxonomy, the science whose aim it is to organize and describe species on Earth, can be complicated, but even more so for people who work on cryptic species. They’re called cryptic because they’re difficult to find, thanks to their perfectly adapted camouflage. Here at the Insectarium de Montréal, Stéphane Le Tirant has devoted himself for four years to his favorite bug: leaf insects, or Phylliidae. These masters of camouflage from Southeast Asia and Australasia are large insects ‒ 25 to 110 millimeters long ‒ that look like leaves, with their flattened green bodies that flutter in the breeze.

FROM LEFT TO RIGHT - Entomology technicians at the Insectarium
Dominic Ouellette
Jennifer De Almeida, Thomas Théry, Mario Bonneau and
Thierry Boislard
Credit: Space for Life (Jennifer De Almeida)

In just the last four years, Stéphane Le Tirant, also curator of the scientific collection, and Royce Cumming, research fellow at the Insectarium, supported by Insectarium staff and management, have described 20 new species! This work has clarified a mystery going back 114 years and that would have been impossible without the contribution of the technicians and the rearing laboratory. Current technicians are Mario Bonneau, Thierry Boislard, Jennifer De Almeida, Dominic Ouellette and Thomas Théry, along with René Limoges, a technician who takes care of photographs and mounting of specimens for scientific publications.

Opposite sexes difficult to identify

The most recent work of “Team Phyllies” (the name of the team of Phylliidae researchers from around the world) has focused on revision of the Nanophyllium genus. Nanophyllium means “small leaf,” and that’s appropriate, because the leaf insects belonging to this genus are only 27 to 45 millimeters long. Their small size is nevertheless not the group’s most interesting aspect: the genus was described in 1906 based on a single male specimen by the renowned Austrian entomologist Josef Redtenbacher. Over the 111 years that have gone by since, only six other species have been named, each of them represented exclusively by males.

So where are the females of this genus? The problem of a missing opposite sex here is a consequence of the prominent sexual dimorphism of leaf insects. The term means that a male in no way resembles the female, even though they’re the same species. Generally, these problems of “missing sex” don’t last long in taxonomy, because observations in nature of breeding pairs immediately helps match up the unknown lovers. And besides, in the modern era of genetics, a simple DNA comparison can easily match the sex with another one’s. As a result, even though numerous species on Earth are sexually dimorphic, opposite sexes in a single species rarely remain unknown for very long. As it happens, though, in the case of leaf insects their camouflage is so faultless that it’s almost impossible to observe these creatures in nature. Moreover, the females are incapable of flight and live high up in the forest canopy, so they’re most often found and collected when a storm dislodges them from trees. Unhappily, the scarcity of this group means that all Nanophyllium species are rarely found in collections, and some are so old that they can’t be used in DNA studies to match with unknown females.

Luck-bearing eggs!

However, the year 2018 brought a stroke of good fortune when Stéphane Le Tirant received some eggs from another rare type of leaf insect, Phyllium (Pulchriphyllium) asekiense, a species from Morobe Province in Papua New Guinea. This one can display a variety of leaf colors ‒ green, yellow, brown and red ‒ and belongs to another interesting group of species called the frondosum group. As luck would have it, the only known specimens in this group were female.

Researchers in the past reflected on this puzzle, and the celebrated stick and leaf insect entomologist Paul Brock at the Natural History Museum in London (and also a founding member of the Insectarium) was the first to suggest that what could be involved was the opposite sex in the same group of species. This was in 2003. Unfortunately, at the time only two species of Nanophyllium were known, and Brock had no tangible proof to support his hypothesis.

In consequence, when the technicians from the Insectarium de Montréal’s insect rearing laboratory announced that they’d succeeded in raising three Phyllium asekiense individuals to adulthood, “Team Phyllies” was ecstatic. Not only was this species beautiful and rare, but two of these three individuals were clearly Nanophyllium males. Finally we have solid proof that the Nanophyllium genus (exclusively known from males) and the Phyllium frondosum group (exclusively known from females) were simply opposite sexes in the same group.

These results were recently published by members of the team in the international taxonomy journal ZooKeys after several months of work and studying collections from museums around the world with the goal of locating as many relevant specimens as possible for an examination of this group. Two new species, therefore, were described, after more than a century of being treated like different genuses. These species are now united within the same Nanophyllium genus thanks to the Insectarium de Montréal technicians’ team of experts, its curator, Stéphane Le Tirant, and Team Phyllies, which Royce Cumming serves as leader.