Porgera, a gold mine in the highlands of Papua New Guinea, is not a pleasant place for a biologist, especially if you are aware of the massive environmental damage of its operations, or the frequent human right violations that this mining camp is known for. But we had no choice but to sleep with the enemy, and ask for the mine’s help in helicoptering us into the remote highlands of PNG where our team was surveying animals and plants. Luckily, the heavily guarded fortress of Porgera had one redeeming quality – at night I was allowed to wander around our sleeping quarters and look for insects. This, being New Guinea, guaranteed that even a place as dismal as a mining camp was bound to reward me with something interesting. And I was not disappointed – not only did I find a lot of insects, but one of them turned out to be new to science. (Yes, I am aware of the irony of a mining camp being the type locality and the site of the only known population of Pandangraecia porgera Naskrecki and Rentz, 2010.) But the insect that really stood out in the crowd was a katydid Phyllophora boschmai, a member of a remarkable lineage of my favorite insects.
The Phyllophorinae, known as the helmeted katydids (the names hooded katydids or box katydids are also used) are found primarily on New Guinea and nearby islands, although a handful of species venture into northeastern Australia, and a few places in the Philippines, Sri Lanka, and Taiwan. What immediately sets them apart is their size – many species are massive, and one, Siliquofera grandis, is the largest living katydid, with the wingspan of over 8 inches (20 cm)! Their morphology is also unusual – the pronotum, the part of the thorax immediately behind the head, is greatly expanded into a huge, helmet-like structure that covers the thorax and parts of the wings; in nymphs the pronotum may cover the entire body. This type of the pronotum usually indicates that the katydid is an exceptionally loud singer since the pronotum can act as a resonator and an amplifier of the call produced by the sound-producing apparatus at the base of the wings. But this is where things get interesting. If you were to peek under the huge pronotum of a helmeted katydid, you would find nothing. No sound-producing organs, no stridulatory file, nothing. These katydids cannot sing.
It appears that the huge pronotum is there solely as a defensive mechanism, protecting the softer, more vulnerable parts of the body. Why helmeted katydids have lost the ability to sing is still a mystery, especially considering the fact that they are a highly derived group, closely related to some of the loudest singers in the family, the Mecopodinae. But the real question is, how do males and females find each other?
In katydids, the acoustic communication – attracting each other with a song produced by rubbing their wings – is the only way (that we know of) for the two sexes to get together as these insects lack pheromonal communication or any other way to send long distance signals (some katydids use substrate vibrations to communicate, but this only works over short distances). But helmeted katydids are not entirely silent, either. They have evolved unique stridulatory structures at the base of their legs that allow them to produce loud, rustling noises, which both males and females use as a defense mechanism if they happen to be assaulted by a predator (click here to listen to the defensive stridulation of a helmeted katydid). These structures, however, cannot be used to attract the opposite sex in the dense vegetation of the New Guinea rainforest, and the mechanism by which the sexes locate each other is completely unknown.
But it wouldn’t be, if only I had the presence of mind to watch them more closely. While in Papua New Guinea I captured a male and a female of Phyllophora sp., and placed them in a large mesh cage. I kept looking at the pair, waiting for something to happen, but then it was dinner time and I was hungry and, long story short, when I came back the two were already relaxing with a cigarette in hand – I missed the whole thing! And it probably was quite a spectacle – I knew that they had successfully mated because the female now carried what looked like a pair of white testicles, a nuptial gift from the male. In many katydid species the male produces a similar gift, known as the spermatophylax, that the female later consumes. Why they do it is another story, but in an essence this is to prevent her from mating with another partner, and to ensure that the male’s sperm has time to enter her body. In this way the edible spermatophylax, which encapsulates a pair of small vesicles containing sperm, is indeed, from the functional point of view, a pair of autonomous testicles that the male attaches to the female.
And so the mechanism of the helmeted katydids’ long range communication remains a mystery. I never had a chance to watch these insects again, but hope to be able to return to New Guinea at some point, and finally document their courtship ritual, dinner be damned.
P.S. David Rentz, who also participated in the PNG katydid survey, has revised Australian Phyllophorinae, and wrote a post about these insects on his excellent blog BunyipCo.