Guwahati: Researchers from Ashoka University and Punjab University have discovered three new bush cricket species namely Hexacentrus khasiensis in Meghalaya and Hexacentrus ashoka and Hexacentrus tiddae in Haryana’s Sonepat district.
Hexacentrus ashoka and Hexacentrus tiddae have been found in and around the Ashoka University campus in Sonepat.
The researchers are Aarini Ghosh, Ranjana Jaiswara, Monaal, Shagun Sabharwal, Vivek Dasoju, Anubhab Bhattacharjee, and Bittu Kaveri Rajaraman.
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“All the 3 species from Hexacentrus genera can produce ultrasonic sounds up to 60 kHz. Our ears can only hear up to 20 kHz. But they can hear ultrasonic sounds. Their calling song sounds like an unusual mechanical buzz. All three species have a unique camouflage in terms of their colour and leaf-like shape, which helps them hunt other insects and with protection from a predator,” Aarini Ghosh a Ph.D. biology student at Ashoka University told EastMojo.
Bush crickets belong to an order called Orthoptera. This order includes species of grasshoppers and crickets. Out of this, crickets are divided into two groups- true crickets (ground and tree crickets) and bush crickets/katydids. Crickets are nocturnal in nature.
“Crickets and bush crickets (also known as katydids) produce sounds via modified forewings. One wing has a row of teeth in a file and the other wing has a scraper, which the scraper is rubbed against the teeth to generate sounds that are amplified by the vibration of the wing. These crickets have a pair of tympana (thin membranes) in each forelimb to receive sounds, similar to the human eardrum,” said Dr. Bittu Kaveri Rajaraman of the Biology department at Ashoka University.
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Hexacentrus are largely found on bushes, from lower to middle vertical strata. They inhabit a variety of habitats, from deciduous forests to thorny scrub areas to dense sub-tropical forests. Male specimens were collected by focally locating the call positions in the bushes. Females were collected by visual search of the bushes near the calling male.
“Hexacentrus genus is unique with their predatory nature compared to other herbivore katydids and is less studied genera in India. Their limbs bear sharp spine-like structures and mouth parts with sharp mandibles, which help them with catching and killing the prey,” Dr. Ranjana Jaiswara of Punjab University said.
Out of all three Hexacentrus species, H. khasiensis is very unique in size and sound.
“Compared to all the other Hexacentrus species, H. Khasiensis is small in size, with the female wings shorter than their full body length including the ovipositor which they use to deposit eggs. But an interesting fact is that their calling song is quite complex compared to other Hexacentrus species,” said Dr Ranjana Jaiswara.
H. khasiensis produces continuous trilling sounds with modulations in amplitude and frequency. They start with a continuous trill and after a few minutes, it changes into an alternating call between a series of low-intensity high-frequency (21kHz) pulses and a series of high-energy low-frequency (9kHz) pulses. It almost sounds like two different individual crickets calling together but recordings in the lab verified that the call was produced by a singular individual.”
Until now, this particular Hexacentrus has only been reported from the Khasi hills of Meghalaya. Based on this, the researchers have named it Hexacentrus khasiensis with respect to the Khasi hills and Khasi community who have played a role in community conservation that led them to find this species.
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“Meghalaya comes under a very interesting biodiversity region near two different zones of biodiversity, the Eastern Himalaya and Indo-Burma regions. Due to that, its biodiversity is very unique with an interesting biogeographic history relative to insects from the Eastern Himalayas and insects from South East Asia. This the possible explanation for having unique call characters in H. Khasiensis,” said Aarini.
Importance of bush cricket in ecosystem
On the importance of bush crickets in the ecosystem, Dr Ranjana said, “Ensiferans also play a strong role in the food chain ecosystem in forests and occupy a wide variety of ecological niches. Most bush crickets are herbivores, but Hexacentrus species are all carnivores.”
“Hexacentrus species prey upon a variety of smaller adult insects, eggs, or larvae. Even in the lab, we noticed that females prey upon male katydids. Bushcrickets are also preyed upon by bats, who can find their prey not only by echolocation but also by eavesdropping upon sexual advertisement calls. There is a variety of acoustically communicating predators of Ensiferans,” said Aarini.
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“The wide variety of ecological niches occupied by bushcrickets and by Ensiferans and their predators more broadly means that they can act as an indicator of the health of the forest where they are located. We can monitor the biodiversity of Ensiferans and their predators over time using noninvasive and continuous automated acoustic monitoring, and this can act as a proxy for overall biodiversity monitoring,” said Dr. Bittu.
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