Saturday, 28 December 2013

Silent Crickets

Most people are aware that crickets produce sounds. We normally hear the "calling song", that is the sounds produced to attract females. Crickets can produce other sounds announcing territoriality or post-mating sounds. It has been shown that the calling songs are highly species specific. That is females are “tuned” to answer the calls of males of their own species. Singing by romantic males of other species just go “over their heads”!

Females of some mole crickets, family Gryllotalpidae, can produce songs, thereby answering calling males but females of the typical crickets, family Gryllidae, are silent.

However, there are cricket species where neither sex produce any sounds at all. How and why this happens in evolutionary terms is often debated. Some of the ideas advanced include the obvious complexity of sounds in a particular kind of environment—perhaps, one with many cricket species or living in a odd place where sounds are not needed or desired e. g.—caves, for example where hungry bats may home in on a singing insect. In such a situation, males would be “selected” by the predator and this would put the population at risk. Being quiet may have its advantages.

How do silent crickets find one another? Perhaps, they find each other using chemical or visual signals.

Here in my rainforest I have discovered some 53 species of Gryllidae, give or take a few. Of this number some 35% are silent; they produce no sounds at all. Is this absence of sound production associated with living in the rainforest environment with the complexity of leaves, trees, shrubs, rocks etc. Maybe leaves, shrubs etc reverberate and interfere with the calling song. In such circumstances, maybe chemical signals get the sexes together. The population numbers of rainforest crickets that don't sing seems higher than one observes elsewhere, so calling by song may not be as important as it is where populations are dense. Cicada species seem to solve this problem by singing different times of the day and evening and singing during different seasons. 

Here is a list of the non-singing species recorded at my site

F=Flightless, LW=long-winged, capable of flight. A few species have both long-winged and short-winged (flightless) morphs. Silvinella species live on the forest floor in leaf litter. Both sexes are wingless. Most of the other are active on leaf surfaces at night. Euscyrtus lives in deep grasses and seems more active during the day.
Aphonoides australis (Walker) LW
A. lowanna Otte & Alexander LW
A. weeronga Otte & Alexander or near LW
A. debilis (Chopard) LW
A. sp nov. 1 LW
A. sp. nov. 2 LW
Genus nr Riatina (stridulatory file?) LW
Euscyrtus hemelytrus (Haan) F, LW
Umbulgaria hillimunga Otte & Alexander LW
Silvinella warraninna Otte & Alexander F
Amusurgus noorundi Otte & Alexander F
A. hackeri (Chopard) LW
A. kanyakis Otte & Alexander LW
A. minmirri Otte & Alexander LW
A. tinka Otte & Alexander LW
Metioche vittaticollis (Stål) F & LW
Trigonidium bundilla Otte & Alexander F
Trigonidium ?australiana (Chopard) F
T. killawarra or near Otte & Alexander F
Some examples.
Gryllidae; Pteronemobiinae; Silvinella wirraninna female
Gryllidae; Trigonidiinae; Amusurgus mubboonis Otte and Alexander male

 Gryllidae: Trigonidiinae; Amusurgus tinka female

Gryllidae; Trigonidiinae; Amusurgus hackeri (Chopard) female

Gryllidae; Trigonidiinae; Trigonidium bundilla male
Note the absence of a stridulatory file on the right wing on this and the other males below.
Gryllidae; Eneopterinae; Podoscirtini; Aphonoides sp 1 male
Gryllidae; Eneopterinae; Podoscirtini; Aphonoides sp prob australis

Gryllidae; Eneopterinae; Podoscirtini; Aphonoides weeronga male

Gryllidae; Eneopterinae; Podoscirtini; Aphonoides lowanna male light morph
Gryllidae; Eneopterinae; Podoscirtini; Aphonoides lowanna male dark morph
Gryllidae; Eneopterinae; Podoscirtini; Euscyrtus hemelytrus male

Gryllidae; Eneopterinae; Podoscirtini; Euscyrtus hemelytrus female

Tuesday, 10 December 2013

The Peppermint Stick-insect

Tis the Season. So why not the Peppermint Stick-insect. It is unlike the traditional peppermint stick in that it is not red and white. Here is its story.

Click on the photos to enlarge
Typical resting position of a female Peppermint Stick in the mid-rib of Pandanus.

The Peppermint Stick-insect, Megacrania batesii (Kirby 1896) Phasmatidae; Platycraninae is one of the insect icons of the Daintree Rainforest region of far north coastal Queensland, Australia. Tourist operators know of at least two populations that provide impressive displays.
The fore and middle legs are forward with the antennae in between. Not the short forewings.

Although described over 100 years ago, these insects went unnoticed until relatively recently. My predecessor at CSIRO, Ken Key, showed me some ancient specimens in the collection from islands in the Gulf of Carpentaria but he said he had heard that the species was in the Daintree region in the far north. But nothing was known of its habits so it was with great excitement in the early '90's that I found a population in the Cape Tribulation area. I learned later that Jack Hasenpusch knew of a population at Etty Bay.
Resting in the heart of a spiny Pandanus. Note the feeding damage in the foreground. It would be a brave bird or lizard that would attempt to extract this individual.

This stick insect is associated with Pandanus. There are several species of Pandanus but this insect seems to prefer only one, P. tectarius. P. tectarius has a very broad distribution occurring along the the coast and inland for a considerable distance. So it was logical to assume that the sticks could be found elsewhere. But this is not the case. Diligent searching for many years of every Pandanus has failed to locate additional populations of the species. Where these insects occur they are numerous and the plants they live in have a distinct appearance. The leaves are chewed to the mid-rid in characteristic semicircular patterns.
"Paired up" The female is the larger individual on the bottom. This is a large insect, roughly the length of a pencil and slightly broader. Note that the pair is not mating. Males seem to "stake out" females and ride around on their backs. They are therefore available for mating whenever. Behaviourists would suggest that the male is therefore, protecting his offspring from being cuckold by other males. 
A pair of Peppermint Sticks. Note they are not attached.

The sticks have a rather simple biology. They never stray from their host plants even though they are winged and could probably fly or at least glide a bit. This species was described originally from the Solomon Islands and New Guinea and the Bismarck Archipelago. That may give some clue to the distribution of the stick.

The sticks live in the mid-rib of the Pandanus leaf. They scuttle back and forth and are highly perceptive of external activities. As soon as they detect the presence of danger, they retreat backwards into the base of the leaf protected from intruders by the spiny hooks along the sides of the leaves. They move using the fore and middle legs and use the hind legs only to move from one leaf to the other.

The droppings (frass) accumulates in the base of the leaves along with the many eggs females produce. During cyclones masses of Pandanus get dislodged and float out to sea. The sticks probably die during this time but the eggs may be safely carried to a new destination tucked in the axils of the leaves.
Frass accumulated inside at the base of the pandanus leaves. It is early in the season so there are few or no eggs there at this time.

An additional advantage to the stick is that it is probably facultatively parthenogenetic. That means that unmated females can lay eggs that hatch. In fact, it seems to be the case that the populations south of the Daintree region. Apparently no males have been found in these populations.
A late instar nymph, more blue than green.

A last instar female nymph. +Note the developing wing buds of the fore and hind wings. Also note the feeding damage to the plant.

Peppermint Sticks are diurnal. They have well developed eyes and are well aware of their surroundings. When suitably threatened, they squirt a white milky substance from the corners of the thorax at the intruders. The smell is reminiscent of peppermint. Hence the name!

A disturbed individual. The white spots are the points where the peppermint-smelling fluid is exuded as a spray. 

Seasons Greetings from the Peppermint Sticks and Bunyipco.