 | This is not a Wikipedia article: It is an individual user's work-in-progress page, and may be incomplete and/or unreliable. For guidance on developing this draft, see Wikipedia:So you made a userspace draft. Find sources: Google (books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Conocephalus discolor
| Eortiz11/Conocephalus discolor | |
|---|---|
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Order: | |
| Family: | |
| Genus: | |
| Species: | C. discolor
|
| Binomial name | |
| Conocephalus discolor | |
Conocephalus discolor, also known as the long-winged cone-head, is a species of katydid found in marshes and meadows throughout Europe and west Asia. They are known for their characteristically long wings that extend past their abdomens. Research has been conducted in the United Kingdom for their prodigious and speedy spread from the southern coasts to areas farther north as a possible effect of climate change.
Description edit
Conocephalus discolor is a member of the genus Conocephalus, which means cone-headed. The genus name refers to the slanted face and prominent peak at the top of this insect’s head.[1] Long-winged cone-heads are so named because they have well-developed forewings that are longer than their abdomens. They are also members of the family Tettigonidae, more commonly known as katydids or bush-crickets. There is also an extra-macropterous morph, meaning that there is an even longer-winged variety of this species. This morph is more commonly found in hotter summers[2] While both types of long-winged cone-heads can fly, only the longer-winged variety can fly between distant patches.[3] Adults are green with brown wings, have red-brown abdomens (on the ventral side), and have brown stripes extending over the head and the pronotum. Most adults are also between 16 and 22 mm long. C. discolor is omnivorous, feeding mainly on grasses, but also on small insects such as aphids and small caterpillars.[4]
Reproduction and Development edit
To attract mates, male long-winged cone-heads will produce calls at significant risk to themselves, since calling increases the chances of being spotted by a predator, as well as being cuckolded by other cone-heads.[1] When a female approaches, the two insects engage in what can be described as katydid “fencing”.[5] They face each other and touch antennae in order to gauge interest and to make sure the two katydids are of the same species. It is thought that females can determine the genetic value of the male during this interaction. Typically, the female will then mount the male, after which he will curl up underneath her until he is facing the opposite direction.[1] Like all katydids, male long-winged cone-heads do not actually penetrate their mates, but instead attach a “nuptial gift” to the females. This consists of a spermatophore, a small gelatinous blob containing the sperm, and a nutritious spermatophylax, that the female consumes once the male has successfully attached it to her.[1]
There are a variety of hypotheses surrounding the significance of the attachment of the spermatophylax. One is that the spermatophylax prevents the female from eating the sperm-containing spermatophore, giving it more time for the male’s sperm to reach her eggs and increasing the likelihood of his paternity. It is thought to be a preventative measure from hungry females that might be promiscuous and mate several times in order to eat the spermatophore.[1] Another theory is that this behavior is a form of parental investment. This means that in feeding the female, the male is providing for his offspring, who would become more fit as a result of the nutritious meal. It is important to note, however, that the theories are not mutually exclusive and both may be taking place. The “nuptial gift” is also very energetically costly to the male. Males usually require at least a couple of days to recover from mating and create another gift. The size of the entire nuptial gift (including spermatophore and spermatophylax) varies widely among species, but for C. discolor, it is approximately 9.7% of the male’s body mass.[1] A typical C. discolor male at the time of reproduction weighs approximately 150 mg. It’s spermatophore weighs about 2.38 mg, and it’s spermatophylax is about 12.20 mg (averaging to about 9.7% of body mass).[6]
After the female has eaten her meal and become inseminated, she is ready to lay her eggs. C. discolor females have long and straight ovipositors, about 8-9 mm in length, which are used to spear plant stems. If the female is unsuccessful in one area, she can swivel her body around the stem and move to a more desirable location. Long-winged cone-heads prefer to oviposit in leaf sheaths and the pith of stems.[1]
Like all katydids, Conocephalus discolor is hemimetabolous. This means that when the eggs hatch, nymphs will emerge as miniature versions of the adults. Juveniles undergo a series of molts as they transform into adults and will develop wings during their final change into maturity. The number of stages (known as instars) C. discolor must go through is typically six, although this can vary due to external factors. For example, in Europe it has been seen that C. discolor goes through six instars in areas with long growing seasons (favorable climate), while going through five in mountainous areas. In areas with less beneficial environments, long-winged cone-heads will invest less resources in development.[1]
Communication edit
Like other katydids, C. discolor communicates through stridulation, the rubbing together of the forewings. On a small area of the left forewing, katydids have a rigid scraper that rubs over a file on the right wing and produces sound. The number of teeth on the file, and therefore the range of sound the insect can make, is variable dependent on the species. Sound is only produced in the closing motion of the wings, since the file and scraper do not make adequate contact when the wings open.[7] The controlled opening and closing of the forewings can lead to complex songs, most often used in attracting mates but also sometimes in predator repulsion (but usually only once the individual has been disturbed).[1] Katydids in general can control the contact between scraper and file, allowing only certain teeth to be scraped to produce different sounds. The song of C. discolor most often sounds like a faint sizzling, and can be heard 4 to 5 meters away. Audible frequencies range from 8 to 19 kHz. They are usually heard singing during the day and through sunset in the summer months, especially August.[8]
Long-winged cone-heads, like most katydids, hear through their tympana, which are located on each tibia of their forelegs. Tympana consist of a thin membrane that is stretched over an air sac that is “connected to the outside of the body via tracheal tubes."[1]
Habitat edit
C. discolor is found in low vegetation, mostly grasses and reeds (as can be evidenced by their oviposition preferences). They are found in marshes, meadows, reed beds, and sometimes swamps throughout Europe and western Asia [9], although much research has been done on their prominence and spread throughout southern England.
The long-winged cone-head was first recognized as a native species in the British Isles in 1936. Up until the 1970s, C. discolor was considered to be a rare species confined only to the southern coastal areas of the country. However, by the 1980s “it was found to be widely distributed in the New Forest and even common in quaking bogs, and during the 1990s it extended inland to Surrey and Oxfordshire and west-wards to Cornwall and is now widespread in Essex and expanding through East Anglia." [2]
In general, katydids and other Orthoptera are thought to be good indicators of climate change due to their sensitivity to temperature. They are mostly found in warmer climates and they decrease both in number and species diversity in the north. Long-winged cone-heads have specifically been thought to be indicators of climate change due to their increased range in northern Europe. Since 1975, C. discolor has spread quickly from a range mostly tied to the southern coasts of England into the central part of the country, past the river Thames.[3] This may be due to the fact that as temperatures increase, southern populations become overcrowded, and individuals spread northward in search of more resources in the newly suitable habitat.
Research shows that overcrowding of C. discolor bred under laboratory conditions led to a 50% increase in adults with significantly longer wings.[1] Therefore, changes in wing length are density dependent. Within C. discolor’s range, populations at its fringe are more likely to contain individuals with longer wings, allowing them to disperse and colonize new areas. The range core contains the more common morph with shorter wings. This difference, however, is merely temporary. Populations observed five to ten years after colonization show a population make up that is more consistent with that of the previous range core. Populations of long-winged cone-heads seem to revert to primarily short-winged morphs, despite its advantages, because of high energy costs. Female extra-macropters (extra long winged variety) have been shown to be less fertile and produce less offspring. Males also have been shown to have less reproductive success, perhaps because so much energy is needed to produce the nuptial gift that less resources can be invested in reproduction if more energy is required for the maintenance and operation of larger wings.[10] As the climate becomes more favorable, more and more long-winged cone-heads are able to reproduce, thereby dramatically increasing their populations. The frequency of extra-macropterous individuals that are capable of flying longer distances and colonizing new areas also increases. These previously uninhabited areas are now able to be colonized due to the higher temperatures preferred by C. discolor. As the range expands, frequency of extra-macropterous individuals decreases in the newly formed range core. This phenomenon has been particularly pronounced and researched in Britain.
Predators and Protection edit
Like most katydids, the primary defense mechanism of C. discolor is camouflage.[1] This species lives in low vegetation (mostly grasses and reeds, and sometimes swamps)[9], and its coloration clearly reflects that fact. Adults are green with brown wings and brown stripes[4], making them almost perfect for living in an environment with many different substrates.
The height of the grasses and reeds is also very important for the survival of C. discolor. A study conducted in the Mardyke River Valley in South Essex showed that grass that was regularly grazed by horses resulted in low sward height (less than 6 cm, on average), which in turn resulted in less abundance and diversity of several Orthopteran species, including long-winged cone-heads. There was a wider variety of Orthopteran species recorded in ungrazed pastures (average vegetation height of more than 25 cm), the most common of which was C. discolor. The abundance of each species was also significantly higher in ungrazed pastures. It is thought that this low sward height is not able to provide the protection that long-winged cone-heads require from both inclement weather and predators.[11]
In addition to the predators most katydids are vulnerable to (such as birds), C. discolor is also vulnerable to other vicious insects and parasites. C. discolor, as well as other members of Conocephalus, can be victims to wasps of the family Sphecidae, which include digger wasps. Digger wasps are mainly solitary parasitoids that sting and then drag their paralyzed prey to their underground nests. The katydids are then given to the wasps’ larvae. The katydid is alive, but paralyzed and is slowly consumed alive by the larvae. Digger wasps usually burrow their nests in relatively close proximity to other digger wasps. One typical colony of approximately one hundred sphecid wasps can devour several thousand Conocephalus.[1]
Another parasitoid that affects conocephalines, as well as C. discolor since they usually live near water, are horsehair worms (Gordius aquaticus and Gordius robustus). These worms devour their hosts from the inside out, keeping their vital functions going for as long as possible. Adult worms mate and lay eggs in water, which are subsequently eaten by an aquatic insect that serves as an intermediate host. These aquatic insects are then eaten by C. discolor, which acts as the final host and the food source for the fully formed worm. Eventually, all that remains inside the final host are the adult worms and the katydid’s alimentary tract.[1]
References edit
- ^ a b c d e f g h i j k l m n Gwynne, D.T. 2001. Katydids and bush-crickets: reproductive behavior and evolution of the Tettigoniidae. Cornell University Press, Ithaca, NY.
- ^ a b Marshall, J. 2010. “Grasshoppers, Crickets, and Allied Insects.” Silent Summer: The State of Wildlife in Britain and Ireland. Ed. Norman Maclean. Cambridge University Press. Pgs 531-539
- ^ a b Reemer, M., P.J. van Helsdingen & R.M.J.C. Kleukers (editors) 2003. Proceedings of the 13th International Colloquium of the European Invertebrate Survey, Leiden, 2-5 September 2001. EIS- Nederland, Leiden
- ^ a b Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: the genera of Orthoptera. Conocephalus Thunberg. Version: 1st December 2010. http://delta-intkey.com/britin/ort/www/conoceph.htm
- ^ Fabre, J. H. 1917. The Life of the Grasshopper. Hodder and Stoughton, London.
- ^ Vahed, K., Gilbert, F., 1996. Differences across Taxa in Nuptial Gift Size Correlate with Differences in Sperm Number and Ejaculate Volume in Bushcrickets (Orthoptera: Tettigoniidae). Proceedings: Biological Sciences, Vol. 263, No. 1374, pp. 1257-1265
- ^ Walker, T. J. 1975. Stridulatory movement in eight species of Neoconocephalus (Tettigoniidae). J. Ins. Physiol. 21: 595-603
- ^ Oliveira, P. A. P., Simoes P.C., Quartau J.C. 2001, Calling songs of certain orthopteran species (Insecta, Orthoptera) in southern Portugal. Animal Biodiversity and Conservation. 24.1
- ^ a b JRank Animal Life Resource. (Animal Encyclopedia) http://animals.jrank.org/pages/2376/Grasshoppers-Crickets-Katydids-Orthoptera-LONG-WINGED-Cone-Head-Conocephalus-discolor-SPECIES-ACCOUNTS.html
- ^ Simmons, A.D., Thomas, C.D. 2004. Changes in Dispersal during Species’ Range Expansions. The American Naturalist. Vol. 164, No. 3. pp. 378-395
- ^ Gardiner, T., Haines, K. 2008. Intensive grazing by horses detrimentally affects orthopteran assemblages in floodplain grassland along the Mardyke River Valley, Essex, England. Conservation Evidence 5, 38-44