''Cornops aquaticum'' is a semiaquatic
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
grasshopper
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Grasshopp ...
native to the
Neotropics
The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropics, tropical Ecoregion#Terrestrial, terrestrial ecoregions of the Americas and the entire South American temperat ...
, from southern Mexico south to central Argentina and Uruguay.
It feeds and breeds exclusively on members of the aquatic plant family
Pontederiaceae
Pontederiaceae is a family of flowering plants.
The APG IV system of 2016 (unchanged from the APG III system of 2009, the APG II system of 2003 and the APG system of 1998) places the family in the order Commelinales, in the commelinid clade, in ...
, especially
water hyacinth
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.[biological pest control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...]
agent for the water hyacinth in countries where that plant is
invasive.
Although its semiaquatic behavior is unusual, it is not unique. In South America alone there are more than 50 species of
orthoptera
Orthoptera () is an order of insects that comprises the grasshoppers, locusts, and crickets, including closely related insects, such as the bush crickets or katydids and wētā. The order is subdivided into two suborders: Caelifera – grassho ...
ns that are associated with water, including a few relatively well-known species like ''
Paulinia acuminata'', which is used for control of the plant ''
Salvinia molesta
''Salvinia molesta'', commonly known as giant salvinia, or as kariba weed after it infested a large portion of Lake Kariba between Zimbabwe and Zambia, is an aquatic fern, native to south-eastern Brazil. It is a free-floating plant that does ...
''.
Appearance
''Cornops aquaticum'' is a medium-sized grasshopper, with adults typically about in total length (head to wing tip); males average smaller than females.
[ Adults are greenish with a distinct, broad black stripe on either side, running from the eye to the tip of the wing.][Lin Besaans (2011). . Plant Protection Research Institute, Department of the Environment (South Africa). Accessdate 17 March 2019.] During dry periods they become brown. The nymphs
A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are typ ...
range from , and are mottled in green-blue and orange-red.[
]
Ecology
Being semiaquatic and living on floating plants, both adults and nymphs of ''C. aquaticum'' are a strong swimmers and readily enter the water.[ They have been observed moving between aquatic plants as much as below the surface. If on land and seeing a predator like a bird, the grasshopper may attempt to crawl out of sight, jump or fly away, or dive into the water where it may stay submerged for an extended period of time.] The adults are strong fliers and can move relatively long distances to access new regions with their preferred food plants.[
Adults live for 55–110 days;][ after an initial feeding period of four weeks, females deposit up to seven egg packets at intervals.] Each packet contains 30–70 eggs.[ The female inserts its ]ovipositor
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
into the leaf stalk of the host plant to deposits the egg packet; the egg cases are large, measuring an average of .[ The eggs hatch after 25–30 days,][ and the nymphs feed on the leaves of the plant for about seven weeks, passing through six or seven ]instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
s, and causing much damage.[ Feeding trials show that besides ]water hyacinth
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.[Eichhornia azurea
''Pontederia azurea'' is a water hyacinth from the Americas, sometimes known as anchored water hyacinth. It is the type species of ''Pontederia'' subg. ''Eichhornia'', which was previously recognized as part of the polyphyletic genus Eichhornia. ...]
'' and ''Pontederia cordata
''Pontederia cordata'', common name pickerelweed (USA) or pickerel weed ( UK), is a monocotyledonous aquatic plant native to the American continents. It grows in a variety of wetlands, including pond and lake margins across an extremely large ...
'' (pickerel weed), both also in the family Pontederiaceae
Pontederiaceae is a family of flowering plants.
The APG IV system of 2016 (unchanged from the APG III system of 2009, the APG II system of 2003 and the APG system of 1998) places the family in the order Commelinales, in the commelinid clade, in ...
, and on ''Canna indica
''Canna indica'', commonly known as Indian shot, African arrowroot, edible canna, purple arrowroot, Sierra Leone arrowroot, is a plant species in the family Cannaceae. It is native to much of South America, Central America, the West Indies, and ...
''.[ In laboratory starvation trials, nymphs can also feed on some other plants but the females do not oviposit on these species and the nymphs do not develop beyond the third instar on any of them. The adults also consume large amounts of foliage of their plant host.][ Damage caused to the plant is high compared to damage caused by other grasshoppers, but nevertheless, it is only able to limit the plant, as the growth exceeds the consumption by the insect.]
Biological control
The water hyacinth is an aquatic plant in the family Pontederiaceae whose natural enemies keep under control in its native South America. However this plant has been introduced into countries where it has insufficient natural enemies and where it has become invasive. ''Cornops aquaticum'' is under consideration as a biological control agent for this invasive plant, and has been introduced under controlled conditions into South Africa for this purpose. Before full release, the South African trials showed that, in the absence of ''E. crassipes'', the adult insects would feed on maize
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
(''Zea mays'') and sugarcane
Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...
''(Saccharum officinarum)'', but that only eggs laid on ''E crassipes'' were viable. Where the insects had a choice of diet, they invariably chose ''E. crassipes'' and were not found on the crop species.
References
{{Taxonbar, from=Q10459808
Acrididae