Tuesday, 14 April 2015

Tripius gyraloura, a Sphaerularid Nematode infecting the Arundo Gall Midge.

Sphaerularid Nematodes are highly virulent parasites of Insect hosts. While most parasites seek to keep their host alive for as long as possible, enabling them to live and produce offspring for as long as possible, Sphaerularids begging to reproduce at a high rate shortly after entering a new host,  producing a large number of young which quickly overcome the host. While some of these young may exit the host while it still lives and start seeking out new hosts, the majority will exit the host after its death.

In a paper published in the journal Systematic Parasitology on 1 November 2014, George Poinar of the Department of Zoology at Oregon State University and Donald Thomas of the United States Department of Agriculture-Agricultural Research Service Cattle Fever Tick Research Laboratory, describe a new species of Sphaerularid Nematode infecting the Arundo Gall Midge, Lasioptera donacis.

Gall Midges lay their eggs within the tissues of plants, where they cause the plant to form a gall, in which the larval Midge lives, surviving on the plant’s natural fluids and protected from predators by the gall. The larval stage of the Insect lives its entire life within the gall, emerging from the egg, and growing till it is ready to pupate, which it does within the gall. Only the adult stage emerges to mate and lay eggs on new hosts. High levels of Gall Midge infections are harmful to plants and may even kill them, and species of Gall Midge are often capable of infecting only a single species of plant, making them of great interest to biologists looking for control species for invasive plants (plants which have been introduced to new environments by human activities, and lacking natural predators in these environments, become to dominate them and exclude native flora and fauna).

The Arundo Gall Midge, Lasioptera donacis, is a natural parasite of the Old World Giant Reed, Arundo donax, a species native to waterways of the Mediterranean Basin, but introduced to North America by European settlers in the sixteenth century, where it has become a serious invasive pest, as it lacks natural predators or parasites in the New World, and has an ability to modify and dominate aquatic ecosystems. As such the Arundo Gall Midge is considered to be a potential biological control for the Giant Reed, and is being studied at a quarantined laboratory run by the United States Department of Agriculture at Moore Air Base at Edinburg, Texas, with a view to releasing it into American ecosystems.

Midges were imported to Moore Air Base inside the stems of infected Giant Reeds harvested in France, Italy and Greece. Many of these Midges were found to be infected with a virulent Sphaerularid Nematode, which suppressed the reproductive ability of, and eventually killed its hosts. Such parasites have important implications when trying to establish control species for invasive pests. On the plus side, if the biological agent proves capable of switching to unintended hosts and itself becomes an invasive species, the parasite can be used to control it, but on the minus side, if the parasite is accidentally releases with the control species, it can prevent it from becoming established, thereby undermining the control effort, or worse still, the parasite may itself prove capable of switching to a new host (or hosts) in its new home, further damaging an already vulnerable ecosystem (and eradicating a new parasitic Nematode, once released, is almost impossible).

The new Nematode is placed in the genus Tripius, and given the specific name gyraloura, meaning ‘round-tail’. The species has a free-living sexual stage, which seeks out new hosts to infect, but does not feed independently or infect a secondary host (many parasites have more than one host in their life-cycle, and thus have primary and secondary, and sometimes even tertiary hosts). The free-living females reach 297–360μm in length and have a well-developed stylet (a hollow mouthpart similar to a hyperdermic needle), while the males reach 415–428μm and have an underdeveloped stylet. These mate in the environment, whereupon the males die and the females seek out a new host, using secretions to penetrate the body wall of juvenile Midges shortly before pupation. The infective female everts her uterine cells into the host’s haemocoel, giving birth to secondary, parasitic females, which can reach 0.6-2.0 mm in length, and which produce asexually, giving birth to larvae 290-430 μm in length. Sexual reproduction in infected Midges emerging form their pupas appeared to be supressed, and the Midges soon after, revealing body cavities packed with Nematodes. Some of these may have escaped through the ovipositors of female hosts, but most are thought to have escaped after the host’s death.

Tripius gyraloura. (1) Cluster of parasitic juveniles (arrow) in a dissected female Lasioptera donacis (arrowhead shows anterior end of a mature parasitic female); (2) free-living infective stage female. Scale-bars: (1) 144 μm; (2) 39 μm. Poinar & Thomas (2014).

As well as being of interest due to its potential impact on the biological control program for the Old World Giant Reed, the discovery of Tripius gyraloura is interesting because it isonly the second such infection in a living Gall Midge discovered, one other member of the same genus Tripius gibbosus infects the Gall Midge Cecidomyia pini, while a third member of the genus infects Sciarid Flies. A Gall Midde infected with parasitic Nematodes is also known from Eocene Baltic Amber.

See also…

http://sciencythoughts.blogspot.co.uk/2015/04/philometrid-nematodes-from-perciform.htmlPhilometrid Nematodes from Perciform Fish off the north Australian coast.                 Philometrids are large Nematodes parasitizing Fish . They show a high degree of sexual dimorphism, with males typically only a few mm in length, while females may reach tens of...

Capillariid Nematodes are parasitic worms infecting a variety of different Vertebrate hosts. The group is split into 22 genera, of which nine are parasites of Fish. Members of the genus Capillaria cause infections in...

Pinworms, Oxyuridae, are parasitic Nematodes infecting the digestive tracts of Mammals. They have short life cycles, typically undergoing several generations in a year, with eggs being released in the host’s faecal matter to infect new hosts. Some species of Pinworm appear to be quite cosmopolitan, infecting...




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