FNZ 55 - Criconematina (Nematoda: Tylenchida) - Popular summary
Wouts, WM 2006. Criconematina (Nematoda: Tylenchida). Fauna of New Zealand 55, 232 pages.
( ISSN 0111-5383 (print), ; no. 55. ISBN (print) ). Published 24 Mar 2006
Nematodes or eelworms are unsegmented roundworms – predominantly microscopic. The phylum Nematoda is subdivided into the classes Secernentea and Adenophorea. Plant parasitism occurs in Tylenchida of class Secernentea (the group to which the suborder Criconematina belongs), and Dorylaimida of class Adenophorea. Plant parasitic nematodes possess a hardened mouth piece – a stylet – with which they can puncture plant cells. In Tylenchida (Tylenchina, Hoplolaimina, and Criconematina) the stylet is a stomatostyle developing from tissues of the stoma (mouth). In the Dorylaimida (Longidoridae and Trichodoridae) the stylet is an odontostyle as it develops from oesophageal tissue; their feeding on plant roots can do direct damage to their host, but they are better known for their ability to transmit plant viruses.
Many tylenchids cause damage to agricultural crops, especially in monocultures where their population numbers can build up to high levels when favoured crops are replanted in quick succession. Criconematina, the suborder of tylenchs described in this monograph, generally feed on tree roots, and their damage is restricted to commercial orchards planted with infested plant material or replanted in infested soil. In their native habitat they generally cause no damage. Of the 68 species known to be present in New Zealand, 47 are endemic (46 belonging to the subfamily Criconematinae). In the family Criconematidae the cuticle has distinct transverse striae giving the specimens a ringed appearance. In the subfamily Criconematinae these rings bear scales or spines in the females or the juveniles or both.
Criconematids are microscopic. Their characters can only be observed with the compound microscope at high magnification using immersion oil. Specimens, therefore, have to be preserved and processed by fixing in a low concentration of formaldehyde and slow saturation with glycerol and subsequent mounting on microscope slides. Criconematids are transparent and the individual species can be identified on characters inside and on the surface of the body. In Criconematina, the two sexes differ markedly (sexual dimorphism) and several of the structures of the male are poorly developed or absent. Diagnostic characters, therefore, are restricted to the females. The main internal character is the stylet. Its base has distinct knobs for the adhesion of muscles that control the movement of the stylet. Both the length of the stylet and the size and shape of the knobs are used for the identification of species. Another useful internal character is the shape of the oesophagus. External characters are the length, width, and shape of the nematode. The size of the rings of the cuticle, their total number, and the number in front of the excretory pore and posterior to the opening of the female reproductive system are also important. In species with scales and spines, their number per cuticle ring and their length can all be useful. Characters of the lip region and the shape of the scales and their various appendages can best be demonstrated with photographs taken by a scanning electron microscope.
In New Zealand, taxonomic study of nematodes started in the early 1960s. Initially it only covered free-living nematodes, but gradually plant and insect parasitic nematodes were also included. The original intention of this contribution was to summarise all studies on Tylenchida and combine them in one work. It was soon recognised, however, that this would be too extensive a task. This monograph, therefore, is restricted to the Criconematina, covering a total of 68 species, 16 of which are new to science.