The ectoparasitic nematodes 



Aitnougn most genera of the Tylenchida and the piant-parasitlc 

 doryiainis are represented by one to several species in Western Europe 

 only a few of these species have been found up to now to be of econ- 

 cmin importance. Tney are Hoplolaimus uniformis and a Paratylencnus 

 species. 



Hoplolaimus unifoimis 



Although this nematode has a wide host range, until now only 

 carrots and lilies (Slootweg 1956) have been shown to suffer from its 

 attack. It seems to make peas susceptible to a secondary attack, most 

 probably by the fungus Fusarium oxysporum var. pisi race 2. Tnis com- 

 plex causes early yellowing, wnereas tne nematodes alone even in high 

 concentrations do not damage the peas although they live on its roots 

 (SEIWHORST 19i>U, LAERUY^^KE and SEIlMHORST 195U). 



In pot experiments some of the other hosts appeared to build up 

 very large populations of the eelworro in the soil e.g. chicory, cauli- 

 flower and beets. They were not found to suffer in the field and for 

 the most part they do not even have any particular influence on popu- 

 lation num.bers there. 



This again is most probably due to the inf 'uence of the soil. 

 Hoplolaimus uniformis is most abundant in iignt sandy soils with a 

 ratti?r hign humus content. It was never found in clay soils except 

 occasionally m low numbers. Here spiral nematodes of the genus 

 J-'otyiencnus ( Helicotylencnus , Gottnoldstemeria ) may be abundant. On 

 arable land either Hoplolaimus uniformis or spiral nematodes may be 

 abundant but never both. 



In winter sown carrots damage can be expected at degrees of in- 

 festations over h)00 specimens per ijOO g, of soil. In spring sown 

 carrots this number is higher, 



Paratyienchus species 



Various species of this genus are widely distributed in all soil 

 types, but only very occasionally they occur in numbers high enough 

 to cause damage (more tnan 10,000 per 500 g. of soil). 



Damage has been described in carrots (WElSCHER, 1957) and celery 

 (OOSTti'wyRlwK, 1953) probably caused by the same species. The damage 

 in carrots can be distinguished from tnat by Hoplolaimus uniformis 

 by the rusty aopearance of tne roots and tne younfi carrot, '-.'hen at- 

 tacked by H. uniformis they look giaylsh. 



Although apparently there are factors wnich localize the damage 

 by Paratyienchus , nothing is known about the influence of soil type 

 or treatment. 



