SUMMARYThe aim of this review was to undertake a survey of researchers working with plant-parasitic nematodes in order to determine a 'top 10' list of these pathogens based on scientific and economic importance. Any such list will not be definitive as economic importance will vary depending on the region of the world in which a researcher is based. However, care was taken to include researchers from as many parts of the world as possible when carrying out the survey. The top 10 list emerging from the survey is composed of: (1) root-knot nematodes (Meloidogyne spp.); (2) cyst nematodes (Heterodera and Globodera spp.); (3) root lesion nematodes (Pratylenchus spp.); (4) the burrowing nematode Radopholus similis; (5) Ditylenchus dipsaci; (6) the pine wilt nematode Bursaphelenchus xylophilus; (7) the reniform nematode Rotylenchulus reniformis; (8) Xiphinema index (the only virus vector nematode to make the list); (9) Nacobbus aberrans; and (10) Aphelenchoides besseyi. The biology of each nematode (or nematode group) is reviewed briefly.

In Europe, root-knot nematodes are increasingly important. Out of more than 90 Meloidogyne species currently described, 23 have been found on the continent. In the cooler climates, Meloidogyne hapla, M. naasi, M. chitwoodi and M. fallax are prevalent. Meloidogyne arenaria, M. javanica and M. incognita are the most common species in warmer conditions of southern Europe, but also in glasshouses in northern Europe. Morphological identification of root-knot nematodes is difficult and time consuming; therefore, many research groups have been developing molecular techniques for identification of Meloidogyne species. Meloidogyne chitwoodi and M. fallax are quarantine organisms and subject to regulations, and the highly aggressive M. enterolobii has been added to the EPPO alert list. Differences between temperate and tropical Meloidogyne species and their prevalence in Europe imply the need for different management strategies in south and north Europe. Possible crop rotations for the control of root-knot nematodes are limited due to the wide host range of several important species. The banning of methyl bromide and restrictions on other fumigant pesticides in the EU have increased the application of biofumigation significantly in south Europe. The egg-parasitising fungus Paecilomyces lilacinus is commercialised in Germany and applied as dispersible granules for application in water. Intensive research is conducted on the eggparasitising fungus Pochonia chlamydosporia, and the obligate parasitic bacterium Pasteuria penetrans. European research has paid much attention to resistance breeding and selection. The Mi gene of tomato is widely used but resistance-breaking populations of M. incognita and M. javanica have been reported in different countries.

The encounter between Meloidogyne species and tomato is many centuries old. Meloidogyne species are known to cause high levels of economic loss worldwide in a multitude of agricultural crops, including tomato. This review was initiated to provide an overview of the damage potential of Meloidogyne spp. on cultivars of tomato (Solanum lycopersicum), and to compile the different studies done on the management of Meloidogyne spp. on tomato with particular emphasis on the Mi resistance gene. Numerous studies have been conducted to assess the damage potential of root-knot nematode on various tomato cultivars; its yield loss potential ranges from 25 to 100%. A range of management options from using synthetic nematicides to soilless cultures have been tried and are available for managing Meloidogyne spp. Resistant commercial cultivars and rootstocks carrying the Mi gene have been used successfully to manage Meloidogyne incognita, M. javanica and M. arenaria. However, virulent populations have been detected. Relying on a single root-knot nematode management strategy is an outdated concept and different management options should be used in an integrated management context by considering the whole system of disease management. In future management of Meloidogyne species, care must be taken in directly extrapolating the tolerance limit determined elsewhere, since it is affected by many factors such as the type of initial inoculum and physiological races of Meloidogyne spp., environmental conditions, types of cultivars and experimental approaches used.

Laboratory assays using artificial diet demonstrated that tebufenozide (RH‐5992) and the new structural analogue, RH‐2485 (proposed common name methoxyfenozide), possess strong ecdysone‐like activity against last‐instar larvae of the beet armyworm, Spodoptera exigua, and the cotton leafworm, Spodoptera littoralis, leading to precocious lethal moulting. LC50 values showed that the activity of RH‐2485 (0.38 mg AI litre−1) was about twice that of tebufenozide (0.60 mg AI litre−1) in S. exigua, whereas in S. littoralis respective LC50 values were 1.15 mg AI litre−1 and 9.51 mg AI litre−1. The retention‐fate curves of 14C‐radiolabelled ecdysone agonist could not explain the differential toxicity values between species and compounds. Ingestion of the oxidase inhibitor piperonyl butoxide (PB) synergized the toxicity of the ecdysone agonist, indicating the importance of oxidative detoxifcation in Spodoptera larvae, and may raise the possible use of PB as synergist for this group of insecticides, or for monitoring resistance due to increased oxidation. © 1999 Society of Chemical Industry

The root-knot nematodes, Meloidogyne chitwoodi and M. fallax, cause severe damage to economically important crops and, in 1998, both species were listed as quarantine pests in Europe. Comparative studies were made on the effects of root diffusates and host age on the in vitro hatching of M. chitwoodi and M. fallax. There is a marked contrast in the hatching response of the two species. Hatching of second-stage juveniles (J2) of M. chitwoodi produced on young plants did not require host root diffusate stimulus, whereas at the end of the plant growing season, egg masses contained a percentage of unhatched J2 that require host root diffusate to cause hatch. This form of obligate quiescence at the end of the host growing season was not found in M. fallax. This species hatched well in water and did not require hatch stimulation from root diffusate, irrespective of the age of the plant on which the egg masses were produced. The number of eggs per egg mass for M. fallax collected on senescing plants was significantly greater than the number of eggs per egg mass for M. chitwoodi. The number of eggs per egg mass of M. chitwoodi decreased with plant age. The results are discussed in the context of the differing survival strategies of the two species.