A new species of entomopathogenic nematode, Steinernema guangdongense sp. n. was recovered from a soil sample collected from Jijia town in the western part of Guangdong province, the Peoples Republic of China during a survey for entomopathogenic nematodes in 2001. The nematode can be separated from other described species of Steinernema, by morphological, morphometrical characteristics of different stages of the nematode, by crossbreeding tests and by characterizations and phylogeny of DNA sequences of either a partial 28S or the internal transcribed spacer regions of rDNA. This nematode is closest to S. longicaudum. It can be distinguished from that nematode by characteristics of different stages. For infective juveniles, although the body length is almost similar (1055 μm compared to 1063μm), body diameter of the new species is larger; values of EP (length from anterior end to excretory pore), NR (length from anterior end to nerve ring) and a body length/body width ratio are smaller, and tail with dorsal constriction. For male, the new species has longer spicule, not well curved, spicule head shorter, shaft not prominent or absent and spicule tip not suddenly tapered as shown in S. longicaudum. Also, the ratios SW (spicule length/anal body width) and GS (gubernaculums/spicule) are smaller. For female, the presence of a small double flapped epiptygma, a small projection on dorsal side of the tail tips and prominent post-anal swelling is typical for the new species.

Summary-A method using computer image analysis for the estimation of dry weight, lipid content, body size and length of individual infective juveniles (IJ) of entomopathogenic nematodes (EN) is described. Images of IJ, captured using a video camera, were digitalized and transferred to a computer for analysis. The longitudinal cross-sectional area of the nemat ode (Area), mean grey level (MGL) and perimeter of the nematode image (Perimeter) were measured automatically. Nematode samples having a range of sizes, mean dry weights and lipid contents, as well as a series of samples of different ages were examined. It was found that: i) the index Area £ MGL correlates well with the mean dry weight of the nematode, which is in turn a good indicator of the total energy reserve of the nematodes; ii) MGL correlates well with the lipid content (as % dry weight) which is a good indicator of the quality of the energy reserve; and iii) the perimeter of the nematode image can be used to estimate the length of an IJ. Compared to currently available methods, such as direct measurement of mean dry weight or lipid content, computerised image analysis gives more information concerning the samples tested and enables variations in dry weight, lipid content, body size and length between individual IJ to be estimated readily. A sample of 30 IJ can be examined in 30 to 60 min making this method ideal for quality control during production, processing, formulation and storage of EN-based biopesticide products. Résumé – Méthode rapide pour l’estimation du poids sec et du contenu lipidique moyens des juvéniles infestants de nematodes entomopathogènes basée sur l'analyse d'images-Il est décrit une méthode utilisant l'analyse numérisée d'images et permettant l'estimation du poids sec, du contenu lipidique, de la taille et de la longueur du corps des juvéniles infestants (IJ) de nematodes entomopathogènes. Les images des IJ, saisies par vidéo-camera, sont digitalisées et transférées pour analyse sur ordinateur. La surface de la coupe longitudinale du nématode (Area), le niveau moyen d'opacité (MGL) et le périmètre de l'image du nématode (Perimeter) sont mesurés automatiquement. Des échantillons de nématodes de taille, de poids sec et de contenu lipidique variés ainsi qu’une série représentant différents ages ont été examinés. Il a été constaté que: i) l'index Area£ MGL est bien corrélé au poidsmoyen du nématode, lequel représente un bon indicateur de la réserve énergétique totale du nématode; ii) MGL est bien corrélé au contenu lipidique (en % du poids sec), bon indicateur de la qualité de la réserve énergétique; iii) le périmètre de l’image peut être utilisé pour estimer la longueur des IJ. Comparée aux méthodes couramment utilisées-telle la mesure directe du poids sec et du contenu lipidique moyens-l'analyse numérisée des images donne une meilleure information sur les échantillons testés et permet une estimation rapide des variations individuelles du poids sec, du contenu lipidique, de la taille et de la longueur des IJ. Un échantillon de 30 IJ peut être examine en 30 à 60 min ce qui rend cette méthode idéale pour les contrôles de qualité pendant la production, les traitements, la formulation et le stockage des produits biopesticides à base de nématodes entomopathogènes.

Energy metabolism and its relation to survival of the infective juveniles (IJ) of S. carpocapsae under anaerobic and oxygen-deficient conditions were studied by monitoring changes in survival rate, levels of key energy reserve materials, oxygen consumption, and respiratory quotient (RQ). The effects of various factors on the survival of IJ under anaerobic conditions were also investigated. Under anaerobic conditions, the IJ were inactivated but could survive for several days in an immobile state, using the carbohydrate reserves glycogen and trehalose for energy supply. The survival time of IJ was mainly dependent on the availability of energy supply, which, in turn, was influenced by factors such as temperature and metabolic by-products. Surviving, anaerobically incubated IJ fully recovered upon return to aerobic conditions. Recovering IJ were characterized by regaining mobility and restoration of carbohydrate reserves consumed during the anaerobic period. Carbohydrate reserves were restored by conversion from lipid reserves and possibly from anaerobic metabolic by-products. The infectivity of IJ recovered from the anaerobic state was not affected. At 1% oxygen level, IJ were also immobile and mainly depended on carbohydrate reserves for energy supply and the RQ was greater than 1. However, some oxygen was consumed; the survival time of these IJ was shorter than those kept in natural air but longer than those under anaerobic conditions. When IJ were incubated at oxygen levels of 3% to 21%, the RQs were maintained at 0.7 to 0.8. Oxygen consumption rates and the reduction in both mean dry weight and lipid levels were proportional to oxygen levels while the survival time of IJ was inversely proportional to oxygen levels.

Two hypotheses on the synthesis of the protectants glycerol and trehalose of the infective juveniles (IJs) of Steinernema carpocapsae during osmotic dehydration were tested and utilised to evaluate the function and importance of glycerol on survival of the nematodes during osmotic dehydration. This was achieved by comparing the changes in survival, morphology, behaviour and levels of glycerol, trehalose and permeated compounds of the IJs dehydrated in seven hypertonic solutions at two temperature regimes: (1) 5 8C for 15 days; and (2) 23 8C for 1 day followed by 5 8C for another 14 days. The results substantiate both hypotheses tested: (1) the permeability of the IJs to various compounds, such as sucrose or ethylene glycol, when they are dehydrated in hypertonic solutions of these compounds; and (2) suppression of the synthesis of protectant glycerol but not trehalose when IJs are dehydrated at low temperature. The results also showed that: (1) although trehalose was the preferred dehydration protectant, glycerol played an important role in rapidly balancing the osmotic pressure when IJs were exposed in hypertonic solutions; (2) the presence of glycerol was essential for the IJs to survive and function properly even under moderate osmotic dehydration, especially when IJs were dehydrated in salt solutions; and (3) some exogenous compounds permeated into IJs during osmotic dehydration such as ethylene glycol, may function in the same way as glycerol and significantly improve the survival and function of the IJs. The results indicate that each of the protectants glycerol and trehalose has a specific function and neither is replaceable by the other.