A rapid method for the estimation of mean dry weight and lipid content of the infective juveniles of entomopathogenic nematodes using image analysis

AbstractA 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 digitalised and transferred to a computer for analysis. The longitudinal cross-sectional area of the nematode (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 x 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. Methode rapide pour l'estimation du poids sec et du contenu lipidique moyens des juveniles infestants de nematodes entomopathogenes basee sur l'analyse d'images - Il est decrit une methode utilisant l'analyse numerisee d'images et permettant l'estimation du poids sec, du contenu lipidique, de la taille et de la longueur du corps des juveniles infestants (IJ) de nematodes entomopathogenes. Les images des IJ, saisies par video-camera, sont digitalisees et transferees pour analyse sur ordinateur. La surface de la coupe longitudinale du nematode (Area), le niveau moyen d'opacite (MGL) et le perimetre de l'image du nematode (Perimeter) sont mesures automatiquement. Des echantillons de nematodes de taille, de poids sec et de contenu lipidique varies ainsi qu'une serie representant differents ages ont ete examines. Il a ete constate que: i) l'index Area x MGL est bien correle au poidsmoyen du nematode, lequel represente un bon indicateur de la reserve energetique totale du nematode; ii