ÉLEVAGE SUR MILIEU ARTIFICIEL SIMPLE DE DEUX NOCTUELLES PARASITES DU COTON EARIAS INSULANA ET SPODOPTERA LITTORALIS

Résumé L'élevage des chenilles de Earias insulana Boisd. et de Spodoptera littoralis Boisd. est réalisé sur un milieu artificiel simple ayant déjà permis d'élever 18 autres espèces de Lépidoptères Noctuidae. Les chenilles d' E. insulana sont élevées individuellement pendant tout le développement; tandis que les chenilles de S. littoralis sont élevées en groupe pendant les premiers stades et individuellement pendant les derniers stades. Respectivement pour chacune des deux espèces, 9 et 25 générations sont réalisées pour les souches qui se sont maintenues le plus longtemps. La technique d'élevage est décrite et les résultats obtenus sur milieu sont comparés à ceux obtenus par différents auteurs dans d'autres conditions d'alimentation. Au cours des générations successives certains critères biologiques sont suivis; les variations enregistrées sont discutées.

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Summary Two tropical noctuids, E. insulana and S. littoralis, important pests of the cotton plant, have been reared on an artificial medium that had already allowed culturing 18 noctuid species of the Trifinae, composed as follows: maize semolina 28 g, wheat germ 7 g, Brewers' yeast 7,5 g, ascorbic acid 1 g, benzoic acid 0,3 g, Nipagine 0,25 g, aureomycin chlorhydrate 0,03 g, agar 5 g and H₂O 170 g.With E. insulana, adults were sequestered in groups of 5 to 8 pairs; for S. littoralis in groups or as single couples. The adults were fed with 30% honey-water.The caterpillars of E. insulana were kept individually throughout development; S. littoratis larvae were reared in groups during the first few instars and then individually in stages 5 and 6.With each of the two species two stocks were cultured resulting in 9 and 8 generations of E. insulana, 25 and 19 for S. littoralis. At 25° the mean duration of larval plus pupal development for E. insulana was 27.1 days for males and 26.5 days for females; for S. littoralis 28.0 days and 26.7 days for the respective sexes.Incorporation of a mixture of salts (Wesson's salts) in the diet made a significant improvement in rearing E. insulana: larval development was reduced about 3 days, while the percentage of newborn larvae reaching adulthood increased.With each generation of E. insulana a loss of vigour became apparent: prolongation of the mean larval plus pupal development, reduction in the number of females mated. Considerations of similar work lead to an explanation due to genetic rather than to nutritional factors. No such phenomenon appeared with S. littoralis, where the harsh effect of consanguinity could be avoided; the importance of the size of the starting population, and the ease with which group cultures could be used let us obtain numerous individuals in each generation.

     

Une granulose,nouvelle affection deMamestra oleracea L. [Lepidoptera,Noctuidae]

Résumé Une granulose, maladie nouvelle pourMamestra oleracea L., est décrite. L'agent pathogène se multiplie dans la région nucléaire des cellules adipeuses, hypodermiques et trachéales. Les granules et les virus ont été observés au microscope électronique. L'élevage d'un nombre de générations successives relativement élevé, rendu possible par l'emploi d'un aliment artificiel, est envisagé comme cause d'apparition de maladies à virus.

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Summary Mamestra (Polia) oleracea L., a noctuid of economic importance, shows a susceptibility to a very pathogenic granulosis when it is reared on an artificial medium. The pathogen develops in the nuclear area of fat body, hypoderm and trachea cells. Granules and viruses have been observed in electron microscopy.Bergoldiavirus oleraceae nov. sp. is suggested as a denomination. Rearing of many successive generations, made possible by use of artificial diet, is considered as a possible way of introduction of virus diseases in insects.

     

Essai en culture de choux-fleurs du virus de la polyédrose nucléaire deMamestra brassicae [Lep.: Noctuidae]

Résumé Une préparation expérimentale de virus de la polyédrose nucléaire (VNP) deMamestra brassicae L. a été appliquée dans les conditions de la pratique dans un champ de choux-fleurs pour lutter contre cette noctuelle. La préparation, appelée virusine M.B., est fabriquée à partir de chenilles mortes, après infection en élevage de larves du 5^e stade. La période de traitement a été déterminée selon le vol des papillons, suivi par piégeage sexuel. Six traitements par virus ont été effectués tous les 5 à 8 jours. Les 3 doses expérimentées (resp. 0,6 10¹²/3.10¹² et 1,5 10¹³ polyèdres par ha) ont proportionnellement diminué aussi bien l'effectif de la population larvaire que les dégats à la culture de choux-fleurs.

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Summary An experimental preparation of nuclear polyhedrosis virus (NPV) ofMamestra brassicae L. (named “virusine M.B.”, was applied under routine conditions to a field of cauliflower for control of this noctuid. The preparation was made from a filtrate of dead larvae, after infection of stock culture of 5 th instar larvae. This filtrate, with the addition of inert materials, was made into a powder in an industrial spray-drier. The resulting powder had the following composition: 50% vegetable charcoal, 35% skim milk powder, and 15% dried larval filtrate. It contained 6×10⁹ polyhedra/g. The biological activity of the preparation was evaluated by bioassay against the crude material prepared by acetone precipitation of a sample of the same filtrate. The objective of the field experiment was to determine the dosage of the preparation necessary to use under field conditions on cauliflower in the Rhone valley. The infection of newly hatched larvae was attempted, to take advantage of their susceptibility compared with later instars. The application period was determined by the flight of males into traps baited with virgin females reared in the laboratory. Six applications of virus were made, August 11, 18, and 24 and September 1, 6, and 13, 1977 (every 5 to 8 days). Between August 23 and September 2 a complementary release of 65 pairs ofMamestra was made to ensure a high population density of larvae in the crop. This action was unnecessary because it was demonstrated that the natural infestation was dense enough. Each dosage was applied to 4 plots of 180 m² with an average of 400 plants each. In addition, 2 spraying with Bactospeine (aBacillus thuringiensis preparation) was applied againstPieris brassicae L. on all 4 plots. The results of the treatment with virusine M.B. againstM. brassicae were quite satisfactory with regard to insect mortality and crop protection.