Réflexion sur l'utilisation des auxiliaires entomophages contreDiprion pini [Hym. Diprionidae]

Résumé Le problème de la lutte biologique en forêt, par utilisation d'entomophages indigènes, est discuté dans le cas d'un hyménoptère, le diprion du pin,Diprion pini L. Des études de dynamique des populations montrent que le schéma de progression spatiale des populations de cet insecte dans le sud du Bassin Parisien semble se renouveler à chaque pullulation. De plus les parasites représentent un véritable “facteur clé”. Leur incidence varie notamment de génération en génération: en faible nombre au début d'une gradation, ils ne peuvent alors en empêcher le développement; mais ensuite leur multiplication assure une régression brutale du ravageur. Dans ces conditions, des interventions assez peu onéreuses et faciles à réaliser, comme de simples transports de matériel parasité pourraient être efficaces; elles supposent toutefois le développement d'un foyer initial d'infestation. En revanche l'élevage d'espèces régulatrices commeAchrysocharella ruforum Krausse etPleolophus basizonus Grav. permettrait d'assurer la préservation permanente des massifs forestiers.

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Summary The spatial pattern of insect populations progression in southern “Bassin Parisien”, showed by population dynamics studies, seems to happen again for every outbreak. Parasites are moreover a true “key-factor”. Their effect is quite different from one generation to another one; scarce at the beginning of an outbreak, they cannot stop its evolution; but then, their increase allows a brutal collape of the pest. In such a case, cheap and easily achieved operations as simple carryings of parasited insects may be efficient, but they need the development of a first infestation focus. In return breeding of regulating species asAchrysocharella ruforum Krausse andPleolophus basizonus Grav. would be able to sure forest stands permanently.

     

Diversity in the immune system: “Preconceived ideas” or ideas preconceived?

Two concepts of the evolution and regulation of expression of the combining site repertoire of the immune system, are compared. One view is based on the Associative Recognition Theory as formulated by the author and the other is based on the Idiotype Network Idea as conceived by Jerne. The two concepts are analyzed from the point of view of their logic, internal consistency and factual support.     

Sequence analysis of a Dictyostelium discoideum gene coding for an active dihydroorotate dehydrogenase in yeast

A Dictyostelium discoideum DNA fragment isolated on the basis of its ability to complement the ural mutation of yeast, codes for a dihydroorotate dehydrogenase activity. The complete nucleotide sequence of this 1898 bp fragment has been determined and reveals an open reading frame capable of coding for a 369 amino acid polypeptide of molecular mass 47.000. The gene shows preferential use of codons with weak pairing forces. Eleven codons, mainly those with a G in the third position, are absent. The flanking sequences are unusually rich in A + T (80%). Several direct and inverted repeats exist in the 5' flanking sequence.     

CONSÉQUENCE DE LA VARIATION DES EFFECTIFS DES FEMELLES DE DINARMUS VAGABUNDUS,SUR LE PARASITISME DE L'UN DE LEURS HÔTES CALLOSOBRUCHUS MACULATUS

Lorsque 2 femelles ou 3 femelles de l'ectoparasite D. vagabundus parasitent conjointement un même lot d'hôtes l'intensité du grégarisme larvaire s'accroît par rapport à celui observé en présence d'une seule femelle pondeuse. Cela se traduit par une augmentation significative du nombre moyen de descendants des 2 sexes mais la production moyenne en fils est toujours très inférieure à celle des filles. Cependant, lorsque la densité de femelles pondeuses passe de 1 à 3, le rapport des sexes mâles/femelles des descendants évolue vers l'unité traduisant une augmentation plus rapide de l'effectif des fils que des filles.     

Protective effects of differentiation inducers on natural killer sensitivity of K 562 cells: Analysis at a single-cell level

K 562 cells induced to differentiate by sodium butyrate (SB) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were studied for their capacities to be bound and killed by large granular lymphocytes (LGL) in a single-cell cytotoxicity assay in agarose. After SB treatment, K 562 cells were less efficient in binding to LGL, whereas the frequency of killer cells among bound LGL was unaffected. When TPA was used to induce K 562 differentiation, the binding of LGL to their target and the lytic efficiency of the bound LGL were both diminished when compared to control K 562 cells. It has been demonstrated that the expression of structures involved in the binding of natural killer (NK) effectors to their targets could be correlated with the target-differentiation stage. It is shown that phorbol-ester treatment can also affect NK target structures involved in the killing step.