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Porcine LH receptor ectodomain was overexpressed in insect cells and lepidopteran larvae using the recombinant baculovirus expression system. A low multiplicity of infection yielded the largest active production, of approximately 107 receptors/cell or 3 μg active receptor/mg total protein in infected cells. The truncated ectodomain solubilized with Triton X-100 bound its ligand with a high affinity which was comparable with that of the native membrane receptor. Increasing the multiplicity of infection resulted in an optimum protein production of 0·6 mg receptor/mg total protein in infected cells. This receptor was largely inactive, probably trapped within aggregation pools. Active receptor could be recovered by dilution of the samples. No secretion of recombinant receptor was ever observed whatever the conditions of infection. Expression of the recombinant receptor in insect larvae was also tested. This low-cost system failed both to increase the amount of active receptor and to induce secretion into the haemolymph. Two methods remain for producing sizeable amounts of active receptor with this baculovirus/insect cell system. One relies on immunoaffinity purification of the active protein and requires large-scale production, and the other is based on the purification of overexpressed inactive receptor followed by renaturation.

Overexpression of the porcine LH receptor (pLHR) ectodomain has been achieved using the baculovirusinsect cell system but mostly in an aggregated form with no secretion. In order to carry this out, new baculoviruses were selected to produce the pLHR ectodomain in insect Sf9 cells and caterpillars. In pLHR-P10–297 and pLHR-mel-319 baculoviruses, pLHR cDNA was under the control of the P10 promoter and the polyhedrin gene promoter respectively. The constructs contained either the porcine signal peptide (pLHR-P10–297) or the insect signal peptide of melittin (pLHR-mol-319). Infected cells produced 1 × 105−3 × 105 receptors/cell 3 days after infection. The recombinant LH receptor ectodomains produced were secreted in a biologically active form and bound the hormone with high affinity. Infected caterpillars produced a larger amount of active pLHR ectodomain than insect cells. The products were not secreted into the haemolymph however. Promoter and/or signal peptide modifications therefore enabled pLHR recombinant ectodomain secretion in a biologically active form, using the baculovirus—lepidopteran cell system. Moreover, moderate levels of expression seem to allow the production of biologically active ectodomain.

ChezLymantria dispar L. il est demontre que la plus grande resistance d'un state larvaire par rapport au precedent ne s'explique pas par la difference de poids ou de consommation des chenilles, parce que le poids des chenilles et leur consommation de la surface traitee sont proportionnels.

Par contamination superficielle du milieu artificiel d'elevage, l'activite des virus a polyedres nucleaires d'Autographa californica Speyer (multiplie surSpodoptera exigua Hb.), deMamestra brassicae L. et deScotia segetum Schiff. a ete etudiee a l'aide de poudres preparees d'une facon identique, a l'egard des chenilles neonates deM. brassicae, deS. segetum, deTrichoplusia ni Hb. et deS. exigua. Les trois virus sont pathogenes pour les quatre especes de Noctuelles, mais a des degres differents, que nous proposons d'estimer en «indices de difference de specificite». Dans les cas consideres, ceux-ci varient de 1,5 a 1 000. Les polyedres deA. californica sont les plus actifs pourS. exigua etT. ni, tandis que pourM. brassicae etS. segetum la mortalite la plus importante aux doses les plus faibles est obtenue avec les virus originaires de ces deux especes. Il est souligne l'importance pour la lutte virologique de l'etablissement de spectres d'activite quantitatifs afin de choisir le germe le plus virulent pour toute la serie de recherches et mises au point necessaires avant de parvenir a une formulation applicable dans la pratique.

L'evolution du Baculovirus deMamestra brassicae origine France a ete suivie au cours de passages successifs sur des chenilles du chou infecteesper os au stade L5. Le genome viral d'un poids moleculaire de 148 kpb comporte en debut d'experience 82 sites de restriction reconnus par 7 endonucleases. 81 sites sont conserves au cours des passages repetes. Un site separant les fragmentsHin dIII G etHin dIII J disparait progressivement des populations virales par deletion d'un fragment d'ADN de 2,7 kpb localise entre les positions 0,25 et 0,37 sur la carte de restriction deWiegers & Vlak (1984). Cette modification du genome n'a pas de consequence appreciable sur la virulence des preparations virales successives dont les DL50 pour les larves L1 PM passent de 11 a 17,9 polyedres par mm2 d'aliment contamine en 25 multiplications.