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Papers by Herman Van Mellaert

Research paper thumbnail of Molecular modifications of benzylphenol and benzyl-1,3-benzodioxole types of insect chemosterilants

Pesticide Science, 1986

Rationally planned structural modifications were carried out on benzylphenols and benzyl-1,3-benz... more Rationally planned structural modifications were carried out on benzylphenols and benzyl-1,3-benzodioxoles described as fly chemosterilants and as anti-juvenile hormones. The introduction of a prop-2-ynyloxy group at various sites of the molecule resulted in compounds with a moderate inhibitory action on cytochrome P-450 mono-oxygenases, as measured by aldrin epoxidation. One compound, 5-(4-methoxybenzyl)-6-prop-2-ynyloxy-1,3-benzodioxole, revealed chemosterilant activity on Phormia regina, but its activity was less than that of the parent compounds. 2,4-Di-tert-butyl-6-[4-(3-methoxy-3-methylbutoxy)benzyl]phenol, which possessed a juvenoid structure, revealed no juvenile hormone (JH) activity but showed a high sterilant effect against Dysdercus cingulatus. In contrast to the parent substances, none of the tested compounds showed a detectable anti-JH effect in the Galleria assay. 8-Methoxy-2,3-methylenedioxydibenz[b,e]oxepine, a hitherto undescribed fused heterocyclic ring system, was devoid of activity, indicating the importance of free rotation and/or molecular flexibility. In spite of the moderate activities of these compounds, the manifold biological potential of the quinone-methide mechanism justifies further research on these lines.

Research paper thumbnail of Feeding behavior and growth of Heliothis virescens larvae on diets containing Bacillus thuringiensis formulations or endotoxins

Entomologia Experimentalis Et Applicata, 1991

ABSTRACT

Research paper thumbnail of Mechanism of insect resistance to the microbial insecticide Bacillus thuringiensis

Science, 1990

Receptor binding studies show that resistance of a laboratory-selected Plodia interpunctella stra... more Receptor binding studies show that resistance of a laboratory-selected Plodia interpunctella strain to a Bacillus thuringiensis insecticidal crystal protein (ICP) is correlated with a 50-fold reduction in affinity of the membrane receptor for this protein. The strain is sensitive to a second type of ICP that apparently recognizes a different receptor. Understanding the mechanism of resistance will provide strategies to prevent or delay resistance and hence prolong the usefulness of B. thuringiensis ICPs as environmentally safe insecticides.

Research paper thumbnail of Specificity of Bacillus thuringiensis delta -endotoxins is Correlated with the Presence of High-Affinity Binding Sites in the Brush Border Membrane of Target Insect Midguts

Proceedings of The National Academy of Sciences, 1988

Binding studies were performed with two '251-labeled Bacillus thuringiensis -endotoxins on brush ... more Binding studies were performed with two '251-labeled Bacillus thuringiensis -endotoxins on brush border membrane vesicles prepared from the larval midgut of the tobacco hornworm Manduca sexta or the cabbage butterfly Pieris brassicae. One S-endotoxin, Bt2-protoxin, is a 130-kDa recombinant crystalline protein from B. thuringiensis subsp. berliner. It kills larvae of both insect species. The active Bt2toxin is a 60-kDa proteolytic fragment of the Bt2-protoxin. It binds saturably and with high affinity to brush border membrane vesicles from the midgut of both species. The other

Research paper thumbnail of Effects of Bacillus thuringiensis delta-endotoxin on the permeability of brush border membrane vesicles from tobacco hornworm (Manduca sexta) midgut

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1990

1. The effect of two recombinant Bacillus thuringiensis delta-endotoxins on brush border membrane... more 1. The effect of two recombinant Bacillus thuringiensis delta-endotoxins on brush border membrane vesicles of Manduca sexta midgut was investigated using an in vitro assay system, based on ion-amino acid cotransport.2. A CryIA(b)-toxin provoked an increase in the permeability of the vesicles.3. A CryIB-toxin, not toxic to M. sexta larvae in vivo, had no effect in our assay.4. In contrast to earlier reports, the increase in permeability was found to be neither selective for K+ nor specifically inhibited by Ca2+ or Ba2+.5. Our data support the hypothesis that B. thuringiensis delta-endotoxins create non-specific pores.

Research paper thumbnail of Polyploidization and localisation of poly(A) + RNA in the different cell types of the vitellogenic meroistic ovary of the fleshfly, Sarcophaga bullata

Histochemistry and Cell Biology, 1986

The degree of polyploidization, the level of transcriptional activity and the volume of the diffe... more The degree of polyploidization, the level of transcriptional activity and the volume of the different cell types present in the meroistic ovary of Sarcophaga bullata were measured during different vitellogenic stages. The nurse cells and the germinal vesicle exhibited very pronounced differences with regard to DNA content and mRNA synthesis, even though they are genetically identical. During the 4C stage (late vitellogenesis), we observed different degrees of polyploidy in follicle cells adjacent to the oocyte and those surrounding the nurse cells. Although the chromatin of the germinal vesicle is condensed into a karyosome, in situ hybridisation revealed the presence of transcriptional activity. The volume of the germinal vesicle, which contains only 4C DNA, is big enough to contain 2048C DNA. The meroistic ovary is a highly polarized differentiating system. Our results are discussed in the light of the fact that the polytrophic ovary is a miniature electrophoresis chamber.

Research paper thumbnail of Molecular modifications of benzylphenol and benzyl-1,3-benzodioxole types of insect chemosterilants

Pesticide Science, 1986

Rationally planned structural modifications were carried out on benzylphenols and benzyl-1,3-benz... more Rationally planned structural modifications were carried out on benzylphenols and benzyl-1,3-benzodioxoles described as fly chemosterilants and as anti-juvenile hormones. The introduction of a prop-2-ynyloxy group at various sites of the molecule resulted in compounds with a moderate inhibitory action on cytochrome P-450 mono-oxygenases, as measured by aldrin epoxidation. One compound, 5-(4-methoxybenzyl)-6-prop-2-ynyloxy-1,3-benzodioxole, revealed chemosterilant activity on Phormia regina, but its activity was less than that of the parent compounds. 2,4-Di-tert-butyl-6-[4-(3-methoxy-3-methylbutoxy)benzyl]phenol, which possessed a juvenoid structure, revealed no juvenile hormone (JH) activity but showed a high sterilant effect against Dysdercus cingulatus. In contrast to the parent substances, none of the tested compounds showed a detectable anti-JH effect in the Galleria assay. 8-Methoxy-2,3-methylenedioxydibenz[b,e]oxepine, a hitherto undescribed fused heterocyclic ring system, was devoid of activity, indicating the importance of free rotation and/or molecular flexibility. In spite of the moderate activities of these compounds, the manifold biological potential of the quinone-methide mechanism justifies further research on these lines.

Research paper thumbnail of Feeding behavior and growth of Heliothis virescens larvae on diets containing Bacillus thuringiensis formulations or endotoxins

Entomologia Experimentalis Et Applicata, 1991

ABSTRACT

Research paper thumbnail of Mechanism of insect resistance to the microbial insecticide Bacillus thuringiensis

Science, 1990

Receptor binding studies show that resistance of a laboratory-selected Plodia interpunctella stra... more Receptor binding studies show that resistance of a laboratory-selected Plodia interpunctella strain to a Bacillus thuringiensis insecticidal crystal protein (ICP) is correlated with a 50-fold reduction in affinity of the membrane receptor for this protein. The strain is sensitive to a second type of ICP that apparently recognizes a different receptor. Understanding the mechanism of resistance will provide strategies to prevent or delay resistance and hence prolong the usefulness of B. thuringiensis ICPs as environmentally safe insecticides.

Research paper thumbnail of Specificity of Bacillus thuringiensis delta -endotoxins is Correlated with the Presence of High-Affinity Binding Sites in the Brush Border Membrane of Target Insect Midguts

Proceedings of The National Academy of Sciences, 1988

Binding studies were performed with two '251-labeled Bacillus thuringiensis -endotoxins on brush ... more Binding studies were performed with two '251-labeled Bacillus thuringiensis -endotoxins on brush border membrane vesicles prepared from the larval midgut of the tobacco hornworm Manduca sexta or the cabbage butterfly Pieris brassicae. One S-endotoxin, Bt2-protoxin, is a 130-kDa recombinant crystalline protein from B. thuringiensis subsp. berliner. It kills larvae of both insect species. The active Bt2toxin is a 60-kDa proteolytic fragment of the Bt2-protoxin. It binds saturably and with high affinity to brush border membrane vesicles from the midgut of both species. The other

Research paper thumbnail of Effects of Bacillus thuringiensis delta-endotoxin on the permeability of brush border membrane vesicles from tobacco hornworm (Manduca sexta) midgut

Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 1990

1. The effect of two recombinant Bacillus thuringiensis delta-endotoxins on brush border membrane... more 1. The effect of two recombinant Bacillus thuringiensis delta-endotoxins on brush border membrane vesicles of Manduca sexta midgut was investigated using an in vitro assay system, based on ion-amino acid cotransport.2. A CryIA(b)-toxin provoked an increase in the permeability of the vesicles.3. A CryIB-toxin, not toxic to M. sexta larvae in vivo, had no effect in our assay.4. In contrast to earlier reports, the increase in permeability was found to be neither selective for K+ nor specifically inhibited by Ca2+ or Ba2+.5. Our data support the hypothesis that B. thuringiensis delta-endotoxins create non-specific pores.

Research paper thumbnail of Polyploidization and localisation of poly(A) + RNA in the different cell types of the vitellogenic meroistic ovary of the fleshfly, Sarcophaga bullata

Histochemistry and Cell Biology, 1986

The degree of polyploidization, the level of transcriptional activity and the volume of the diffe... more The degree of polyploidization, the level of transcriptional activity and the volume of the different cell types present in the meroistic ovary of Sarcophaga bullata were measured during different vitellogenic stages. The nurse cells and the germinal vesicle exhibited very pronounced differences with regard to DNA content and mRNA synthesis, even though they are genetically identical. During the 4C stage (late vitellogenesis), we observed different degrees of polyploidy in follicle cells adjacent to the oocyte and those surrounding the nurse cells. Although the chromatin of the germinal vesicle is condensed into a karyosome, in situ hybridisation revealed the presence of transcriptional activity. The volume of the germinal vesicle, which contains only 4C DNA, is big enough to contain 2048C DNA. The meroistic ovary is a highly polarized differentiating system. Our results are discussed in the light of the fact that the polytrophic ovary is a miniature electrophoresis chamber.