How parasitoid sex ratio,size and emergence time are associated with fruit tree cultivar,within-orchard tree position and ants

The biocontrol potential of naturally occurring parasitoids is influenced by the parasitoids’ population and individual characteristics. We studied field determinants of characteristics of the parasitoid Scambus pomorum (Hymenoptera: Ichneumonidae) emerging from weevils (Anthonomus pomorum; Coleoptera: Curculionidae) hidden in damaged apple blossoms. The studied determinants comprised local-scale factors that can be managed by individual growers: tree cultivar, distance between apple trees and forest, and presence of ants. The studied parasitoid characteristics were sex ratio, body size and emergence time. Parasitoid sex ratio, in general female-biased, was significantly different for parasitoids emerging from hosts feeding on different apple cultivars. This finding suggests sex ratio adjustment driven by plant genotype-dependent variation in parasitoid host quality. The detected significant increase of sex ratio (more males) with increasing distance to forest might be explained by sperm depletion of ovipositing parasitoid females immigrating into the orchard. Exclusion of ants significantly increased female-bias in sex ratio in one of the studied apple cultivars. Body size of female and male parasitoids was significantly different between parasitoids emerging from different apple cultivars, supporting the view of cultivar-dependent variation in the quality of the parasitoid’s host. Distance to forest was positively correlated with parasitoid size, indicating farther dispersal of larger individuals. Emergence time varied significantly between apple cultivars, probably due to differences in plant phenology. By demonstrating that parasitoid characteristics vary widely within an orchard, this study shows that parasitoid characteristics that are relevant for biological control might be improved via appropriate management of the orchard and its immediate surroundings.     

Platelet adhesive dynamics. Part I: characterization of platelet hydrodynamic collisions and wall effects

Abnormally high shear stresses encountered in vivo induce spontaneous activation of blood platelets and formation of aggregates, even in the absence of vascular injury. A three-dimensional multiscale computational model—platelet adhesive dynamics—is developed and applied in Part I and Part II articles to elucidate key biophysical aspects of GPIbα-von-Willebrand-factor-mediated interplatelet binding that characterizes the onset of shear-induced platelet aggregation. In this article, the hydrodynamic effects of the oblate spheroidal shape of platelets and proximity of a plane wall on the nature of cell-cell collisions are systematically investigated. Physical quantities characterizing the adhesion probabilities between colliding platelet surfaces for the entire range of near-wall encounters between two platelets are obtained for application in platelet adhesive dynamics simulations of platelet aggregation explored in a companion article. The technique for matching simulation predictions of interplatelet binding efficiency to experimentally determined efficiencies is also described. Platelet collision behavior is found to be strikingly different from that of spheres, both close to and far from a bounding wall. Our results convey the significant effects that particle shape and presence of a bounding wall have on the particle trajectories and collision mechanisms, collision characteristics such as collision time and contact area, and collision frequency.     

GABA(A)R plasticity during pregnancy: relevance to postpartum depression

Fluctuating neurosteroid levels over the ovarian cycle modulate neuronal excitability through effects on GABA(A) receptors (GABA(A)Rs). The large increase in progesterone-derived neurosteroids during pregnancy and their precipitous decline at parturition may have considerable effects on GABA(A)Rs during pregnancy and postpartum. Here we show a significant decrease in tonic and phasic inhibitions in pregnant mice, mediated by a downregulation of GABA(A)R delta and gamma2 subunits, respectively, which rebounds immediately postpartum. Mice which do not exhibit GABA(A)R delta subunit regulation throughout pregnancy (Gabrd(+/-) and Gabrd(-/-)) exhibit depression-like and abnormal maternal behaviors, resulting in reduced pup survival. These abnormal postpartum behaviors were ameliorated in Gabrd(+/-) mice by a GABA(A)R delta-subunit-selective agonist, THIP. We suggest that Gabrd(+/-) and Gabrd(-/-) mice constitute a mouse model of postpartum depression that may be useful for evaluating potential therapeutic interventions.     

Differential susceptibility and suitability of domestic and wild apple species for a florivorous weevil and its parasitoids

Crop plant domestication can change plant resistance to herbivores leading to differences in pest pressure experienced by crop plants and their wild relatives. To compare resistance to herbivores between domesticated and wild fruit trees, we quantified direct resistance and indirect resistance to a pest insect, the florivorous apple blossom weevil Anthonomus pomorum (Coleoptera: Curculionidae), for the cultivated apple Malus domestica and two wild apple species, the European crab apple M. sylvestris and the exotic M. kirghisorum. We measured weevil infestation and performance (weight, sex ratio), and weevil parasitism by parasitoid wasps for different cultivars of M. domestica and for the two wild apple species. To explain weevil and parasitoid responses to different apple species, we quantified tree characteristics including nitrogen content, size of flower buds, bark roughness, tree size, tree phenology and tree position. We found significant differences in susceptibility to weevil infestation between apple species, with lowest infestation (highest apple resistance) in M. domestica and highest infestation in M. kirghisorum. The suitability of apple species also varied significantly: weevils emerging from M. sylvestris were significantly lighter than those from M. kirghisorum. Parasitism of A. pomorum by different parasitoid species was significantly higher in M. sylvestris than in M. domestica. Infestation, weevil weight and parasitism were positively related to tree characteristics: infestation to bud nitrogen content and bark roughness, weevil size to nitrogen content and bud size, and parasitism to tree height and bud density. Our study revealed marked differences between apple species in susceptibility and suitability for the pest herbivore, but also for antagonistic parasitoids. Whereas direct resistance appeared to be higher in cultivated apple, indirect resistance via parasitoids was apparently higher in wild apple trees. Our findings suggest that wild and cultivated apple trees possess different resistance traits that may be combined to optimize resistance in commercial apple cultivars.     

Cleavage of vasoactive intestinal peptide at multiple sites by autoantibodies

Vasoactive intestinal peptide (VIP) fragments generated by autoantibodies purified from the blood of two human beings were separated and sequenced. Based on the identity of these fragments, seven peptide bonds cleaved by the antibodies were identified. Six of the seven scissile bonds are clustered in the region of VIP spanning residues 14-22 and were cleaved by antibodies from both human subjects. The seventh scissile bond is located at residues 7-8 and was cleaved by antibodies from one of the subjects. The scissile bonds link amino acid residues with different size, charge, and hydrophobicity. The hydrolytic activity of the antibodies was selective in that they failed to hydrolyze polypeptides unrelated in sequence to VIP (insulin and atrial natriuretic peptide). These observations demonstrate substrate specific hydrolysis by naturally occurring antibodies and expand the range of peptide bonds hydrolyzed by these antibodies.     

Vasoactive intestinal peptide hydrolysis by antibody light chains

This paper describes evidence for hydrolysis of a neuropeptide, vasoactive intestinal peptide (VIP), by light chains purified from the IgG of a human subject positive for VIP binding antibodies. Purified IgG was digested with papain, resultant fragment antigen binding (Fab) fragments were reduced with 2-mercaptoethanol and alkylated with iodoacetamide, and light chains were purified by chromatography on immobilized antibodies to light chains and immobilized antibodies to heavy chains. Non-immunoglobulin components were undetectable in the light chain preparation, judged by sodium dodecyl sulfate-electrophoresis and Western blotting with anti-heavy and anti-light chain antibodies. The light chains hydrolyzed VIP with specific activity 32-fold greater than that of Fab, the pH optimum for light chain-mediated VIP hydrolysis was 7.0-7.5, and the hydrolytic activity was saturable (Vmax, 0.19 pmol/min/microgram light chains; substrate concentration at Vmax/2,380 nM).     

Influence of far-ultraviolet radiation on the permeability of the outer membrane of Escherichia coli

Far-ultraviolet radiation (254 nm) at a dose of 10, 20, and 30 J/m2 was found to disrupt the outer membrane permeability barrier of Escherichia coli to various antibiotics, dyes, and detergents. The degree of sensitization to these agents was proportional to the radiation dose. The irradiated cells showed a significant increase in the sensitivity of hydrophilic antibiotics (ampicillin, carbenicillin, penicillin), whereas much less sensitization was found towards hydrophobic probes (kanamycin, erythromycin, rifamycin SV, crystal violet, phenol, novobiocin) and detergents (dodecyl sulfate, bile salt, Triton X-100). The biochemical data and ultrastructural analysis of the outer membrane by freeze-etching have shown that the increase in phospholipid:protein ratio after irradiation had changed the architecture of the outer membrane from a highly asymmetric bilayer structure with densely packed lipopolysaccharide--protein particles on the outer half, to one predominantly exhibiting smooth phospholipid bilayer characteristics. The structure, composition, and barrier function of the outer membrane were restored to normal within 3 h of postirradiation incubation in nonproliferative medium. During this period, the acquisition of resistance towards a hydrophilic antibiotic (ampicillin) was faster than that for a hydrophobic agent (phenol).