Pollen Provisioning Enhances the Performance of Amblydromalus limonicus on an Unsuitable Prey

Amblydromalus limonicus is a polyphagous phytoseiid predator used for the biological control of thrips and whiteflies in greenhouse crops. Besides various prey species, A. limonicus can also feed on pollen of different plants. Cattail pollen has been previously shown to be suitable for the development and reproduction of A. limonicus. Hence, it could sustain its populations in periods of prey scarcity. In the present study, we hypothesized that pollen provisioning may benefit A. limonicus in mixed diets with prey of low quality, such as spider mites and thus, positively impact ecosystem services provided by this predator. For this, the performance and predation efficiency of A. limonicus against spider mites was assessed in the presence or absence of pollen. Our results show that pollen significantly shortens the developmental time and increases the survival and oviposition of the predator when mixed with spider mites, although it negatively affects its predation rate. Nevertheless, pollen enhances the maintenance of juvenile predators on the leaf by substantially decreasing their dispersal rate in the mixed diet with spider mites. In addition, the intrinsic rate of population increase (rm) of A. limonicus feeding with spider mites increased with the addition of pollen suggesting an increase in its population. Cattail pollen as supplementary food may thus expand the prey species range that A. limonicus could exploit. It can also enhance ecosystem services provided against other pests (thrips and whiteflies) by positively affecting the increase of A. limonicus population

Novel 2,6-diketopiperazine-derived acetohydroxamic acids as promising anti-Trypanosoma brucei agents.

Aim: Identification of new, effective and selective trypanocidal agents. Materials & methods: Twelve novel acetohydroxamic acid derivatives based on 2-alkyl-2-aryl-2,6-diketopiperazine scaffolds have been synthesized and evaluated in vitro for their growth inhibitory activity against bloodstream form Trypanosoma brucei. Results: All the analogs were remarkably potent inhibitors, with low micromolar to submicromolar activities. Structure-activity relationship studies demonstrated that the presence of an alkyl substituent at the N(4)-position of the 2,6-diketopiperazine ring portion was, in general, beneficial to trypanocidal activity in this series. Conclusion: The highest activity resulted from the introduction of a methyl, n-propyl or n-butyl substituent to the N(4)-position of the parent compound. Importantly, the most potent analogs were found to be highly selective against T. brucei with respect to mammalian cells

Novel Lipophilic Acetohydroxamic Acid Derivatives Based on Conformationally Constrained Spiro Carbocyclic 2,6-Diketopiperazine Scaffolds with Potent Trypanocidal Activity

We describe novel acetohydroxamic acid derivatives with potent activity against cultured bloodstream-form Trypanosoma brucei and selectivity indices of >1000. These analogues were derived from conformationally constrained, lipophilic, spiro carbocyclic 2,6-diketopiperazine (2,6-DKP) scaffolds by attaching acetohydroxamic acid moieties to the imidic nitrogen. Optimal activity was achieved by placing benzyl groups adjacent to the basic nitrogen of the 2,6-DKP core. S-Enantiomer 7d was the most active derivative against T. brucei (IC(50) = 6.8 nM) and T. cruzi (IC(50) = 0.21 μM)

Solvent-mediated Pathways to Gelation and Phase Separation in Suspensions of Grafted Nanoparticles

We explore the role of the solvent medium on the interplay between gelation and phase separation in suspensions of organosilicate planar hybrids grafted with hydrocarbon chains. We establish their phase diagram by means of dynamic light scattering, rheology and visual observations, and different routes to gelation, depending on the solvent used. In agreement with earlier works, the solvent quality for the grafted chains at a given temperature controls the balance between attractions and repulsions, and hence the phase diagram of the nanoparticles and their tendency to gel. Here we show how to tune the suspension state and hence its rheology. For decane, a good solvent for the hydrocarbon chains, gelation occurs at rather low volume fractions in the presence of phase separation. This is due to the interdigitation of solvent molecules with the grafted chains, resulting in their crystalline packing that promotes the attraction between particles. For toluene, a solvent of reduced quality for the hydrocarbon chains, no interdigitation takes place, and hence gelation is triggered by clustering at higher volume fractions before phase separation. Our results support the generic picture of complex kinetic arrest/phase separation interplay in soft matter, where phase separation can proceed, be interrupted or be completely inhibited. A number of interesting possibilities for tailoring the rheology of grafted colloidal systems emerge.We would like to thank B. Mueller and E. Pavlopoulou for the refractive index contrast and the SAXS measurements, respectively, as well as A. Larsen and D. Kendristaki for assistance in some PCS and rheology measurements. We are grateful to B. Loppinet for helpful discussions and to J. K. G. Dhont for insightful comments and for bringing to our attention refs. 38 and 73. This work was supported in part by the EU NoE-Softcomp(NMP3-CT-2004-502235). EPG acknowledges the support of Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST)

Elongational Rheology and Brillouin Light Scattering of Entangled Telechelic Polybutadiene Based Temporary Networks

This article focuses on the characterization of a series of telechelic polybutadienes with acid end groups (PBd-COOH) neutralized with different alkali metal ions by elongational rheometry. Depending on the ion, the material is found to be strain-hardening or not. While the Li+ ions cause a strain hardening similar to that observed for low density polyethylene. Na+ and K+ essentially do not lead to any strain hardening. Rb+ leads to a different type of strain hardening, like sparsely branched polymers. It is also found that the material behaves brittlely at strain rates epsilon higher than the crossover frequency omega(c). Additionally, an esterified version of the material and the rubidium hydroxide neutralized PBd-COOH is characterized by Brillouin light scattering to assess the local chain dynamics, being essentially noninfluenced by the ion clusters. The dependence of the longitudinal sound velocity c(i) and hence the longitudinal modulus M from the phonon wave vector q and from the temperature T is compared for two different samples (with and without counterion). It is found that M is insensitive to the presence of the ionic clusters, and therefore, the local chain dynamics are essentially the same for the two model systems and do not play a role in the strain-hardening