Effect of temperature and parasite density on three species ofAphytis (Hymenoptera: Aphelinidae), parasitising California red scale

Summary Three species ofAphytis parasites of California red scale,Aonidiella aurantii (Maskell) were each confined at different densities with approximately equal numbers of scale insects at several constant temperatures to determine the effect of these factors on progeny production and distribution and the search rate. Egg location on the host body by the parasites was unaffected by temperature or parasite density.A. melinus laid its eggs both dorsally and ventrally in equal proportions whileA. lingnanensis andA. chrysomphali laid their eggs ventrally. Progeny production byA. melinus andA. lingnanensis increased at the higher temperature; that ofA. chrysomphali did not. Unlike the other species,A. chrysomphali failed to oviposit at 32°C. Although increasing parasite density reduced progeny production in bothA. melinus andA. lingnanensis, they were able to maintain an almonst constant search rate. This was due to their ability to distribute their eggs among the hosts more regularly at the higher parasite densities. While the mechanism of this process is easy to understand forA. melinus which behaved as a gregarious parasite, it is unclear forA. lingnanensis, which is almost a solitary parasite. The progeny production and the search rate ofA. chrysomphali dropped significantly with increasing parasite density.     

Functional response to host density by the egg parasiteTrichogramma pretiosum

The effect of host density on parasitism byTrichogramma pretiosum Riley was studied by exposing groups of 150, 300, 600 or 1200 eggs of potato tuber moth to 2, 4 or 8 female parasites per group. The parasite exhibited a type 2 functional response. As host density increasedT. pretiosum parasitised more hosts, but at a decreasing rate. The attack coefficient (a′) decreased as parasite density increased, whereas the handling time (T _h ) remained almost constant. The search rate (a) decreased with increasing host density.T. pretiosum responded to increasing host density by increasing the number of its encounters with hosts and the number of hosts it parasitised only up to host density of 300 when the parasite density was 2 and up to host density of 600 when the parasite densities were greater and then remained almost constant. The observed incidence of parasitism was higher than that expected on the assumption that the parasites behaved the same at higher host densities as at the lowest. When parasite density was raised from 2 to 8 females per group the percentage of female progeny fell from about 73 to about 48%. A 2-fold increase in the number of female progeny was observed when parasite density was reduced from 8 to 2 and also when the host density was raised from 150 to 1200 eggs.     

Hyphal growth ofHypomyces chlorinus Tul.: An autoradiographic study

Summary The incorporation of the chitin precursor N-acetyl-D-(1-³H) glucosamine byH. chlorinus has been studied by light and electron microscopic autoradiography. Light microscopic autoradiography showed that the incorporation occured preferentially at the hyphal apex. Autoradiograms from electron microscopy were quantitatively evaluated to determine the relative radioactivity incorporation between the cell wall and cytoplasm: this showed that (³H) incorporation took place mainly in the plasmalemma-wall complex. However a small amount of N-acetyl glucosamine can enter into the cytoplasmic space and is then transported by endomembranes (Golgi apparatus-vesicles) to the plasmalemma-cell wall interface before polymerization.Abbreviations PATAg Periodic acid-thiocarbohydrazide-silver proteinate - PTA phosphotungstic acid     

The thelytokous Trichogramma chilonis in Taiwan

Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) with a mode of reproduction different from arrhenotoky was discovered and maintained in the laboratory. With or without mating, individuals of this form were able to produce males, females, and mosaics which varied in morphological characters. Reciprocal and backcrosses between males and females from this form and the arrhenotokous population revealed that they were compatible in mating. Progeny obtained from F1 and F2 proved the existence of gene flow between these two forms which are morphologically indistinguishable. More males were produced as temperature rose to above 25°C, or when females fed on a mixture of tetracycline-hydrochloride and honey (1 mg/1 ml). The impact of parasitoids with such mode of reproduction on biological control is discussed.     

Parasites of the spotted stalk borer,Chilo partellus [Lepidoptera: Pyralidae] in South Africa

One egg parasite, 7 larval parasites, 2 pupal parasites and 3 larval hyperparasites were recorded parasitizing the spotted stalk borer,Chilo partellus (Swinhoe) on maize and grain sorghum in South Africa.Trichogrammatoidea lutea Girault [Trichogrammatidae] parasitized eggs ofC. partellus mainly in mid-summer. The larval parasites were active throughout the season with occasional peaks of up to 75% parasitism.Apanteles sesamiae Cameron [Braconidae], proved to be the most abundant larval parasite. It was recorded fromca. 93% of parasitized larvae but its efficiency was reduced by the hyperparasite,Aphanogmus fijiensis (Ferriére) [Ceraphronidae], which reached sometimes up to 100% parasitism on cocoons ofA. sesamiae. The efficiency ofIphiaulax sp. [Braconidae], the 2^nd most abundant larval parasite, was also hindered by the hyperparasite,Eurytoma sp. [Eurytomidae] Pupal parasites were sometimes very abundant reaching up to 100% parasitism without any interference by hyperparasites. The most abundant pupal parasites wereDentichasmias busseolae Heinrich [Ichneumonidae] andPediobius furvus (Gahan) [Eulophidae].      

Imaging analysis of collagen fiber networks in cusps of porcine aortic valves: effect of their local distribution and alignment on valve functionality

The cusps of native aortic valve (AV) are composed of collagen bundles embedded in soft tissue, creating a heterogenic tissue with asymmetric alignment in each cusp. This study compares native collagen fiber networks (CFNs) with a goal to better understand their influence on stress distribution and valve kinematics. Images of CFNs from five porcine tricuspid AVs are analyzed and fluid-structure interaction models are generated based on them. Although the valves had similar overall kinematics, the CFNs had distinctive influence on local mechanics. The regions with dilute CFN are more prone to damage since they are subjected to higher stress magnitudes.     

Design and Performance of a Multipurpose 2-D Photonic Crystal Device Based on Y Couplers

Plasmonics - This paper reports on the design of a multipurpose photonic device based on 2-D photonic crystals which uses Y couplers in its structure that is very efficient when employed as a...     

Improving the performance of nadolol stereoisomers' preparative separation using Chiralpak IA by SMB chromatography

The pseudobinary preparative separation of nadolol stereoisomers is performed by simulated moving bed chromatography (SMB). Using the Chiralpak IA adsorbent, a new 25:75:0.1 (v/v/v) methanol‐acetonitrile‐diethylamine solvent composition was selected to perform the experimental SMB separation and compare it with the previous results obtained using pure methanol. Using a 2 g L^?1 total feed concentration of an equimolar mixture of the four stereoisomers of nadolol, the more retained component was fully recovered (100% purity and 100% recovery), with a system productivity of 0.77 g L^?1 hour^?1 and a solvent consumption of 9.62 L g^?1. Comparing these results with the ones previously reported using 100:0.1 methanol‐diethylamine solvent composition, this work shows that the 25:75:0.1 methanol‐acetonitrile‐diethylamine is a better alternative for the preparative separation of nadolol stereoisomers by SMB chromatography. These results are confirmed by simulation of the SMB operation for higher feed concentrations, by comparing the performances of the two solvent compositions using the data obtained experimentally through the measurement of the adsorption equilibrium isotherms and the kinetic data obtained for both solvents. The new experimental and simulation results stress out that the performance of the preparative separation can be improved by a careful selection of the solvent composition.