Response of immunocompetent and immunosuppressed Spodoptera littoralis larvae to baculovirus infection.

The Mediterranean lepidopteran pest Spodoptera littoralis is highly resistant to infection with the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) via the oral route, but highly sensitive to infection with budded virus (BV) via the intrahaemocoelic route. To study the fate of AcMNPV infection in S. littoralis, vHSGFP, an AcMNPV recombinant that expresses the reporter green fluorescent protein gene under the control of the Drosophila heat-shock promoter, and high-resolution fluorescence microscopy were utilized. S. littoralis fourth-instar larvae infected orally with vHSGFP showed melanization and encapsulation of virus-infected tracheoblast cells serving the midgut columnar cells. At 72 h post-infection, the viral foci were removed during the moult clearing the infection. Thus, oral infection was restricted by immune responses to the midgut and midgut-associated tracheal cells. By contrast, injection of BV into the haemocoel resulted in successful infection of tracheoblasts, followed by spread of the virus through the tracheal epidermis to other tissues. However, in contrast to fully permissive infections where tracheoblasts and haemocytes are equally susceptible to infection, a severe limitation to vHSGFP infection of haemocytes was observed. To investigate the resistance of S. littoralis haemocytes to BV infection with AcMNPV, the larval immune system was suppressed with the Chelonus inanitus polydnavirus or a putatively immunosuppressive polydnavirus gene, P-vank-1. Both treatments increased the susceptibility of S. littoralis larvae to AcMNPV. It is concluded that the resistance of S. littoralis to AcMNPV infection involves both humoral and cellular immune responses that act at the gut and haemocyte levels. The results also support the hypothesis that tracheolar cells mediate establishment of systemic baculovirus infections in lepidopteran larvae. The finding that polydnaviruses and their encoded genes synergize baculovirus infection also provides an approach to dissecting the responses of the lepidopteran immune system to viruses by using specific polydnavirus immunosuppressive genes.

Reference-wave solution for the two-frequency propagator in a statistically homogeneous random medium.

Spatial and temporal structures of ultrawide-band high-frequency fields can be appreciably affected by random changes of the medium parameters characteristic of almost all geophysical environments. The dispersive properties of random media cause distortions in the propagating signal, particularly in pulse broadening and time delay. Theoretical analysis of pulsed signal propagation is usually based on spectral decomposition of the time-dependent signal and the analysis of the two-frequency mutual coherence function. In this work we present a new reference-wave method and apply it to solving the equation of the two-frequency mutual coherence function propagator. This method is based on embedding the problem into a higher-dimensional space and is accompanied by the introduction of additional coordinates. Choosing a proper transform of the extended coordinate system allows us to emphasize "fast" and "slow" varying coordinates which are consequently normalized to the scales specific to a given type of problem. Such scaling usually reveals the important expansion parameter defined as a ratio of the characteristic scales and allows us to present the equation being solved as a hierarchy of terms having a decreasing order of expansion with respect to this parameter. We present an analytical result for the two-frequency mutual coherence function propagating in a random medium with arbitrary refractive index fluctuations and show that when approximating the transverse structure function of the medium by a quadratic form, the solution reduces to the exact result derived previously. Extension of the reference-wave method to the analysis of the pulse distortion effects is considered.

Reference-wave solutions for the high-frequency field in random media.

Ray trajectories, as has been shown in the recently formulated stochastic geometrical theory of diffraction, play an important role in determining the propagation properties of high-frequency wave fields and their statistical measures in complicated random environments. The field at the observer can be presented as the superposition of a variety of field species arriving at the observer along multiple ray trajectories resulting from boundaries and scattering centers embedded into the random medium. In such situations the intensity products from which the average intensity measures can be constructed and which, in general, are presented as even products of the total field, will contain sums of products of mixed field species arriving along different ray trajectories. For computations of the statistical measures of the field it is desirable, therefore, to possess a solution for the high-frequency field propagating along an isolated ray trajectory. The main concern of this work is the construction of high-frequency asymptotic propagators, relating the values of the random field and its statistical measures at some observation plane to their source (actual or virtual) distributions at the initial plane. For this reason a reference-wave method was developed to obtain an approximate solution of the parabolic wave equation in a homogeneous background random medium.

Reference-wave solutions for high-frequency fields propagating in random media.

Ray theory plays an important role in determining the propagation properties of high-frequency fields and their statistical measures in complicated random environments. According to the ray approach, the field at the observer can be synthesized from a variety of field species arriving along multiple ray trajectories resulting from refraction and scattering from boundaries and from scattering centers embedded in the random medium. For computations of the statistical measures, it is desirable therefore to possess a solution for the high-frequency field propagating along an isolated ray trajectory. For this reason, a new reference-wave method was developed to provide an analytic solution of the parabolic-wave equation.