Aphid–Plant–Phytovirus Pathosystems: Influencing Factors from Vector Behaviour to Virus Spread

Aphids are responsible for the spread of more than half of the known phytovirus species. Virus transmission within the plant–aphid–phytovirus pathosystem depends on vector mobility which allows the aphid to reach its host plant and on vector efficiency in terms of ability to transmit phytoviruses. However, several other factors can influence the phytoviruses transmission process and have significant epidemiological consequences. In this review, we aimed to analyse the aphid behaviours and influencing factors affecting phytovirus spread. We discussed the impact of vector host-seeking and dispersal behaviours mostly involved in aphid-born phytovirus spread but also the effect of feeding behaviours and life history traits involved in plant–aphid–phytovirus relationships on vector performances. We also noted that these behaviours are influenced by factors inherent to the interactions between pathosystem components (mode of transmission of phytoviruses, vector efficiency, plant resistance, …) and several biological, biochemical, chemical or physical factors related to the environment of these pathosystem components, most of them being manipulated as means to control vector-borne diseases in the crop fields.

Development on Infected Citrus over Generations Increases Vector Infection by ‘Candidatus Liberibacter Asiaticus in Diaphorina citri’

‘Candidatus Liberibacter asiaticus’ (CLas) is a major causal agent of citrus Huanglongbing (HLB), which is transmitted by Asian citrus psyllid (ACP), Diaphorina citri, causing severe losses in various regions of the world. Vector efficiency is higher when acquisition occurs by ACP immature stages and over longer feeding periods. In this context, our goal was to evaluate the progression of CLas population and infection rate over four ACP generations that continuously developed on infected citrus plants. We showed that the frequency of CLas-positive adult samples increased from 42% in the parental generation to 100% in the fourth generation developing on CLas-infected citrus. The bacterial population in the vector also increased over generations. This information reinforces the importance of HLB management strategies, such as vector control and eradication of diseased citrus trees, to avoid the development of CLas-infected ACP generations with higher bacterial loads and, likely, a higher probability of spreading the pathogen in citrus orchards.

Comparative Vector Efficiency of Two Prevalent Mosquito Species for Dog Heartworm in North Carolina

The dog heartworm, Dirofilaria immitis (Leidy) (Spirurida: Onchocercidae), is a devastating parasite of domestic and wild canines vectored by a multitude of mosquito species. Although many species are implicated as vectors, not all contribute equally to disease transmission, with demonstrated variation in vector efficiency between and within species. We investigated the vector efficiency of mosquitoes derived from wild-caught North Carolina populations of two known heartworm vectors: a native species, Aedes triseriatus (Say) (Diptera: Culicidae), and an invasive species, Aedes albopictus (Skuse). We compared the parasite developmental times within the mosquito, mosquito longevity and fecundity, and the vector efficiency index between the two species. We found that the tested composite North Carolina population of Ae. triseriatus was an efficient vector of D. immitis under laboratory conditions, whereas the local composite population of Ae. albopictus was a competent but relatively poor vector. Compared with Ae. triseriatus, Ae. albopictus showed a longer time for parasite development, lower infection rates, and lower vector efficiency. Additionally, Ae. albopictus was the sole species to exhibit significant parasite-induced mortality. These results are in contrast to prior studies of populations of Ae. albopictus from locations outside of North Carolina, which have implicated the species as a highly competent heartworm vector. The variation seen for different strains of the same species emphasizes the heritable nature of D. immitis vector competence and highlights the need for local infection studies for accurate transmission risk assessment in a particular locale.

Why Evolve Reliance on the Microbiome for Timing of Ontogeny?

ABSTRACT The timing of life history events has important fitness consequences. Since the 1950s, researchers have combined first principles and data to predict the optimal timing of life history transitions. Recently, a striking mystery has emerged. Such transitions can be shaped by a completely different branch of the tree of life: species in the microbiome. Probing these interactions using testable predictions from evolutionary theory could illuminate whether and how host-microbiome integrated life histories can evolve and be maintained. Beyond advancing fundamental science, this research program could yield important applications. In an age of microbiome engineering, understanding the contexts that lead to microbiota signaling shaping ontogeny could offer novel mechanisms for manipulations to increase yield in agriculture by manipulating plant responses to stressful environments, or to reduce pathogen transmission by affecting vector efficiency. We combine theory and evidence to illuminate the essential questions underlying the existence of microbiome-dependent ontogenetic timing (MiDOT) to fuel research on this emerging topic.

Why evolve reliance on the microbiome for timing of ontogeny?

The timing of life history events has important fitness consequences. Since the 1950s, researchers have combined first principles and data to predict the optimal timing of life history transitions. Recently, a striking mystery has emerged. Such transitions can be shaped by a completely different branch of the tree of life: bacterial species in the microbiome. Probing these interactions using testable predictions from evolutionary theory could illuminate whether and how host-microbiome integrated life histories can evolve and be maintained. Beyond advancing fundamental science, this research program could yield important applications. In an age of microbiome engineering, understanding the contexts that lead to microbiota signaling shaping ontogeny could offer novel mechanisms for manipulations to increase yield in agriculture, or reduce pathogen transmission by affecting vector efficiency. We combine theory and evidence to illuminate the essential questions underlying the existence of Microbiome Dependent Ontogenetic Timing (MiDOT) to fuel research on this emerging topic.

Numerical Investigation on a New Concept of Shock Vector Control Nozzle

Shock vector control (SVC) based on transverse jet injection is one of the fluidic thrust vectoring (FTV) technologies, and is considered as a promising candidate for the future exhaust system working at high nozzle pressure ratio (NPR). However, the low vector efficiency (η) of the SVC nozzle remains an important problem. In the paper, a new method, named as the improved SVC, was proposed to improve the vector efficiency (η) of a SVC nozzle, which enhances the vector control of primary supersonic flow by adopting a bypass injection. It needs less secondary flow from high pressure component of an aero-engine and has smaller influence on the working character of an aero-engine. The flow mechanism of the improved SVC nozzle was investigated by solving three-dimensional Reynolds-averaged Navier--Stokes with shear stress transport (SST) κ–ω turbulence model. The shock waves, jets-primary flow interactions, flow separation, and vector performance were analyzed. The influences of aerodynamic and geometric parameters, namely, NPR, secondary pressure ratio (SPR), and bypass injection position (Xj.ad.) on flow characteristics and vector performance were investigated. Based on the design of experiment (DOE), the response surface methodology (RSM) and the simulation model of an aero-engine, a method to estimate the coupling performance of the improved SVC nozzle and an aero-engine was studied, and a new balance relationship between the improved SVC nozzle and an aero-engine was established. Results shows that (1) with the assistance of bypass injection, the jet penetration and the capability of vector control are largely improved, resulting in a vector efficiency (η) of 1.98 deg/%-ω at the designed NPRD = 13.88; (2) in a wide range of operating conditions, larger vector angle (δp), higher thrust coefficient (Cfg), and higher vector efficiency (η) of the improved SVC nozzle were obtained, (3) in the coupling process of the improved SVC nozzle and an aero-engine, a δp of 18.1 deg was achieved at corrected secondary flow ratio of 10% and corrected bypass ratio of 6.98%, and the change of the thrust and the specific fuel consumption (SFC) were within 12%, which is better than the coupling performance of a SVC nozzle and an aero-engine.

Surplus Labour in the Unorganised Sector of India

Disguised unemployment is the wastage of labour resource of a country. For a country like India that wishes to move towards a fast growth tract, disguised unemployment is a serious setback to the growth path. Several theoretical justifications have been provided to contextualize disguised unemployment. They all assume homogeneous production structure across firms. However, the informal sector in India is a conglomeration of different firm types. In India, the NSSO data subdivided firms into family enterprises (Own Account Enterprises – OAE) and commercially motivated (Establishment). The authors require a theoretical justification following this line. In this chapter, they generalise the argument provided by Georgescu-Roegen (1960) for this purpose. In this chapter, an attempt is made to measure surplus labour in the informal sector of India using NSSO data. For this, the concept of sub-vector efficiency as developed by Ray (2005) is used. The authors calculate surplus labour in OAEs and EST firms separately.