Defining virus-carrier networks that shape the composition of the mosquito core virome of a local ecosystem.

Mosquitoes are the most important vectors of emerging infectious diseases. During the past decade, our understanding of the diversity of viruses they carry has greatly expanded. Most of these viruses are considered mosquito-specific, but there is increasing evidence that these viruses may affect the vector competence of mosquitoes. Metagenomics approaches have focused on specific mosquito species for the identification of what is called the core virome. Despite the fact that, in most ecosystems, multiple species may participate in virus emergence and circulation, there is a lack of understanding of the virus-carrier/host network for both vector-borne and mosquito-specific viruses. Here, we studied the core virome of mosquitoes in a diverse local ecosystem that had 24 different mosquito species. The analysis of the viromes of these 24 mosquito species resulted in the identification of 34 viruses, which included 15 novel viruses, as determined according to the species demarcation criteria of the respective virus families. Most of the mosquito species had never been analysed previously, and a comparison of the individual viromes of the 24 mosquito species revealed novel relationships among mosquito species and virus families. Groups of related viruses and mosquito species from multiple genera formed a complex web in the local ecosystem. Furthermore, analyses of the virome of mixed-species pools of mosquitoes from representative traps of the local ecosystem showed almost complete overlap with the individual-species viromes identified in the study. Quantitative analysis of viruses' relative abundance revealed a linear relationship to the abundance of the respective carrier/host mosquito species, supporting the theory of a stable core virome in the most abundant species of the local ecosystem. Finally, our study highlights the importance of using a holistic approach to investigating mosquito viromes relationships in rich and diverse ecosystems.

Dissecting the Species-Specific Virome in Culicoides of Thrace.

Biting midges (Culicoides) are vectors of arboviruses of both veterinary and medical importance. The surge of emerging and reemerging vector-borne diseases and their expansion in geographical areas affected by climate change has increased the importance of understanding their capacity to contribute to novel and emerging infectious diseases. The study of Culicoides virome is the first step in the assessment of this potential. In this study, we analyzed the RNA virome of 10 Culicoides species within the geographical area of Thrace in the southeastern part of Europe, a crossing point between Asia and Europe and important path of various arboviruses, utilizing the Ion Torrent next-generation sequencing (NGS) platform and a custom bioinformatics pipeline based on TRINITY assembler and alignment algorithms. The analysis of the RNA virome of 10 Culicoides species resulted in the identification of the genomic signatures of 14 novel RNA viruses, including three fully assembled viruses and four segmented viruses with at least one segment fully assembled, most of which were significantly divergent from previously identified related viruses from the Solemoviridae, Phasmaviridae, Phenuiviridae, Reoviridae, Chuviridae, Partitiviridae, Orthomyxoviridae, Rhabdoviridae, and Flaviviridae families. Each Culicoides species carried a species-specific set of viruses, some of which are related to viruses from other insect vectors in the same area, contributing to the idea of a virus-carrier web within the ecosystem. The identified viruses not only expand our current knowledge on the virome of Culicoides but also set the basis of the genetic diversity of such viruses in the area of southeastern Europe. Furthermore, our study highlights that such metagenomic approaches should include as many species as possible of the local virus-carrier web that interact and share the virome of a geographical area.

Egg distributions of insect parasitoids: modelling and analysis of temporal data with host density dependence.

A simple numerical procedure is presented for the problem of estimating the parameters of models for the distribution of eggs oviposited in a host. The modelling is extended to incorporate both host density and time dependence to produce a remarkably parsimonious structure with only seven parameters to describe a data set of over 3,000 observations. This is further refined using a mixed model to accommodate several large outliers. Both models show that the level of superparasitism declines with increasing host density, and the rate declines over time. It is proposed that the differing behaviours represented by the mixed model may reflect a balance between behavioural strategies of different selective benefit.

The relationship between dietary specialism and availability of food and water on cannibalistic interactions among predatory mites in protected crops.

The interplay between dietary specialism, the tolerance of food and water stress and level of cannibalism is likely to be important in determining the outcome of biological control using inundative releases of multiple natural enemies, such as phytoseiid mites in protected crops. The dietary specialist, Phytoseiulus persimilis, with a short immature development time (4-5 days) when plentiful food was available had a low ability to survive without food (5 days), even with access to water. The dietary generalists, Neoseiulus californicus, N. cucumeris and lphiseius degenerans, had longer immature development times (by up to 2 days) than P. persimilis. Survival ability differed amongst the generalist species when they were starved but provided with constant access to water. Both N. californicus and N. cucumeris survived the longest (8-10 days) and I. degenerans survived the shortest period (4 days). No negative intra-specific interaction between immatures was observed with P. persimilis when food was available and in the absence of food this species tended to starve rather than act cannibalistically. Both N. californicus and N. cucumeris showed a low degree of cannibalism between immatures, either when food was available, or when starved but given access to water. Even when food was available survival of I. degenerans fell by 30% in 4 days and remained at 60-70% for 3 further days; survival continued to decline rapidly when they were starved but provided with water. This indicates that immatures of I. degenerans could either feed on dead conspecifics or that they were capable of a degree of cannibalism. Adult females of P. persimilis did not feed on conspecific eggs even when deprived of food but provided with water. Adult female N. californicus and N. cucumeris did feed on conspecific eggs but at a low level (<1 egg per day), which occurred only after 48 h starvation. Although egg cannibalism occurred more consistently with adult female I. degenerans than with other mite species it was at a low level (<1 egg per day). If the tendency to cannibalism, not just of eggs but with more susceptible life stages such as larvae, is reduced when water is available freely this could be important in determining the interactions that occur under natural conditions.

Phytoseiid mites in protected crops: the effect of humidity and food availability on egg hatch and adult life span of Iphiseius degenerans, Neoseiulus cucumeris, N. californicus and Phytoseiulus persimilis (Acari: Phytoseiidae).

The effect of relative humidity on egg hatch success for Iphiseius degenerans, Neoseiulus californicus and N. cucumeris was described by a binomial model with a parallel slope. The shape of the response differed for Phytoseiulus persimilis and a model with separate parameters gave a significantly better fit. Fitted response curves showed that I. degenerans, N. cucumeris, N. californicus and P. persimilis were ranked by decreasing tolerance to low humidity, with egg mortalities of < 0.5, 3, 12 and 16% respectively at 75-80% RH at 20 degrees C. Egg stage duration for I. degenerans and N. cucumeris was unaffected over the range 60-82% RH. For N. californicus and P. persimilis egg duration was significantly longer at 60 and 70% than for either 82 or 90% RH. No effect of relative humidity was found on the mean life span of adult females when food was available continuously to the mites. N. californicus lived significantly longer (58 days after the first egg was laid) than the other species. No significant difference was observed in mean life span between adult females of I. degenerans and N. cucumeris (25 and 28 days respectively). The mean life span of adult female P. persimilis (19 days) was significantly shorter than the other species. In the absence of both food and water, the survival of adult female mites was reduced to 2-4 days. Survival time was at least doubled when free water was available in the absence of food. Mean survival of adult female mites with water but without food was 10 days for N. cucumeris, 18 days for N. californicus, 6 days for P. persimilis and 4 days for I. degenerans. Survival of adult female N. cucumeris and N. californicus was increased significantly, to 20 and 22 days respectively, when fungal hyphae were present along with water but in the absence of other food.