Determining Temperature Preference of Mosquitoes and Other Ectotherms

Most insects and other ectotherms have a relatively narrow optimal temperature window, and deviation from their optima can have significant effects on ...

University of Liverpool

Experimental evidence is accumulating that endosymbionts of phytophagous insects may transmit horizontally via plants. Intracellular symbionts known for manipulating insect reproduction and altering fitness (, and bacterial parasite of the leafhopper ) have been found to travel from infected insects into plants. Other insects, either of the same or different species can acquire the symbiont from the plant through feeding, and in some cases transfer it to their progeny. These reports prompt many questions regarding how intracellular insect symbionts are delivered to plants and how they affect them. Are symbionts passively transported along the insect-plant-insect path, or do they actively participate in the process? How widespread are these interactions? How does symbiont presence influence the plant? And what conditions are required for the new infection to establish in an insect? From an ecological, evolutionary, and applied perspective, this mode of horizontal transmission could have profound implications if occurring frequently enough or if new stable symbiont infections are established. Transmission of symbionts through plants likely represents an underappreciated means of infection, both in terms of symbiont epidemiology and the movement of symbionts to new host species.

Horizontal Transmission of Intracellular Insect Symbionts via Plants.

 (, ) is an intraovarially transmitted symbiont of insects able to exert striking phenotypes, including reproductive manipulations and pathogen blocking. These phenotypes make  a promising tool to combat mosquito-borne diseases. Although  is present in the majority of terrestrial arthropods, including many disease vectors, it was considered absent from  mosquitos, the main vectors of malaria in sub-Saharan Africa. In 2014,  sequences were detected in  samples collected in Burkina Faso. Subsequently, similar evidence came from collections all over Africa, revealing a high  16S rRNA sequence diversity, low abundance, and a lack of congruence between host and symbiont phylogenies. Here, we reanalyze and discuss recent evidence on the presence of  sequences in  We find that although detected at increasing frequencies, the unusual properties of these  sequences render them insufficient to diagnose natural infections in  Future studies should focus on uncovering the origin of  sequence variants in  and seeking sequence-independent evidence for this new symbiosis. Understanding the ecology of  mosquitos and their interactions with  will be key in designing successful, integrative approaches to limit malaria spread. Although the prospect of using  to fight malaria is intriguing, the newly discovered strains do not bring it closer to realization.  mosquitos are the main vectors of malaria, threatening around half of the world's population. The bacterial symbiont  can interfere with disease transmission by other important insect vectors, but until recently, it was thought to be absent from natural  populations. Here, we critically analyze the genomic, metagenomic, PCR, imaging, and phenotypic data presented in support of the presence of natural  infections in  We find that they are insufficient to diagnose  infections and argue for the need of obtaining robust data confirming basic  characteristics in this system. Determining the  infection status of  is critical due to its potential to influence  population structure and  transmission.

Is Anopheles gambiae a Natural Host of ?

Vector-borne viral diseases pose an urgent public health challenge, particularly in the tropics. Field releases of mosquitoes carrying bacterial symbionts that reduce vector competence are ongoing in Kuala Lumpur, Malaysia. Early results show that wAlbB Wolbachia can persist in mosquitoes in urban settings and decrease dengue incidence in humans.

Infectious Diseases: Antiviral Wolbachia Limits Dengue in Malaysia.

The outcome of natural enemy attack in insects is commonly influenced by the presence of protective symbionts in the host. The degree to which protection functions in natural populations, however, will depend on the robustness of the phenotype and symbiosis to variation in the abiotic environment. We studied the impact of a key environmental parameter-temperature-on the efficacy of the protective effect of the symbiont Spiroplasma on its host Drosophila hydei, against attack by the parasitoid wasp Leptopilina heterotoma. In addition, we investigated the thermal sensitivity of the symbiont's vertical transmission, which may be a key determinant of the ability of the symbiont to persist. We found that vertical transmission was more robust than previously considered, with Spiroplasma being maintained at 25°C, at 18°C and with 18/15°C diurnal cycles, with rates of segregational loss only increasing at 15°C. Protection against wasp attack was ablated before symbiont transmission was lost, with the symbiont failing to rescue the fly host at 18°C. We conclude that the presence of a protective symbiosis in natural populations cannot be simply inferred from the presence of a symbiont whose protective capacity has been tested under narrow controlled conditions. More broadly, we argue that the thermal environment is likely to represent an important determinant of the evolutionary ecology of defensive symbioses in natural environments, potentially driving seasonal, latitudinal and altitudinal variation in symbiont frequency.

Thermal sensitivity of the Spiroplasma-Drosophila hydei protective symbiosis: The best of climes, the worst of climes.

Wolbachia is a maternally transmitted bacterium that is widespread in arthropods and filarial nematodes and confers strong antiviral protection in Drosophila melanogaster and other arthropods. -transinfected Aedes aegypti mosquitoes are currently being deployed to fight transmission of dengue and Zika viruses. However, the mechanism of antiviral protection and the factors influencing are still not fully understood. Here, we show that temperature modulates -conferred protection in Drosophila melanogaster. Temperature after infection directly impacts  C virus (DCV) replication and modulates  protection. At higher temperatures, viruses proliferate more and are more lethal, while  confers lower protection. Strikingly, host developmental temperature is a determinant of -conferred antiviral protection. While there is strong protection when flies develop from egg to adult at 25°C, the protection is highly reduced or abolished when flies develop at 18°C. However, -induced changes during development are not sufficient to limit virus-induced mortality, as  is still required to be present in adults at the time of infection. This developmental effect is general, since it was present in different host genotypes,  variants, and upon infection with different viruses. Overall, we show that -conferred antiviral protection is temperature dependent, being present or absent depending on the environmental conditions. This interaction likely impacts -host interactions in nature and, as a result, frequencies of host and symbionts in different climates. Dependence of -mediated pathogen blocking on developmental temperature could be used to dissect the mechanistic bases of protection and influence the deployment of  to prevent transmission of arboviruses.  Insects are often infected with beneficial intracellular bacteria. The bacterium  is extremely common in insects and can protect them from pathogenic viruses. This effect is being used to prevent transmission of dengue and Zika viruses by -infected mosquitoes. To understand the biology of insects in the wild, we need to discover which factors affect -conferred antiviral protection. Here, we show that the temperature at which insects develop from eggs to adults can determine the presence or absence of antiviral protection. The environment, therefore, strongly influences this insect-bacterium interaction. Our work may help to provide insights into the mechanism of viral blocking by , deepen our understanding of the geographical distribution of host and symbiont, and incentivize further research on the temperature dependence of conferred protection for control of mosquito-borne disease.

-Conferred Antiviral Protection Is Determined by Developmental Temperature.

The genus  has been traditionally considered to comprise heritable bacterial symbionts of arthropods. Recent work has reported a microbe related to the type species  as infecting the honey bee, . The association was unusual for members of the genus in that the microbe-host interaction arose through environmental and social exposure rather than vertical transmission. In this study, we describe the  culture of ArsBeeUS, a strain of this microbe isolated from  in the USA. The 16S rRNA sequence of the isolated strain indicates it falls within the genus . Biolog analysis indicates the bacterium has a restricted range of nutrients that support growth.  experiments demonstrate the strain proliferates rapidly on injection into  hosts. We further report the closed genome sequence for the strain. The genome is 3.3 Mb and the G+C content is 37.6 mol%, which is smaller than  but larger than the genomes reported for non-culturable  symbionts. The genome is complex, with six extrachromosomal elements and 11 predicted intact phage elements, but notably less complex than . Strain ArsBeeUS is clearly distinct from the type species  on the basis of genome sequence, with 92 % average nucleotide identity. Based on our results, we propose  sp. nov., with the type strain ArsBeeUS (CECT 30499=DSM113403=LMG 32504).

Ewa Chrostek

Department of Evolution,
Ecology,
and Behavior,
Institute of Infection,
Veterinary and Ecological Sciences,
Department of Evolution, Ecology, and Behavior, Institute of Infection, Veterinary and Ecological Sciences

University of Liverpool

Determining Temperature Preference of Mosquitoes and Other Ectotherms

Ewa Chrostek

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Evolution,Ecology,and Behavior,Institute of Infection,Veterinary and Ecological Sciences,Department of Evolution, Ecology, and Behavior, Institute of Infection, Veterinary and Ecological Sciences

University of Liverpool

Determining Temperature Preference of Mosquitoes and Other Ectotherms

Department of Evolution,
Ecology,
and Behavior,
Institute of Infection,
Veterinary and Ecological Sciences,
Department of Evolution, Ecology, and Behavior, Institute of Infection, Veterinary and Ecological Sciences