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Tag: Michael Strand

Reciprocal interactions between neuropeptide F and RYamide regulate host attraction in the mosquito Aedes aegypti

NPF accumulates in EECs of the posterior midgut after adult emergence but rapidly depletes after blood feeding.
NPF accumulates in EECs of the posterior midgut after adult emergence but rapidly depletes after blood feeding.

Female mosquitoes produce eggs in gonadotrophic cycles that are divided between a previtellogenic and vitellogenic phase. Previtellogenic females consume water and sugar sources like nectar while also being attracted to hosts for blood feeding. Consumption of a blood meal activates the vitellogenic phase, which produces mature eggs and suppresses host attraction. In this study, we tested the hypothesis that neuropeptide Y-like hormones differentially modulate host attraction behavior in the mosquito Aedes aegypti. A series of experiments collectively indicated that enteroendocrine cells (EECs) in the posterior midgut produce and release neuropeptide F (NPF) into the hemolymph during the previtellogenic phase which stimulates attraction to humans and biting behavior. Consumption of a blood meal, which primarily consists of protein by dry weight, down-regulated NPF in EECs until mature eggs developed, which was associated with a decline in hemolymph titer. NPF depletion depended on protein digestion but was not associated with EEC loss. Other experiments showed that neurons in the terminal ganglion extend axons to the posterior midgut and produce RYamide, which showed evidence of increased secretion into circulation after a blood meal. Injection of RYamide-1 and -2 into previtellogenic females suppressed host attraction, while coinjection of RYamides with or without short NPF-2 also inhibited the host attraction activity of NPF. Overall, our results identify NPF and RYamide as gut-associated hormones in A. aegypti that link host attraction behavior to shifts in diet during sequential gonadotrophic cycles.

Xiaoyi Dou, Kangkang Chen, Mark R Brown, Michael R Strand. Proc Natl Acad Sci U S A. 2024 Jul 9;121(28):e2408072121. doi: 10.1073/pnas.2408072121.

Identification of a viral gene essential for the genome replication of a domesticated endogenous virus in ichneumonid parasitoid wasps

Fig 6. RNAi knockdown of U16.
RNAi knockdown of U16.


Thousands of endoparasitoid wasp species in the families Braconidae and Ichneumonidae harbor “domesticated endogenous viruses” (DEVs) in their genomes. This study focuses on ichneumonid DEVs, named ichnoviruses (IVs). Large quantities of DNA-containing IV virions are produced in ovary calyx cells during the pupal and adult stages of female wasps. Females parasitize host insects by injecting eggs and virions into the body cavity. After injection, virions rapidly infect host cells which is followed by expression of IV genes that promote the successful development of wasp offspring. IV genomes consist of two components: proviral segment loci that serve as templates for circular dsDNAs that are packaged into capsids, and genes from an ancestral virus that produce virions. In this study, we generated a chromosome-scale genome assembly for Hyposotor didymator that harbors H. didymator ichnovirus (HdIV). We identified a total of 67 HdIV loci that are amplified in calyx cells during the wasp pupal stage. We then focused on an HdIV gene, U16, which is transcribed in calyx cells during the initial stages of replication. Sequence analysis indicated that U16 contains a conserved domain in primases from select other viruses. Knockdown of U16 by RNA interference inhibited virion morphogenesis in calyx cells. Genome-wide analysis indicated U16 knockdown also inhibited amplification of HdIV loci in calyx cells. Altogether, our results identified several previously unknown HdIV loci, demonstrated that all HdIV loci are amplified in calyx cells during the pupal stage, and showed that U16 is required for amplification and virion morphogenesis.

Ange Lorenzi, Fabrice Legeai, Véronique Jouan, Pierre-Alain Girard, Michael R Strand, Marc Ravallec, Magali Eychenne, Anthony Bretaudeau, Stéphanie Robin, Jeanne Rochefort, Mathilde Villegas, Gaelen R Burke, Rita Rebollo, Nicolas Nègre, Anne-Nathalie Volkoff. PLoS Pathog. 2024 Apr 25;20(4):e1011980. doi: 10.1371/journal.ppat.1011980.


On the origin and evolution of the mosquito male-determining factor Nix

Background and workflow.

The mosquito family Culicidae is divided into two subfamilies named the Culicinae and Anophelinae. Nix, the dominant male-determining factor, has only been found in the culicines Aedes aegypti and Ae. albopictus, two important arboviral vectors that belong to the subgenus Stegomyia. Here we performed sex-specific whole-genome sequencing and RNAseq of divergent mosquito species and explored additional male-inclusive datasets to investigate the distribution of Nix. Except for the Culex genus, Nix homologs were found in all species surveyed from the Culicinae subfamily, including 12 additional species from three highly divergent tribes comprising 4 genera, suggesting Nix originated at least 133-165 MYA. Heterologous expression of one of three divergent Nix ORFs in Ae. aegypti resulted in partial masculinization of genetic females as evidenced by morphology and doublesex splicing. Phylogenetic analysis suggests Nix is related to femaleless (fle), a recently described intermediate sex-determining factor found exclusively in anopheline mosquitoes. Nix from all species has a conserved structure, including three RNA-recognition motifs (RRMs), as does fle. However, Nix has evolved at a much faster rate than fle. The RRM3 of both Nix and fle are distantly related to the single RRM of a widely distributed and conserved splicing factor transformer-2 (tra2). RRM3-based phylogenetic analysis suggests this domain in Nix and fle may have evolved from tra2 or a tra2-related gene in a common ancestor of mosquitoes. Our results provide insights into the evolution of sex-determination in mosquitoes and will inform broad applications of mosquito-control strategies based on manipulating sex ratios towards the non-biting males.

James K Biedler, Azadeh Aryan, Yumin Qi, Aihua Wang, Ellen O Martinson, Daniel A Hartman, Fan Yang, Atashi Sharma, Katherine S Morton, Mark Potters, Chujia Chen, Stephen L Dobson, Gregory D Ebel, Rebekah C Kading, Sally Paulson, Rui-De Xue, Michael R Strand, Zhijian Tu. Mol Biol Evol. 2023 Dec 21:msad276. doi: 10.1093/molbev/msad276. Online ahead of print.

Increased environmental microbial diversity reduces the disease risk of a mosquitocidal pathogen

Fig 6 Ch_R13E2-SpR systemically infects A. aegypti larvae.
Fig 6 Ch_R13E2-SpR systemically infects A. aegypti larvae.

The host-specific microbiotas of animals can both reduce and increase disease risks from pathogens. In contrast, how environmental microbial communities affect pathogens is largely unexplored. Aquatic habitats are of interest because water enables environmental microbes to readily interact with animal pathogens. Here, we focused on mosquitoes, which are important disease vectors as terrestrial adults but are strictly aquatic as larvae. We identified a pathogen of mosquito larvae from the field as a strain of Chromobacterium haemolyticum. Comparative genomic analyses and functional assays indicate this strain and other Chromobacterium are mosquitocidal but are also opportunistic pathogens of other animals. We also identify a critical role for diversity of the environmental microbiota in disease risk. Our study characterizes both the virulence mechanisms of a pathogen and the role of the environmental microbiota in disease risk to an aquatic animal of significant importance to human health.

Zhiwei Kang, Vincent G Martinson, Yin Wang, Kerri L Coon, Luca Valzania, Michael R Strand. mBio. 2023 Dec 6:e0272623. doi: 10.1128/mbio.02726-23.

The mosquito Aedes aegypti requires a gut microbiota for normal fecundity, longevity and vector competence

Mosquitoes shift from detritus-feeding larvae to blood-feeding adults that can vector pathogens to humans and other vertebrates. The sugar and blood meals adults consume are rich in carbohydrates and protein but are deficient in other nutrients including B vitamins. Facultatively hematophagous insects like mosquitoes have been hypothesized to avoid B vitamin deficiencies by carryover of resources from the larval stage. However, prior experimental studies have also used adults with a gut microbiota that could provision B vitamins. Here, we used Aedes aegypti, which is the primary vector of dengue virus (DENV), to ask if carryover effects enable normal function in adults with no microbiota. We show that adults with no gut microbiota produce fewer eggs, live longer with lower metabolic rates, and exhibit reduced DENV vector competence but are rescued by provisioning B vitamins or recolonizing the gut with B vitamin autotrophs. We conclude carryover effects do not enable normal function.

Ruby E Harrison, Xiushuai Yang, Jai Hoon Eum, Vincent G Martinson, Xiaoyi Dou, Luca Valzania, Yin Wang, Bret M Boyd, Mark R Brown, Michael R Strand. Commun Biol. 2023 Nov 13;6(1):1154. doi: 10.1038/s42003-023-05545-z.

Insulin-like peptides and ovary ecdysteroidogenic hormone differentially stimulate physiological processes regulating egg formation in the mosquito Aedes aegypti

graphical abstract

Mosquitoes including Aedes aegypti are human disease vectors because females must blood feed to produce and lay eggs. Blood feeding triggers insulin-insulin growth factor signaling (IIS) which regulates several physiological processes required for egg development. A. aegypti encodes 8 insulin-like peptides (ILPs) and one insulin-like receptor (IR) plus ovary ecdysteroidogenic hormone (OEH) that also activates IIS through the OEH receptor (OEHR). In this study, we assessed the expression of A. aegypti ILPs and OEH during a gonadotropic cycle and produced each that were functionally characterized to further understand their roles in regulating egg formation. All A. aegypti ILPs and OEH were expressed during a gonadotropic cycle. Five ILPs (1, 3, 4, 7, 8) and OEH were specifically expressed in the head, while antibodies to ILP3 and OEH indicated each was released after blood feeding from ventricular axons that terminate on the anterior midgut. A subset of ILP family members and OEH stimulated nutrient storage in previtellogenic females before blood feeding, whereas most IIS-dependent processes after blood feeding were activated by one or more of the brain-specific ILPs and/or OEH. ILPs and OEH with different biological activities also exhibited differences in IIS as measured by phosphorylation of the IR, phosphoinositide 3-kinase/Akt kinase (AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK). Altogether, our results provide the first results that compare the functional activities of all ILP family members and OEH produced by an insect.

Kangkang Chen, Xiaoyi Dou, Jai Hoon Eum, Ruby A Harrison, Mark R Brown, Michael R Strand. Insect Biochem Mol Biol. 2023 Oct 30:104028. doi: 10.1016/j.ibmb.2023.104028.

Functional characterization of Microplitis demolitor bracovirus genes that encode nucleocapsid

Fig 2 Virion morphogenesis (phases 1–4) in calyx cells from newly emerged adult females injected with ds-eGFP (control) (A–D) or ds-vp39 (E–H).


Bracoviruses (BVs) are endogenized nudiviruses in parasitoid wasps of the microgastroid complex (order Hymenoptera: Family Braconidae). BVs produce replication-defective virions that adult female wasps use to transfer DNAs encoding virulence genes to parasitized hosts. Some BV genes are shared with nudiviruses and baculoviruses with studies of the latter providing insights on function, whereas other genes are only known from nudiviruses or other BVs which provide no functional insights. A proteomic analysis of Microplitis demolitor bracovirus (MdBV) virions recently identified 16 genes encoding nucleocapsid components. In this study, we further characterized most of these genes. Some nucleocapsid genes exhibited early or intermediate expression profiles, while others exhibited late expression profiles. RNA interference (RNAi) assays together with transmission electron microscopy indicated vp39HzNVorf9-like2HzNVorf93-likeHzNVorf106-likeHzNVorf118-likeand 27b are required to produce capsids with a normal barrel-shaped morphology. RNAi knockdown of vlf-1avlf-1b-1vlf-1b-2int-1, and p6.9-1 did not alter the formation of barrel-shaped capsids but each reduced processing of amplified proviral segments and DNA packaging as evidenced by the formation of electron translucent capsids. All of the genes required for normal capsid assembly were also required for proviral segment processing and DNA packaging. Collectively, our results deorphanize several BV genes with previously unknown roles in virion morphogenesis.IMPORTANCEUnderstanding how bracoviruses (BVs) function in wasps is of broad interest in the study of virus evolution. This study characterizes most of the Microplitis demolitor bracovirus (MdBV) genes whose products are nucleocapsid components. Results indicate several genes unknown outside of nudiviruses and BVs are essential for normal capsid assembly. Results also indicate most MdBV tyrosine recombinase family members and the DNA binding protein p6.9-1 are required for DNA processing and packaging into nucleocapsids.

Ange Lorenzi, Michael J Arvin, Gaelen R Burke, Michael R Strand. J Virol. 2023 Oct 25:e0081723. doi: 10.1128/jvi.00817-23.

All the pieces matter: UGA researchers collaborate to solve malaria puzzle

malaria parasites
Super-resolution microscopy showing malaria parasites infecting human red blood cells. credit: Muthugapatti Kandasamy, Biomedical Microscopy Core

They say what doesn’t kill you makes you stronger. Whoever coined that adage had probably never heard of Plasmodium.

It’s a microscopic parasite, invisible to the naked eye but common in tropical and subtropical regions throughout the world. Each year, millions of people are infected by Plasmodium and exposed to an even more debilitating—and often deadly—disease: malaria.

Malaria is one of the deadliest diseases known to man. It can lead to extreme illness, marked by fever, chills, headaches and fatigue. More than half the world’s population is at risk of contracting the disease, and those who develop relapsing infections suffer a host of associated costs.

Limited educational opportunities and wage loss lead to an often unbreakable cycle of poverty. Vulnerable populations are most at risk.

“When I’m teaching in an endemic area like Africa, it isn’t unusual to find a student who needs to sleep during part of the workshop because they have malaria,” researcher Jessica Kissinger said.

It’s a challenge she and her collaborators in the University of Georgia’s Center for Tropical and Emerging Global Diseases (CTEGD) are trying to combat.

When the Center was established in 1998, there were only a couple of faculty members studying Plasmodium. Now, 25 years later, it has become a world-class powerhouse of multidisciplinary malaria research. Scientists examine various species of the dangerous parasite, studying its life cycle and the mosquito that transmits it.

While Plasmodium seems to have superpowers that allow it to evade detection and resist treatment, CTEGD researchers are working together to innovate and transfer science from the lab to interventions on the ground.

A 50,000-piece puzzle with no edges

Plasmodium is a complex organism, and studying it is like putting together a jigsaw puzzle. Some researchers contribute pieces related to the blood or liver stages of the parasite’s lifecycle, while others provide insights about hosts interactions. One way UGA’s research connects with the global effort to eradicate malaria is PlasmoDb—a resource derived in part from Kissinger’s research that is now part of a host of databases under the umbrella of The Eukaryotic Pathogen, Vector and Host information Resource (VEuPathDB).

“Our group has been able to help many others when their research question crosses into an –omic,” Kissinger said, referring to in-house shorthand for domains like genomics, proteomics and metabolomics.

Kissinger, Distinguished Research Professor of genetics in the Franklin College of Arts & Sciences, became interested in malaria and Plasmodium during her postdoctoral training at the National Institutes of Health (NIH). Working from an evolutionary biology perspective, she’s interested in how the parasite has changed over time.

PlasmoDb, a database of Plasmodium informatics resources, is a tool developed in part by the work of Distinguished Research Professor Jessica Kissinger, who became interested in malaria during her postdoctoral training at the National Institutes of Health.

“I see it as an arms race,” Kissinger said. “I want to understand what moves they have and can make.”

To understand the parasite, you must dive deep into its genetic code.

Kissinger paired her work in Plasmodium genomics with her interest in computing by helping create the database with information from the Plasmodium genome project completed in 2002. The Malaria Host-Pathogen Interaction Center, one of her projects at UGA, was a seven-year, multi-institutional effort funded, in part, by NIH to create data sets that could be used in systems biology of the host-pathogen interaction during the development of disease.

“Wouldn’t it be neat if, from the beginning of infection all the way to cure, you knew everything that was going on in the organism all the time?” Kissinger said, noting the project’s goal.

They generated terabytes of data that, along with data from the global research community, are publicly accessible and reusable through PlasmoDB and other resources.

Being part of a group that is studying so many different aspects of malaria helps put Kissinger’s research into perspective. Now, in addition to understanding the parasite, she also thinks about tools needed to facilitate research from peers.

High-tech solutions rely on basic research

David Peterson, professor of infectious diseases in the College of Veterinary Medicine, noted that low-tech solutions have mitigated malaria’s human costs. He acknowledged, however, that their long-term goals required more.

“We have to acknowledge that low-tech solutions, such as mosquito nets, have saved lives,” Peterson said. “But to develop the high-tech solutions that will one day end malaria, we need basic research.”

Pregnant women are particularly vulnerable to malaria because their existing immunity to malaria fails to protect them during pregnancy. Placental malaria often results in  premature birth and low birth weight.

Peterson is interested in a binding protein that allows the parasite to adhere to the placenta. While many P. falciparum parasites have only one gene copy that encodes the placental binding protein,  Peterson is investigating Plasmodiumisolates with two or more slightly different copies.

But why isn’t one copy enough?

David Peterson
Professor David Peterson of the College of Veterinary Medicine acknowledges the importance of low-tech solutions like mosquito nets but said to mitigate its effects required better understanding at the genetic level.

That is the primary question Peterson is focused on. He wants to understand how Plasmodium uses extra copies to evade the immune system, distinguishing the role of each requires tools that Vasant Muralidharan, associate professor of cellular biology, has.

Muralidharan’s interest began when he contracted malaria himself. Through access to good health care, he made a full recovery, but the pain he endured remained. He wanted to understand this parasite. Even more, he wanted to make an impact with research.

His graduate training focused on biophysics, but soon his interest in Plasmodium resurfaced. He discovered there was a lack of tools to study the parasite on a genetic level.

“It’s like a house of cards, and each card is a gene,” Muralidharan said. “You can remove one and see what happens—does the house fall or remain standing?”

This is an illustration of the life cycle of the parasites of the genus, Plasmodium, that are causal agents of malaria.(Illustration by CDC/ Alexander J. da Silva, PhD; Melanie Moser)

In the days before CRISPR/Cas9, there wasn’t a precise way to remove genes. Muralidharan is among the pioneers of gene-editing techniques in Plasmodium.

Like Peterson, Muralidharan focuses on proteins secreted by the parasite. He studies the largely unknown process that allows the parasite to invade a red blood cell (RBC), replicate and escape. The lack of tools was a major hindrance, so Muralidharan created new ones.

These tools have been used by Muralidharan’s CTEGD and CDC colleagues to see how drugs might fail. Muralidharan’s laboratory can create mutant Plasmodium parasites that become resistant to a particular drug, and genome sequence databases allow researchers to check if that mutant is already circulating in malaria endemic regions.

Vasant Quote

Building a research bridge to endemic regions

Plasmodium vivax is the predominant malaria parasite in Southeast Asia. It causes “relapsing malaria” during which some parasites go “dormant” after entering the liver instead of reproducing. This phase is a major obstacle for current treatments.

CTEGD Director Dennis Kyle, GRA Eminent Scholar Chair in Antiparasitic Drug Discovery and head of the Department of Cellular Biology, became fascinated with the Plasmodium parasite early in his career, spending time living in Thailand and working in refugee camps where malaria is prevalent.

Dennis Kyle
CTEGD Director Dennis Kyle was moved to follow through with his work as a researcher on a trip to a refugee camp in Thailand. Upon seeing the challenges residents faced, he thought perhaps he should have become a physician. Instead, a local leader impressed upon him the impact you could have in generating new treatments that could benefit everyone. (Photo by Andrew Davis Tucker/UGA)

“When I first got to the refugee camp and saw the situation people were living in, I questioned my decision to become a scientist in the lab instead of becoming a physician,” Kyle said, recalling a camp he worked in that housed about 1,300 kids between the ages of 2 and 15. “There was a guy who was a leader in the group who probably had no more than an early high school education. He said, ‘Look at what you can do—you might generate something that would benefit all of us. The physicians we have in the camp can only work on a few people at a time.’”

Kyle’s laboratory is looking to repurpose medications that have antimalarial properties, a safe way to reduce the development time from lab to clinical use. He’s optimistic we will see a drug treatment that eliminates vivax malaria.

“That’s where UGA is playing a major role,” he said. “The Gates Foundation funded us to develop tools to study the dormant parasite in the liver. And we’ve been successful.”

One of Kyle’s collaborators is Samarchith Kurup, assistant professor of cellular biology, who studies the human immune response to Plasmodium infection.

“We use mouse models to delve into the fundamental host-parasite interactions, which you cannot do practicallyin humans,” Kurup said. “Our understanding of these fundamental processes gives rise to newer and better vaccination approaches and drugs.”

Another important CTEGD addition is Chet Joyner, assistant professor of infectious diseases, whose work has helped make it easier to study dormant parasites stateside.

Like other Plasmodium researchers, Joyner became interested in parasites at an early age. During an undergraduate parasitology class, he discovered how little was known about P. vivax. He was already interested in how diseases develop, so for graduate school he focused on the liver stage of vivax malaria. However, it was a difficult task.

Samarchith Kurup is an assistant professor of cellular biology studying the human immune response to Plasmodium infection. (photo credit: Lauren Corcino)
Samarchith Kurup is an assistant professor of cellular biology studying the human immune response to Plasmodium infection. (photo credit: Lauren Corcino)
Chet Joyner
Assistant Professor Chet Joyner discovered how little was known about Plasmodium vivax as an undergraduate student.

“At the time, the technologies weren’t there,” Joyner said. “Dennis was working on his system, but it wasn’t on the scene yet. I changed from studying the parasite to studying the animal model to understand pathogenesis and immunology in humans.”

Joyner joined UGA after completing his postdoctoral training at Emory University, where he developed a non-mouse animal model to study vivax malaria.

“We have to go to [Thailand] where people are infected and collect blood samples and then feed mosquitoes these samples to do the necessary studies,” Kyle said. “That’s been very impactful. We’ve gotten a lot of data out of it, and now with Chet’s model it all can be done under one roof.”

Joyner wants to understand the human immune response with a focus on vaccine development. Building on Muralidharan’s and other researchers’ findings of how the parasite interacts with the RBCs, Joyner’s vaccine program targets a specific protein in the parasite that inhibits the development of immunity.

“My colleagues have shown that if you knock this protein out in the parasite, the immune response in mice is actually great, and we are now working together to evaluate this in non-mouse models.” Joyner said.

Joyner also has collaborated with Belen Cassera, professor of biochemistry, to screen drug compounds. Cassera’s training focused on metabolism to find drug targets. She is particularly interested in how a drug functions.

“If we understand how the drug works, it will help us predict potential side effects in humans,” Cassera said. “We can’t predict everything, but knowing how it works gives you some confidence in whether it will work in humans.”

Cassera is focused on finding drugs that will treat the more lethal Plasmodium falciparum, the predominant species in Africa, which is rapidly becoming resistant to current treatments. Her work is complementary to Kyle’s.

“They run certain assays for the liver-stage infection, and our lab benefits because we want to know if the drug we are developing is specific for the blood stage or can tackle all stages,” Cassera said.

M. Belen Cassera
Professor Belen Cassera is identifying drugs that will treat the lethal Plasmodium falciparum, a predominant species of the parasite in Africa that has become resistant to many current treatments.

Don’t forget the mosquito

“Malaria is a vector-borne disease transmitted by a mosquito. You need to tackle not only the parasite in the human but also stop its transmission,” Cassera said. “CTEGD is unique because we can study the whole life cycle, including the mosquito.”

Michael Strand, H.M. Pulliam Chair of Entomology in the College of Agricultural and Environmental Sciences and a National Academy of Sciences Fellow, is an expert on parasite-host interactions. Instead of the human host, he is interested in mosquitoes. Recent work indicates blood feeding behavior of mosquitoes strongly affects malaria parasite development while the gut microbiota of mosquitos could lead to new ways to control populations. Having the SporoCore insectory on campus aids his research.

Michael Strand is an expert on parasite-host interactions. His research focuses on mosquitoes and their effects on malaria parasite development.
Michael Strand is an expert on parasite-host interactions. His research focuses on mosquitoes and their effects on malaria parasite development.

Established in 2020, SporoCore, under the management of Ash Pathak, assistant research scientist in the Department of Infectious Diseases, provides both uninfected and Plasmodium-infected Anopheles stephensi mosquitoes to researchers at UGA and other institutions. Like Joyner’s animal model, the insectory allows for research to be done in the U.S. that would otherwise require field work in an endemic country.

Old-school interventions like mosquito nets, combined with new drug therapies, have reduced the number of malaria deaths, which declined over the last 30 years before rising slightly during the COVID-19 pandemic. Great strides have been made to control and treat malaria—but not enough. New tools, like the ones being developed at CTEGD, are needed to keep pushing malaria’s morbidity and mortality rates in the right direction.

“The hard part—what can’t be done easily with the tools we already have—is being done,” Kyle said. “We just need new tools, which is one of the things that our center is really a leader in.”


This story was first published at

An aphid symbiont confers protection against a specialized RNA virus, another increases vulnerability to the same pathogen

Insects often harbor heritable symbionts that provide defense against specialized natural enemies, yet little is known about symbiont protection when hosts face simultaneous threats. In pea aphids (Acyrthosiphon pisum), the facultative endosymbiont Hamiltonella defensa confers protection against the parasitoid, Aphidius ervi, and Regiella insecticola protects against aphid-specific fungal pathogens, including Pandora neoaphidis. Here we investigated whether these two common aphid symbionts protect against a specialized virus A. pisum virus (APV), and whether their anti-fungal and anti-parasitoid services are impacted by APV infection. We found that APV imposed large fitness costs on symbiont-free aphids and these costs were elevated in aphids also housing H. defensa. In contrast, APV titers were significantly reduced and costs to APV infection were largely eliminated in aphids with R. insecticola. To our knowledge, R. insecticola is the first aphid symbiont shown to protect against a viral pathogen, and only the second arthropod symbiont reported to do so. In contrast, APV infection did not impact the protective services of either R. insecticola or H. defensa. To better understand APV biology, we produced five genomes and examined transmission routes. We found that moderate rates of vertical transmission, combined with horizontal transfer through food plants, were the major route of APV spread, although lateral transfer by parasitoids also occurred. Transmission was unaffected by facultative symbionts. In summary, the presence and species identity of facultative symbionts resulted in highly divergent outcomes for aphids infected with APV, while not impacting defensive services that target other enemies. These findings add to the diverse phenotypes conferred by aphid symbionts, and to the growing body of work highlighting extensive variation in symbiont-mediated interactions.

C H V Higashi, W L Nichols, G Chevignon, V Patel, S E Allison, K L Kim, M R Strand, K M Oliver. Mol Ecol. 2022 Dec 2. doi: 10.1111/mec.16801. Online ahead of print.

Multiple endocrine factors regulate nutrient mobilization and storage in Aedes aegypti during a gonadotrophic cycle

Anautogenous mosquitoes must blood feed on a vertebrate host to produce eggs. Each gonadotrophic cycle is subdivided into a sugar-feeding previtellogenic phase that produces primary follicles and a blood meal-activated vitellogenic phase in which large numbers of eggs synchronously mature and are laid. Multiple endocrine factors including juvenile hormone (JH), insulin-like peptides (ILPs), ovary ecdysteroidogenic hormone (OEH) and 20-hydroxyecdysone (20E) coordinate each gonadotrophic cycle. Egg formation also requires nutrients from feeding that are stored in the fat body. Regulation of egg formation is best understood in Aedes aegypti but the role different endocrine factors play in regulating nutrient mobilization and storage remains unclear. In this study, we report that adult female Ae. aegypti maintained triacylglycerol (TAG) stores during the previtellogenic phase of the first gonadotrophic cycle while glycogen stores declined. In contrast, TAG and glycogen stores were rapidly mobilized during the vitellogenic phase and then replenishment. Several genes encoding enzymes with functions in TAG and glycogen metabolism were differentially expressed in the fat body, which suggested regulation was mediated in part at the transcriptional level. Gain of function assays indicated that stored nutrients were primarily mobilized by adipokinetic hormone (AKH) while juvenoids and OEH regulated replenishment. ILP3 further showed evidence of negatively regulating certain lipolytic enzymes. Loss of function assays further indicated AKH depends on the AKH receptor (AKHR) for function. Altogether, our results indicate that the opposing activities of different hormones regulate nutrient stores during a gonadotrophic cycle in Ae. aegypti. This article is protected by copyright. All rights reserved.

Xiaoyi Dou, Kangkang Chen, Mark R Brown, Michael R Strand. Insect Sci. 2022 Sep 2. doi: 10.1111/1744-7917.13110.