Michael Strand Archives - Center for Tropical and Emerging Global Diseases

Four nudivirus core genes present in the genome of Venturia canescens are required for virus-like particle formation and prevention of encapsulation of parasitoid wasp eggs

Donna Huber on November 20, 2025

Fig 1 VcVLP morphogenesis in calyx cells from different aged pupae or newly emerged adults that were injected with ds-egfp when P1 pupae.

Venturia canescens is a parasitoid wasp that harbors a domesticated endogenous virus (DEV) and parasitizes host insects like Ephestia kuehniella. The V. canescens DEV evolved from an alphanudivirus and produces virus-like particles (VLPs) in females that protect wasp eggs from a host immune defense called encapsulation. In contrast, very few DEV genes required for VLP formation and function have been identified. In this study, we characterized five V. canescens DEV genes of unknown function that all nudiviruses encode. Three of these genes are single copy (OrNVorf18-like, OrNVorf61-like, and OrNVorf76-like), while OrNVorf41-like has expanded into a six-member family and OrNVorf47-like has expanded into a three-member family. Sequence analysis indicated all of these genes retain essential motifs present in nudivirus homologs, while transmission electron microscopy (TEM) studies characterized the timing of VLP formation during the wasp pupal stage. RNA interference (RNAi) assays identified OrNVorf18-like, OrNVorf61-like, OrNVorf41-like-1, and OrNVorf41-like-2 as genes that are required for normal VLP formation. Knockdown of OrNVorf47-like family members did not affect VLP formation but did disable binding of VLPs to V. canescens eggs and protection against encapsulation. Disabled formation of VLPs in response to RNAi knockdown of OrNVorf18-like, OrNVorf61-like, OrNVorf41-like-1, and OrNVorf41-like-2 also resulted in wasp eggs being encapsulated. In contrast, knockdown of OrNVorf76-like had no effect on VLP assembly, egg binding, or encapsulation. Altogether, reported results significantly advance our understanding of V. canescens VLP (VcVLP) formation and function.

Importance: Understanding how V. canescens coopted an alphanudivirus to produce VcVLPs is of interest to the study of virus evolution. Our results show that three nudivirus core genes have essential functions in VcVLP formation, while one is essential for the novel function of binding to wasp eggs and protection from encapsulation, which is the most important immune defense of insects against parasitoids.

Meng Mao, Corinne M Stouthamer, Ange Lorenzi, Michael R Strand, Gaelen R Burke. J Virol. 2025 Nov 20:e0130525. doi: 10.1128/jvi.01305-25.

Large DNA Viruses That Parasitoid Wasps Transmit to Hosts

Donna Huber on October 7, 2025

Many types of viruses have been identified in parasitoid wasps and other Hymenoptera. Parasitoid wasps also transmit several viruses to hosts through the piercing ovipositors that females use to lay eggs. Most viruses that are known to be transmitted by parasitoids have large double-stranded DNA genomes. We summarize the range of interactions that have evolved between parasitoid wasps and the viruses they transmit. Some viruses are mechanically transmitted to hosts, which can reduce the fitness of wasp offspring. Others have evolved into beneficial symbionts or reproductive parasites that replicate in wasps and hosts. Some large dsDNA viruses have also been co-opted into domesticated endogenized viruses that are vertically transmitted to offspring but still produce virions or virus-like particles that wasps use to parasitize hosts. We conclude by discussing future directions and why parasitoid wasps likely transmit many more viruses than are currently known.

Michael R Strand, Kelsey A Coffman, Gaelen R Burke. Annu Rev Entomol. 2025 Oct 7. doi: 10.1146/annurev-ento-121423-013425.

Insulin-like peptides activate egg formation in the Asian malaria mosquito Anopheles stephensi

Donna Huber on October 7, 2025

Background: The mosquito family Culicidae diverged into the subfamilies Anophelinae and Culicinae approximately 179 million years ago. Most female mosquitoes are anautogenous and must blood-feed on a vertebrate to produce eggs. Regulation of egg-producing gonotrophic cycles is best understood in the culicine Aedes aegypti. Anopheline mosquitoes encode all of the hormones that regulate gonotrophic cycles in Ae. aegypti, but the processes regulating egg formation may not be fully similar. In this study, we conducted experiments that compared egg formation in Anopheles stephensi to prior findings reported for Ae. aegypti.

Methods: Assays for yolk deposition into oocytes, ovary ecdysteroidogenesis, vitellogenin expression, nutrient storage and oviposition were used to characterize gonotrophic cycles in An. stephensi females that were mated or unmated.

Results: Yolk deposition into oocytes depended on the release of hormones produced in the head. Two insulin-like peptides, An. stephensi insulin-like peptide hormone 3 (AsILP3) and AsILP4, stimulated the vitellogenic phase in An. stephensi, as measured by several different assays, whereas ovary ecdysteroidogenic hormone (OEH) showed no stimulatory activity. Nutrient stores were lower in An. stephensi than Ae. aegypti, which was associated with females also being unresponsive to AsILP3 stimulation in the absence of a blood meal. Anopheles stephensi males transferred ecdysteroids (ECDs) to females, which was associated with mated females producing and laying more eggs than unmated females. However, mated and unmated females did not show differences in ECD production by the ovaries or vitellogenin expression at the messenger RNA level by the fat body. Most females that mated before consuming a first blood meal oviposited while most unmated females did not. Mating after consuming a first blood meal did not rescue oviposition. However, females that reabsorbed eggs and consumed a second blood meal did oviposit.

Conclusions: Regulation of gonotrophic cycles in An. stephensi shares some features with Ae. aegypti but also exhibits differences.

Benjamin L Phipps, Mark R Brown, Michael R Strand. Parasit Vectors. 2025 Oct 7;18(1):399. doi: 10.1186/s13071-025-07036-y.

Recent insights in the development and functions of insect hemocytes

Donna Huber on September 15, 2025

Figure 1. Cellular defense responses, humoral effector molecules and regulators of hemocyte functions in insects. In the center of the figure is a stylized image of an insect hemocyte. The arrow to the left points to the four major cellular defenses that are mediated by hemocytes. The arrow to the right points to five of the most important humoral effector molecules hemocytes produce. The upper arrow points to key receptors with functions in regulating hemocyte-mediated cellular defenses, while the lower arrow points to cytokines that regulate hemocyte functions or communication between hemocytes and other tissues. Small case statements below some headings provide brief explanations of terms while additional details are presented in the main text. — Figure 1. Cellular defense responses, humoral effector molecules and regulators of hemocyte functions in insects.

Hemocytes mediate defense responses that are collectively referred to as cellular immunity. Here I highlight recent progress in the study of hemocyte ontogeny and function. Studies conducted primarily in D. melanogaster, mosquitoes and Lepidoptera identify a number of transcription factors and signaling pathways that regulate hemocyte differentiation and proliferation. Recent single cell RNA sequencing studies identify genes that distinguish transitional states in different hemocyte populations and changes that occur during immune responses. Several new studies expand understanding of the functions of sessile hemocytes. Recent results also enhance understanding of the signaling pathways that regulate hemocyte functions.

Michael R Strand. Curr Opin Insect Sci. 2025 Sep 15:101434. doi: 10.1016/j.cois.2025.101434.

Protocol for detecting peptide hormones in mosquito tissues

Donna Huber on May 24, 2025

Peptide hormones in insects are primarily expressed in specialized brain, ventral nerve chord, and midgut cells. When released, peptide hormones play crucial roles in regulating physiology, reproduction, and behavior. Here, we present a protocol for detecting peptide hormones in mosquito tissues such as the brain, midgut, and hemolymph. We describe steps for tissue preparation, immunocytochemistry, fluorescent quantification, and enzyme-linked immunoassay (EIA). This protocol offers a versatile and effective approach for studying peptide hormone expression and abundance in insects. For complete details on the use and execution of this protocol, please refer to Dou et al.¹.

Xiaoyi Dou, Kangkang Chen, Mark R Brown, Michael R Strand. STAR Protoc. 2025 May 24;6(2):103850. doi: 10.1016/j.xpro.2025.103850.

A symbiotic gene stimulates aggressive behavior favoring the survival of parasitized caterpillars

Donna Huber on April 28, 2025

Animals often exhibit increased aggression in response to starvation, while parasites often manipulate host behavior. In contrast, underlying molecular mechanisms for these behavioral changes are mostly unknown. The diamondback moth, Plutella xylostella, is an agricultural pest that feeds on cruciferous plants as larvae, while Cotesia vestalis is a parasitoid wasp that parasitizes diamondback moth larvae. In this study, we determined that unparasitized diamondback moth larvae exhibit increased aggression and cannibalism when starved, while starved larvae parasitized by C. vestalis were more aggressive than unparasitized larvae. C. vestalis harbors a domesticated endogenized virus named Cotesia vestalis bracovirus (CvBV) that wasps inject into parasitized hosts. Starvation increased octopamine (OA) levels in the central nervous system (CNS) of diamondback moth larvae while a series of experiments identified a CvBV-encoded gene product named Assailant that further increased aggression in starved diamondback moth larvae. We determined that Assailant increases OA levels by activating tyramine beta-hydroxylase (PxTβh), which is a key enzyme in the OA biosynthesis pathway. Ectopic expression of assailant in Drosophila melanogaster likewise upregulated expression of DmTβh and OA, which increased aggressive behavior in male flies as measured by a well-established assay. While parasitized hosts are often thought to be at a competitive disadvantage to nonparasitized individuals, our results uncover how a parasitoid uses an endogenized virus to increase host aggression and enhance survival of offspring when competing against unparasitized hosts.

Zhiwei Wu, Xiaotong Wu, Zhizhi Wang, Xiqian Ye, Lan Pang, Yanping Wang, Yuenan Zhou, Ting Chen, Sicong Zhou, Zehua Wang, Yifeng Sheng, Qichao Zhang, Jiani Chen, Pu Tang, Xingxing Shen, Jianhua Huang, Jean-Michel Drezen, Michael R Strand, Xuexin Chen. Proc Natl Acad Sci U S A. 2025 May 6;122(18):e2422935122. doi: 10.1073/pnas.2422935122.

A myeloid differentiation-like protein in partnership with Toll5 from the pest insect Spodoptera litura senses baculovirus infection

Donna Huber on October 23, 2024

Recombinant SlML-11 slows AcMNPV infection of Sl221 cells.

Many types of viruses infect insects and other arthropods. In contrast, little is known about how arthropods sense viruses, although several innate immune pathways including Toll have antiviral functions. Large DNA viruses in the family Baculoviridae are used to control a number of pest insects. Here, we studied Spodoptera litura and Autographa californica multiple nucleopolyhedrovirus (AcMNPV) to test the hypothesis that one or more myeloid differentiation-like (ML) proteins and Toll family members sense baculoviruses. We identified 11 ML and 12 Toll genes in the S. litura genome. A series of experiments indicated that S. litura ML protein 11 (SlML-11) binds the budded form of AcMNPV and partners with S. litura Toll5 (SlToll5). SlML-11 also bound sphingomyelin (SPM), which is a component of the virion envelope. Disabling SlML-11 and SlToll5 increased susceptibility to infection, while priming larvae with SPM reduced susceptibility as measured by increased survival to the adult stage and clearance of AcMNPV from individuals that emerged as adults. We conclude that SPM is a pathogen-associated molecular pattern molecule while SlML-11 and SlToll5 interact to function as a pattern recognition receptor that senses AcMNPV.

Ruonan Zhang, Jielai Zhong, Yanjun Li, Mengge Li, Jie Zhang, Qihao Hu, Liang Wen, Xiaoxia Xu, Fengliang Jin, Wanying Yang, Yuzhen Lu, Michael R Strand, Xiao-Qiang Yu. Proc Natl Acad Sci U S A. 2024 Oct 29;121(44):e2415398121. doi: 10.1073/pnas.2415398121.

In the news: Michael Strand

Donna Huber on July 8, 2024

Michael Strand is a Regents Professor in the Department of Entomology and member of the Center for Tropical and Emerging Global Diseases. His mosquito research has recently been featured in a number of news stories.

What drives mosquitoes’ bloodlust? Their hormones (Nature)

The Science Behind What Makes Mosquitoes Bite You! Explained (News 9)

Mosquito bloodlust controlled by two hormones (The Naked Scientists)

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

Donna Huber on July 1, 2024

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

Donna Huber on April 25, 2024

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.

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