“Winter is coming.” This is the well-known motto of House Stark, one of the greatest families in the fantasy-land of Westeros, on the very popular TV series, Game of Thrones. To the Stark family, “Winter is coming” serves a call for action to prepare the people of North Westeros for the harsh cold, famished, and usually war-stricken winters of the land. The calling prepares the people of Westeros to prepare to survive through the dangerous times ahead.

“Winter is coming,” is also a message received through diapausing insects, or insects that engage in a temporary state of dormancy during unfavorable environmental conditions, such as cold winters. The Asian Tiger Mosquito engages in diapause during winter months to take time to grow and develop in an otherwise dangerous environment.

In my chosen article, “When mothers anticipate: Effects of the prediapause stage on embryo development time and of maternal photoperiod on eggs of a temperate and a tropical strains of Aedes albopictus”, the effects of photoperiod (day-length exposure) and diapause dormacy were examined on the eggs of the Asian Tiger Mosquito. The author hypothesized that inducing diapause on Aedes albopictus mothers will have effects on egg and larvae development. The article concludes that changes in photoperiod and diapause on both the eggs, larvae, and mothers of Aedes albopticus caused changes in embryonic developmental timing and egg size. 

Background info:

Diapause is defined as a hormonally-programmed physiological state of suspended development of an insect during unfavorable environmental conditions such as harsh, wintry cold. The purpose of engaging in diapause allows the Asian Tiger Mosquito to increase chances of its survival in harsh conditions. The adult mosquitoes, and eggs of these mosquitoes participate in diapause.  Egg diapause allows the Asian Tiger Mosquito larvae to hatch at a later, more environmentally favorable time. In other insects, the increased time of development allows the organism to acquire additional lipid storage, metabolism changes, and increased protein synthesis.

The ability for the Asian Tiger Mosquito to undergo diapause is in part caused by the organism’s photoperiodism. Photoperiodism is defined as the ability of an organism to determine seasonal, day-length changes and react to those changes. Being able to determine day-length changes will initiate the organisms’ ability to engage in biological events such as reproduction, dormancy, or migration. The Asian Tiger Mosquito’s photoperiod, or period time spent in illumination of the day, is crutial to its development and survival. For example, it has been observed in previous experients that larvae of Aedes albopictus take a longer time to reach developmental maturity in the absence of light exposure. 

Materials & Methods:

Two populations of A. albopictus, a diapausing temperate strain from Europe, and a non-diapausing south-east African tropical strain, were used in this experiment. The adult mosquitoes were placed in a lab room under a constant environment with a photoperiod of 16 and 8 hours of darkness. Only the diapausing temperate strain had included diapause by feeding. During egg laying, serosal cutical appearance, egg burster appearance (last morphological trait to appear), pigmented ocelli, segmentation, and egg volume of both groups were measured. The larvae and eggs of the two strains were placed in photoperiodic chambers, with non-diapausing long-day conditions (“LD”, 16 h of light, 8 h darkness) or short-day conditions (“SD”, 9h light, 15h darkness). 

Results:

The egg size of temparate, diapausing, short-day larvae mosquitoes (dark blue) was larger than othre groups:

The embryonic development of temperate, SD, diapausing group (blue) was slower than others:

Discussion:

The concluded data demonstrates the idea that diapause and short-day, temperate strains in A. albopictus will cause developmental delay in offspring and larger egg size. The reasoning behind this is to make better and bigger eggs to adequately adapt the harsh living conditions of the temperate strain. For example, the larger yolk in eggs will be able to supply the embryo with more nutrients. Thus, increasing the survival of embryos.

Maternal photoperiod has a direct influence on egg size. Long day length mosquitoes produced longer and narrower eggs that possessed changes in the outer chorion structure.

A) How do these findings apply to broader issues in science and/or the world?

By better understanding how diapause effects the Asian Tiger Mosquito, and other organisms, new developmental strategies can be implemented on mosquito population control. For example, practicing techniques that inhibit diapause in populations of these mosquitoes will lead to a lesser chance of winter survival, and in turn may lead to a decline in vector transmission of viruses through these mosquitoes.

D) What are some further experiments that would answer remaining questions?

To further study the effects of diapause and photoperiod on the Asian Tiger Mosquito and other organisms, research could be made on the molecular level. For example, genomic changes and proteomic (protein) changes within the larvae, eggs, and mother can be observed in further study to better clarify the benefits of diapause on organisms.

Citation, Link, & Info:

When mothers anticipate: Effects of the prediapause stage on embryo development time and of maternal photoperiod on eggs of a temperate and a tropical strains of Aedes albopictus (Diptera: Culicidae)

Journal of Insect Physiology: Volume 71

December 2014, Pages 87-96

Lacour, Guillaume & Vernichon, Florian & Cadilhac, Nicolas & Boyer, Sebastien & Lagneau, Christophe & Hance, Thierry. (2014). When mothers anticipate: Effects of the prediapause stage on embryo development time and of maternal photoperiod on eggs of a temperate and a tropical strains of Aedes albopictus (Diptera: Culicidae). Journal of Insect Physiology. 71. 87-96. 10.1016/j.jinsphys.2014.10.008.

Aedes albopictus is part of the family Culicidae. The first phylogenetic tree is showing the relationship of Ae. albopitcus with its other members of this family. According to the article, “The Culicidae (Diptera): a review of taxonomy, classification and phylogeny” by Ralph E. Harbach, members of the family Culicidae have been studied and organized since the beginning of binomial nomenclature, and are believed to have originated on earth in the Mesozoic era. It is, however, somewhat difficult to study extinct members of the family because fossils of these small, fragile insects are rarely preserved. Because of this lack of known physical data, much information about Aedes phylogeny is the result of DNA sequence similarities and genomic anaylses.

This first tree organizes 6 members of Culicidae together in one section based on genetic data made from these animals’ DNA. Scientists studied the sequence data for the cytochrome oxidase c subunits I and II (COI, COII) of mtDNA from these species. 

Figure 1: Phylogenetic Tree Aedes

Figure 2: Aedes. Culex. and Anophleinae

In Figure 2, Aedes albopictus is shown to be contained within a tribe called Aedini. This tribe’s contained species posses compound eyes, erect scales on head, tarsal claws, and a pointed abdomen.

In both phylogenetic trees, it appears that Aedes albopictus is a close relative of the genus Culex. In figure 2, Aedes and Culex are shown to have a common ancestor of the Anophelinae genus. These genera share common characteristics, such as similar egg shape, proboscis style, and larval form.

Figure 3: Morphological similarities between Aedes, Culex, and Anopheles

In one study, “Rapid identification of medically important mosquitoes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry,” proteins were collected from the cephalothoraxes of members of Aedes, Culex, and Anophelinae. Using a PCR technique, the study found many similar proteins contained within the bodies of these organisms. The PCR found many similar peaks within the protein analyses, which concluded that these species are similar in composition, which links the three genera to a common ancestor.

 Figure 4: PCR of Mosquito Proteins

http://mosquito-taxonomic-inventory.info/simpletaxonomy/term/8577

https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-018-2854-0#Sec18

https://www.researchgate.net/figure/Phylogenetic-tree-with-Culicidae-species-and-outgroupPhylogenetic-tree-constructed-using_fig2_323988244

Harbach, R E. “The Culicidae (Diptera): a review of taxonomy, classification and phylogeny*.” (2007).

Nobody likes a mosquito bite.  The irritation, the annoying bump, and the inability to notice when being bit is frustrating to anyone. It’s obvious to feel the results of a genus Aedes mosquito in our own bodies. However, we rarely think physiological mechanisms that these pesky mosquitoes use to – sneakily – suck our blood. Do mosquitoes use Dracula-like fangs to conduct their blood-thirsty biting sprees? What causes the irritation from the bite? How do mosquitoes carry deadly diseases from one organism to another? Biologists have conducted multiple studies to answer these question about the feeding mechanisms of the Aedes genus.

Mosquitoes from genus Aedes can drink up to three times their body weight of blood into their bodies. To do so, Aedes uses two, strong pump organs located in the head to transport the bloodmeal from the proboscis to the gut. These two pump organs, called the cibarial dilator pump (CP) and the pharyngeal dilator pump (PP), work in conjunction to help Aedes mosquitoes suck blood quickly and efficiently. The cibarial pump, located at the distal end of the proboscis, is smaller than the more deep, pharyngeal pump. The larger pharyngeal pump pushes food to esophagus. The CP and PP pumps are separated by the pharynx, which acts as a valve between the two pumps. The two balloon-like pumps are controlled by a series of muscles within the head that allow for the contraction and dilation of the organs to push blood through the head towards the esophagus, much like a bulb syringe pushes fluid. According to scientist Kenji Kikuchi, “Variation in expansion rate and volume of the pumps, combined with variation in their phasing and valving, should result in variable pressure drops, and hence differences in flow rate or blockage-clearing ability.”

The cibarial and pharyngeal pumps are shown here along with assisting muscles. The graph represent the oscillation of contraction and dilation of the pumps as the mosquito feeds.

What causes the irritation from a mosquito bite? Studies show that the cause of this irritation are the bioactive lipids and proteins contained within Aedes salivary glands. These proteins within the mosquitos’ saliva help with anticoagulation of blood, vasodilation of host blood vessels, and immunomodulators for the mosquito. When a mosquito bites, it doesn’t only suck blood; the mosquito injects saliva into the host’s skin as well. After a mosquito bite, our bodies release histamine as a response to contact of this foreign substance, swelling and itching is a result.

For years, scientists have tried to explain the transfer of infectious diseases through animal vectors like mosquitoes. A 2019 study by Valter Monterio concluded that the contents of Aedes mosquito saliva aid in blood digestion, but can also inhabit viruses, such as the deadly Chikungunya (CHIKV) Virus. Monterio states, “… mosquito saliva is an important factor in the transmission of CHIKV due to the existence of a series of substances with immunomodulatory and anticoagulants actions. These components may help the mosquito in blood ingestion, but will also allow CHIKV to escape from the host, and are thus fundamentally important to the virulence and pathogenicity of this virus.” The particular CHIKV virus is able to live throughout the mosquitos’ body, and replicates within the basil lamina of Aedes acinar cells.” These acinar cells produce mosquito saliva and make up the salivary glands of the mosquito. Unfortunately, this physiology makes mosquitoes vectors for many deadly diseases and can impact other organisms. As more studies like these occur, biologists can better determine transmission of diseases in vectors such as mosquitoes, and how to prevent transmission.

Replication of CHIKV in Aedes mosquito. The virus penetrates basal lamina of acinar cells, replicates, and is released into host via salivary ducts.

http://www.dipterajournal.com/pdf/2015/vol2issue3/PartA/2-2-29-440.pdf

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184871

Kikuchi, Kenji et al. “Burst mode pumping: A new mechanism of drinking in mosquitoes.” Scientific reports vol. 8,1 4885. 20 Mar. 2018, doi:10.1038/s41598-018-22866-w

https://books.google.com/books?id=RoIoCTSI438C&pg=PA290&lpg=PA290&dq=cibarial+pump+pharyngeal+pump+aedes&source=bl&ots=J7OYGkHiv5&sig=ACfU3U0MldCwY72TQMb2hXqxdYFrhLgbyQ&hl=en&sa=X&ved=2ahUKEwiE2LScg8DoAhVLhuAKHccBAgE4ChDoATAFegQICxAB#v=onepage&q=cibarial%20pump%20pharyngeal%20pump%20aedes&f=false

https://jvi.asm.org/content/92/12/e01004-17

Imagine a world without perception; No tasting of your favorite dish, no smelling pleasant perfume, no listening to riveting music. There wouldn’t be one! We reply our senses to perceive and survive in the world around us. Just like we, and many other organisms rely on our senses to assess our environment, so do members of the mosquito genus Aedes. Members of Aedes use unique structures called maxillary palps to perceive their outside world.

 Aedes albopticus uses structures called maxillary palps, which are located on the lateral sides of their proboscis (elongating appendage) to detect their hosts thro

Maxillary Palps are located on the proximal, lateral side of the mosquito’s proboscis.

ugh olfaction, chemoreception and thermoreception. Their maxillary palps allow the species like the Asian Tiger Mosquito to perceive temperature, certain pheromones, humidity, and mild touch. These maxillary palps aid the mosquito in host seeking, mating, and feeding.

Olfaction is achived along these maxillary palps by hair-like sensory structures called sensilla. There sensilla house olfactory receptor neurons, which allow the mosquito to have a sense of smell. In the 2017 study, “Deciphering the olfactory repertoire of the tiger mosquito Aedes albopictus”, genes contained within maxillary palps of the Asian Tiger Mosquito were studied at a microscopic level. The results found g

The sensilla are the hair-like projections shown in the photo, which arise from the maxillary palp.

ene coding for odorant receptors, ionotropic receptors, and gustatory receptors. In addition, gene material of the maxillary palps also consisted of genes involved in thermoreception, mechanosensation, and neuromodulation were found.

Using these maxillary palps, some members of the genus Aedes have evolutionarly developed a “taste” for humans. In the 2014 study, “Evolution of mosquito preference for humans linked to oderant receptor”, lab conductors studied maxillary palps of two types of mosquitoes; Aedes aegypti, and Aedes formosus.  Collected Aedes aegypti mosquitoes came from an area of East Africa that had a large human population, while the Aedes formosus were collected from a forested area with little to no human population. The results studied maxillary palps of the two species. The Aedes aegypti mosquitoes actually have evolved, “ligand-sensitivity of the odorant receptor AaegOr4, which … recognizes a compound present at high levels in human odor.” Because Aedes aegypti have been exposed to human odor more frequently, the sensilla of their maxillary palps “preferred” human scent!  Through this study, and many others like it, scientists are able to find how the use of the Aedes maxillary palps affect their behavior.

McBride C. S., Baier F., Omondi A. B., Spitzer S. A., Lutomiah J., Sang R., et al. (2014). Evolution of mosquito preference for humans linked to an odorant receptor. Nature 515, 222–227. 10.1038/nature13964 [PMC free article] [PubMed] [CrossRef] [Google Scholar]

Lombardo, F., Salvemini, M., Fiorillo, C. et al. Deciphering the olfactory repertoire of the tiger mosquito Aedes albopictus . BMC Genomics 18, 770 (2017). https://doi.org/10.1186/s12864-017-4144-1

https://www.ncbi.nlm.nih.gov/pubmed/24613607

https://www.britannica.com/animal/Aedes

http://wildpro.twycrosszoo.org/S/0zAMand_Hexapod/Dipt_Culi_Aedes/Aedes_albopictus.htm#PupaMorph