Mosquitoes are notorious for their blood-sucking habits, but this reputation applies only to female mosquitoes. Male mosquitoes have a completely different diet, playing a unique and important role in the ecosystem. The male mosquito's diet is primarily vegetarian, consisting of nectar, pollen, honeydew, plant sap, and the juices of rotting fruit. This article explores the diet of male mosquitoes, their ecological importance, and how they differ from their female counterparts.
The Male Mosquito Diet: A Vegetarian Delight
So, if they don't bite people and suck their blood, what do male mosquitoes eat? The male mosquito's diet is primarily made up of the pollen and nectar of flowers. In fact, male mosquitoes are pollinators! They also feed on honeydew, a sugary substance secreted by sap-sucking insects like whiteflies, aphids, and scale insects. This peaceful, non-violent male mosquito diet provides all the nutrients these gentle insects require to thrive.
Nectar and Plant Sugars: The Primary Food Source
Male mosquitoes primarily feed on nectar and other plant sugars. This diet provides them with the necessary energy to survive and fulfill their role in the ecosystem. They are attracted to flowers and plants that produce nectar. By feeding on these sugary substances, male mosquitoes contribute to the pollination of various plants.
Honeydew: An Additional Source of Nutrition
In addition to nectar, male mosquitoes may also feed on honeydew, a sugary substance excreted by aphids and other plant-sucking insects. Honeydew provides an accessible and rich source of carbohydrates for male mosquitoes.
The Role of Male Mosquitoes in the Ecosystem
Because the male mosquito's diet does not include blood and they never bite people, some consider them harmless insects serving their own purpose in nature.
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Pollination: Supporting Plant Reproduction
Adhering to a male mosquito diet includes feeding on flowers. Male mosquitoes spread pollen from one bloom to another, working as pollinators. While male mosquitoes are not as efficient as bees, they still play a role in pollinating plants. As they feed on nectar, they inadvertently transfer pollen from one flower to another, aiding in the reproductive process of plants. This pollination contributes to the health and biodiversity of ecosystems, supporting various plant species.
Food Source: Sustaining Predators
Male mosquitoes have an additional role to play in any ecosystem they inhabit: prey. Male mosquitoes serve as a food source for various predators, including birds, bats, dragonflies, and spiders. Their presence in the food chain supports the diet of these predators and helps maintain ecological balance. By being a part of the food web, male mosquitoes contribute to the overall health and stability of their ecosystems.
Differences Between Male and Female Mosquitoes
Learning the answer to "What do male mosquitoes eat?" is what brought you here, but stick around for some additional cool male mosquito facts!
Mouthparts: Adapted for Different Diets
Male mosquitoes have mouthparts designed for feeding on nectar and plant sugars. They do not have the specialized mouthparts required for piercing skin and sucking blood. Female mosquitoes, on the other hand, are equipped with specialized mouthparts to pierce skin and feed on blood, which provides the necessary proteins for egg development.
Lifespan: Varying Roles in Reproduction
Male mosquitoes generally have a shorter lifespan than females, living for about a week. Their primary role is to mate with females. Female mosquitoes live longer, up to several weeks, as they need to find blood meals and lay eggs.
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Male Mosquito Facts
For instance, did you know there are billions and billions of mosquitoes worldwide? Male mosquitoes don't transmit disease. Male Mosquitoes are the first to hatch. Male mosquitoes have sensory superpowers. They have highly sensitive antennae tuned to detect the wingbeat frequency of female mosquitoes. Male mosquitoes are sneaky sugar thieves. We've already debunked common myths about male mosquitoes biting people or having no role in the ecosystem.
Blood Feeding by Male Mosquitoes: An Unexpected Discovery
Blood- and sugar feeding of female mosquitoes has been frequently observed in the laboratory and in the field, but only sugar feeding of males has been reported. Here, we describe for the first time that Culex quinquefasciatus males feed on blood as well. Blood feeding easily happened on a blood-soaked cotton roll and, to a lesser extent, through a thin artificial layer. Mating history of a male specimen does not affect his blood feeding behavior. Male mosquitoes feed on blood even when they have a readily available sugar source. Nevertheless, feeding on blood reduces the survival rate of males to just a few days, as compared to more than a month for mosquitoes fed only on sugar. Comparing survival of male mosquitoes fed on blood only, sugar only, and a combination of both clearly demonstrated that mortality is not affected by malnutrition (reduced sugar levels), but rather due to ingested blood. On average male mosquitoes ingested ca. 0.5 μl of blood, i.e., about 10% of the amount of blood ingested by an engorged female. Although this unexpected observation of blood feeding in the laboratory by male mosquitoes is interesting, structural impairment prevents male feeding on vertebrate blood.
Experimental Setup
Cx. quinquefasciatus mosquitoes used in this study originated from a stock laboratory colony, which in turn started from adult mosquitoes collected in Merced, CA in the 1950s and is maintained by Dr. Anthon Cornel in the Kearney Agricultural Center, University of California. In Davis, mosquitoes were maintained in an Environmental Walk-in Room (Darwin Chambers Company, St. Louis, MO, USA) at 27 ± 1°C, under a photoperiod of 12:12 h (L:D) and relative humidity (RH) of 75% for the last 5 years. Adults were maintained in 30 × 30 × 30 cm aluminum collapsible cages (BioQuip, Rancho Dominguez, CA, USA), covered by dark green, UV-resistant polyester netting (24 × 20 mesh), and had continuous access to water and 10% (w/v) sucrose-soaked cotton rolls. (local time zone), respectively. Each cage received defibrinated sheep blood on two consecutive days using an artificial feeding apparatus. Blood was provided by the University of California, Davis, Biological Media Services, Cat # 4024. An ovicup was placed in each cage 4 days after the second blood meal. Eggs were laid in half-filled water dishes (110 ml polypropylene containers, Falcon 354014) and hatched a day later. Groups of 175 first-instar larvae were transferred to clear plastic pans (32 × 17.5 × 11 cm) and fed with the powdered Tetramin® fish food until pupation. Larvae received 70 mg of food in the first 5 days, followed by 105 mg in the following days. Four-day-old male individuals of the same cohort, who had continuous access to water and sugar solution were used in assays of this study. Mosquitoes were picked with a mouth aspirator and released in a clear plastic cup (900 ml, 11 cm diameter on top), which had two screened slots (5 × 5 cm) on either side. Mosquitoes fed through a 1.5 cm opening, i.e., approximately the same diameter of a test tube, on the cup's lid. Test tubes filled with water, sugar, or blood were blocked at the open end with cotton rolls, and were inserted into the lid's opening until 3 cm of the test tube protruded inside the plastic cup (Figure S1). To provide virgin males, i.e., mosquitoes that never met mosquitoes of the opposite sex, pupae were collected and individually placed in test tubes. After emergence, males were transferred to cups, whereas mated males were collected from our rearing cages soon after mating.
Survival on Sucrose Solutions
Survival ratio of males is much higher on all sucrose solutions (over 40 days) than on water (less than 5 days; Figure 2A). Since when we first observed blood feeding by males we did not know the mating status of those individuals, we then compared the effect of blood feeding on survival of mated vs. unmated males…
Mating and Blood Feeding
Working with virgin males and females in a clear plastic cup, we observed male blood feeding for the first time. Therefore, one initial question was whether blood feeding in males is somehow connected to their mating background. In order to address this question, an experiment was designed to measure male blood feeding in mated and unmated male mosquitoes. Mated males with access to only sugar or blood were compared to unmated males, with similar access to sugar and blood. Six male specimens were released in each cup and mortality was recorded for 10 days for four replicates (n = 4). All males used in this experiment had already been proven to feed on a dyed sucrose solution for the first 4 days after their emergence. Picking sugar-fed males was easily possible by observing the green dye in their midgut. This way we were ensured that the males used had already fed on sugar and did not suffer from starvation before the experiment began. Blood, sugar, test tubes, and cotton rolls were replaced every other day, and data were collected every day.
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Dye Effects on Survival
Hunt Valley, MD, USA) added to the sugar solution was tested vs. the same solution with no dye in order to find out if there was any effect of such a dye on male survival. This dye contains water, propylene glycol, FD&C yellow 5 and blue 1, propylparaben. To determine a possible negative effect of blood meal on male mosquito survival, we prepared six plastic cups, each containing 10 male specimens. Cups were supplied with water (negative control); blood (negative control); 10% sucrose, (positive control, S10%); 10% sugar, 10% blood (S10%B10%); 10% sugar, 20% blood (S10%B20%), and 10% Sugar, 40% blood (S10%B40%).
Feeding Preference
To determine male feeding preference (blood vs. sugar), we either used a plastic cup or a rearing cage. If a plastic cup was used, 20 mosquitoes were released into the cup, and two test tubes, containing sugar and blood, were supplied to them (mounted on top, 4.5 cm apart; Figure S2A). For a dual choice cage assay, 20 male specimens were released in the cage and the same sugar and blood tubes were hung at the two opposite corners inside the cage (30 cm apart; Figure S2B). Blood-impregnated cotton rolls used in these assays were not heated, and offered to the males at room temperature. Males were starved for 12 h prior to the experiments.
Membrane Feeding
In order to research whether male mosquitoes are able to penetrate an artificial membrane and get the blood in a manner similar to females, a simple blood feeding apparatus was designed. A 100 ml Schott bottle (Duran, Germany), filled with room temperature water to increase stability, was turned upside down and 0.3 ml blood was poured on the bottom. The blood-filled concave bottom was then covered with a stretched layer of Parafilm (Figure S3A). Our observational cage was in fact a normal rearing cage, whose net was removed and replaced by a transparent food wrap layer at four sides (ClingWrap, Glad Products Co., Oakland, CA, USA). One side of the cage was covered with a sheet of white paper to provide a good background for observation and the top was covered with a piece of white net. Mosquitoes were released into the cage and the blood feeding apparatus was placed on the net (Figure S3B).
Blood Meal Volume Determination
Due to the toxicity of conventional cyanohaemoglobin protocols, blood meal volumes were determined using a modified alkaline haematin method, originally derived from Zander et al. (1989). Our adaptation of this method requires that blood is dissolved in a solution of 0.1 N NaOH (Fisher Scientific #: S318-500) and 0.04 M Triton X-100 (Fisher Biotech, CAS # 9002-93-1), hereafter referred to as the alkaline haematin detergent (AHD) reagent. The AHD reagent converts hemoglobin to alkaline haematin D-575, a stable end product with a strong absorbance peak at 575 nm. In this assay, absorbance at 575 nm is proportional to total hemoglobin content between 0 and 7 μl of blood. By this method, unknown blood meal volumes can be estimated by interpolating from a previously generated standard curve. Because of the relatively small blood meal volume from each mosquito, ingested blood volumes were assessed by taking the average blood meal from five mosquito abdomens for each replicate. Either blood fed or non-blood fed mosquito abdomens were dissected under a Zeiss Stemi DV4 stereomicroscope and immediately transferred into a solution of 500 μl AHD reagent in a 1.5 ml microcentrifuge tube (USA Scientific # 1415-9100). For abdomens used in the standard curve, the known volume of blood was added immediately after dissecting the fifth abdomen. After five such abdomens were collected, they were homogenized using a tight fitting microtube pestle (USA Scientific # 1415-5390). In order to estimate blood meal volume, a standard curve was prepared with known volumes of defibrinated sheep blood (0, 1.25, 2.5, 3.75, 5, 7.5, or 10 μl for males and 0, 5, 10, 20, 25, 30, or 35 μl for females) and five non-blood fed male or female abdomens. These volumes gave an average volume of 0, 0.25, 0.5, 0.75, 1, 1.5, or 2 μl and 0, 1, 2, 3, 4, 5, 6, or 7 μl for each male or female mosquito abdomen, respectively. After homogenization, the mixtures were centrifuged at 20,000 × g for 5 min. The diluted supernatant was then filtered through a 13 mm 0.2 μM syringe filter (Thermo Fisher Nalgene # 720-1320) to eliminate calculated absorbance due to the light scattering. The filtrate was placed into 1 cm pathlength acrylic cuvettes (Sarstedt # 67.740) and absorbance was measured and recorded at 575 nm. Each known volume on the standard curve was calculated by taking the average of three replicates, each consisting of a known volume of blood homogenized with five mosquito abdomens for both males (y = 0.547x, R2 = 0.989) and females (y = 0.0448x, R2 = 0.993), respectively. Blood meal determination for blood fed mosquitoes followed the above protocol, with the exception that no blood was added after dissection. Mosquitoes were collected immediately after blood feeding and dissected or placed on ice to prevent blood deterioration.
Proboscis Measurements
In order to compare male and female structures, proboscises of both sexes were dissected under a Leica stereo microscope MS5, equipped with an ocular micrometer. Mosquitoes were placed in a glass Petri dish (10 cm diameter), and the mouth parts immersed in a tiny droplet of 1% dimethyl sulfoxide (DMSO) solution to reduce evaporation. Dissection was done with insect pins size 000 (BioQuip) and fine dissecting 5 SA VOMM tweezers (Germany). The length of the proboscis was measured for randomly picked male and female mosquitoes (n = 30, for each group). In order to normalize the distribution of our data from two-choice behavioral assays (herein referred to as groups “a” and “b”), data in each of those two groups were transformed by arc sin √a/(a+b) and arc sin √b/(a+b), respectively, and their percentiles were calculated. This transformation enabled us to use the parametric t-test for comparing the behavior of groups “a” and “b.” The distributions of transformed data were verified by a Shapiro-Wilk test for normality at P > 0.05, followed by a paired-comparisons t-test. Significant differences between several experimental groups were tested by ANOVA, and significantly different groups were recognized by a Waller-Duncan post-hoc test. Survival curves were constructed using Kaplan-Meier and analyzed using ANOVA test. All analyses were performed with SPSS statistical package Ver. 16.00 (Chicago, Illinois, USA) and graphics were generated by GraphPad Prism 6 (La Jolla, CA).
Observations
Blood feeding of male individuals was first observed when females Cx. quinquefasciatus were placed along with males in a clear plastic cup for feeding. We noticed that not only females, but also males fed on blood. This feeding easily happened on a blood-soaked cotton roll, hanged in a cup or a cage (typically 20-40% of males fed within 30 min; Figure 1A) and, to a lesser extent, through a layer of Parafilm® (Figure 1B). In marked contrast, for any single membrane feeding observation trial, no more than 5 out of 200 male individuals fed through the membrane. We noticed, however, that blood-fed males did not survive for too long. We then designed a series of experiments to test feeding preference, effect of mating on blood feeding, and effect of blood feeding on male survival. First, we compared male survival on various concentrations of sucrose solutions to provide a baseline for subsequent studies.
Mosquitoes: More Than Just Bloodsuckers
Mosquitoes have earned a reputation for being blood-suckers or ectoparasites (i.e., insects that visit hosts and attach themselves to the hosts' bodies to feed), but these insects are no vampires. Mosquitoes are primarily vegetarians, and they only occasionally indulge in carnivorous cravings. To understand why, we need to know precisely what mosquitoes eat and how a mosquito's diet changes as they mature.
The Mosquito Food Pyramid: A Stage-by-Stage Diet
The beginning of the mosquito food pyramidWhat mosquitoes eat can vary based on their stage of life. All mosquitoes begin life as larvae hatched from eggs. Their eggs are laid on the surface of or near a body of water. These baby mosquitoes thrive just under the water's surface and feed on algae, which form the foundation of the mosquito's food pyramid. Once they leave the larval stage through molts-phases in which they shed their skins-mosquitoes become pupae. Mosquito pupae do not feed at all. Instead, all of their fuel for this stage of life must be acquired during the larval stage. Eventually, the pupae rise to the water's surface, sprout wings, and become the adult mosquitoes we're all familiar with. At this stage, the mosquito's diet becomes broader rather than narrow. Why? It all comes down to the difference between what male mosquitos eat and what female mosquitoes eat.
Why Only Female Mosquitoes Drink Blood
Like butterflies, bees, and many other insects, all male and female mosquitoes have a nutritional need for sugar, which can be supplied by the nectar of flowering plants. However, once they reach adulthood, female mosquitoes are ready to breed and lay eggs. To do this, they require protein and lipids-both of which are found in the blood of other animals. Meanwhile, male mosquitoes still need the sugar meals.
Mosquitoes and Disease Transmission
Mosquitoes are among the most notorious vectors of human diseases as females feed on vertebrate blood for survival and reproduction and unwittingly transmit the protozoan parasites causing malaria and many viruses that cause infections, such as dengue, yellow fever, chikungunya, and encephalitis (Leal, 2014). They destroy more lives on a year basis than war, terrorism, gun violence, and other maladies combined (Leal, 2014). Malaria alone is responsible for 627,000 cases of death annually in the world (Anonymous, 2014). Males are accomplices in this warfare by helping making more mosquitoes, but all known mosquito-borne pathogens are harbored and amplified in female mosquitoes. In general, females of most mosquito vectors need at least one blood meal before they can lay fertilized eggs, and this trait in turn enables them to transfer viral or protozoan infection to their vertebrate hosts (Kelly and Edman, 1992). In nature, females feed on both blood and sugar depending on their availability (Foster, 1995). A sugar meal provides females with enough energy to serve their physiological needs, i.e., it sustains females until they find their hosts and allows an infected mosquito to live long enough to oviposit, bite repeatedly, and to become infective (Van Handel, 1984). It is well-known that male mosquitoes acquire their required energy from natural sources of sugar, i.e., plant nectar, honeydew, extrafloral nectaries, and rotten fruits (Van Handel, 1984; Foster, 1995) and that males do not feed on blood (Matheson, 1944; Van Handel, 1984; Ribeiro, 1987; Grant et al., 1995; Klowden, 1995; Ribeiro et al., 2001; Wahid et al., 2003).
Mosquitoes Feeding on Animals
A female mosquito ready to lay eggs doesn't need to feed exclusively on human blood. Birds, like crows, jays, robins, and sparrows, must also fend off biting mosquitoes. The same goes for waterfowl, such as ducks, geese, and herons. Outside of the bird kingdom, small mammals such as raccoons have a place in the mosquito's diet, as do some snakes, lizards, frogs, and fish.
Why Mosquitoes Bite Humans
As we know, what mosquitoes eat depends on their species. While some mosquito species, like the tiger mosquito, prefer to drink human blood, the real reason mosquitoes bite humans is that they often present as the most attractive target when their preferred food source is in short supply. Mosquitoes are alerted to the presence of a nearby food source by a number of factors, including movement, smell, the source's carbon dioxide (CO2) emissions, and much more. The average human being exhales more CO2 than, say, a squirrel and makes a more significant blip on the hungry female mosquito's radar and an easier overall target. The human body also features odor‐producing chemicals that, while unpleasant or undetectable to us, make the female mosquito's mouth water.
Mosquitoes and Survival
A mosquito's diet typically allows it to survive for several days without food, but the exact amount of time can vary depending on the species, temperature, and humidity. Female mosquitoes require a blood meal in order to lay eggs, while male mosquitoes primarily feed on nectar. Mosquitoes feed multiple times during their lifespan, with some species requiring one blood meal per egg-laying cycle and others requiring multiple blood meals.