Within the family Aphididae, also known as aphids or plant lice, there are 24 subfamilies, 510 genera, and 5109 species. Aphids are very small insects that live in large colonies and feed on plant sap. Most aphids are specialized to feed on a specific type of plant, although a few species can feed on hundreds of unrelated plants. Their diversity is highest in northern temperate areas, but they have been recorded in all terrestrial habitats, excluding extremely cold regions. (Dransfield and Brightwell, 2023; Singh and Singh, 2020)
Aphids are cosmopolitan, meaning they are found in most regions of the world, excluding very cold and icy regions. Most aphids are endemic to (can only be found in) a particular region. They are most common and have the highest diversity in northern temperate areas. Although aphids are found in the tropics, their diversity in these regions is comparatively low and there are very few aphid species that are specific to tropical plants. (Dransfield and Brightwell, 2023; Singh and Singh, 2020)
Higher classification of aphids is controversial and currently unresolved. Little is known about aphid phylogeny (evolutionary history). The family Aphididae is a part of the aphid superfamily Aphidoidea, in the infraorder Aphidomorpha, suborder Sternorrhyncha, and order Hemiptera (true bugs). Historically, aphids were classified as part of the suborder Homoptera, but that suborder is now considered obsolete because scientists discovered that there is no common ancestor for all homopterans. The superfamily Aphidoidea also contains two other families: Adelgidae (adelgids) and Phylloxeridae (phylloxera). Aphididae contains about 90% of all aphid diversity. Formerly, adelgids were also considered aphids but are now classified as their own family. There are still at least 100 species in Aphidoidae that are called aphids but are not a part of the family Aphididae. (Dransfield and Brightwell, 2023; Gullan, 2001; Stoetzel, 1998; Żyła, et al., 2017)
Aphids are small insects, approximately 2 mm in length, with a range between 0.4 and 7.8 mm. Their bodies are soft and typically egg-shaped, but can be oval, flat, or elongate. Their color can be green, brown, or grey. All adults have two segmented antennae, long stylets (mouthparts), and a pair of cornicles (tubes that stick out backwards from the end of their abdomen). Aphid eggs are usually round, oval in shape, and smooth. Nymphs resemble smaller adults and are always wingless. The majority of adult aphids are also wingless. The body shape, size, and appearance of aphids can vary significantly within a species because their polymorphism. (Braendle, et al., 2006; Delahaut, 2005; Dixon, 1985; Dransfield and Brightwell, 2023)
All aphids have multiple seasonal morphs, which makes it difficult to identify them. Some species of aphids have as little as two morphs, while others have as many as twelve. The most common aphid morphs are the following: fundatrix, vivipara/aptera, male, ovipara, soldier, and alata. Because most of these morphs are seasonal, they appear at different times of the year. At the beginning of the season, in spring, the fundatrix generation appears. This morph is wingless with a round, often hairy, body. The offspring of the fundatrices can be alata, vivipara/aptera, or defensive morphs. These three morphs are present throughout spring and summer. The alata morph is female, has a smaller body, longer legs, and is winged. The vivipara/aptera morph is the most common morph. It is wingless, female, and round. The soldier morph is a nymph with thick legs. Lastly, in early fall, the sexual generation, consisting of ovipara and male morphs appears. The ovipara morph is female, has a longer body, and is wingless. The male morph is smaller, winged, and in some species does not have mouthparts. (Braendle, et al., 2006; Dixon, 1985; Dransfield and Brightwell, 2023)
The developmental patterns of aphids vary between morphs and generations, but they all have incomplete metamorphosis. The summer and fall morphs (vivipara/aptera, alata, male, and ovipara) have two life stages: nymph and adult. These aphids are born as nymphs, then molt about four times to an adult. The amount of time it takes for an aphid to mature depends on the temperature. In warm conditions, it can take as little as seven or eight days for a newborn nymph to reach adulthood. Unlike the other generations, the fundatrix generation has three life stages: egg, nymph, and adult. The egg is laid in the fall by the sexual generation and then overwinters, hatching in the spring as a nymph. From this point, the fundatrices follow the same developmental patterns as the summer and fall generations. All of the morphs described above are neotenic, meaning that they retain some juvenile traits into adulthood. Lastly, soldiers have only one life stage. They are born as a nymph and remain a nymph their entire life, although they may molt several times. (Delahaut, 2005; Flint, 2013)
Adult oviparae (sexual females) emit sex pheromones when they are sexually mature and ready to mate. The males detect these signals and use them to locate oviparae. In some species, after mating, a male may "mark" his female partner with pheromones to deter other males from mating with her. Most sexual aphids are promiscuous, meaning that both the males and females have multiple partners. Females who mate multiple times typically lay a larger number of eggs. Some female aphids have been observed showing non-cooperation when a male attempts to mate with them, but it is not known what this behavior means. Females may be non-cooperative because they are looking for a place to lay their eggs or because they are rejecting the male. (Doherty and Hales, 2002; Pettersson, 1970)
Most aphids alternate between sexual and asexual reproduction. The first generation of the season, the fundatrix generation, is entirely female, reproduces asexually through parthenogenesis/cloning, and gives birth to live young. The summer morphs (alata and vivipara/aptera) are female and reproduce the same way as the fundatrix generation. Fundatrices always reproduce on a primary host, while summer generations can reproduce on either a primary or a secondary host (if they have one). Asexual reproduction allows aphids to grow their populations extremely quickly. Some aphids can produce up to eighty offspring per week and fifteen generations in a single year. Some aphids are even known to be born already pregnant. Soldiers never reach sexual maturity and cannot reproduce. In fall, the last generation of the season, the sexual generation, is born. The sexual generation consists of both males and females (ovipara morph). As the name implies, sexual generations reproduce sexually. Sexual generations can also only be produced on primary hosts. Although it is uncommon, species that lack a primary host cannot produce a sexual generation and can only reproduce by parthenogenesis. Instead of giving birth like the other generations, sexual females lay eggs. These eggs overwinter on a perennial host and hatch in the spring as the next fundatrix generation. (Dransfield and Brightwell, 2023; Flint, 2013; Hahn, 2019; Jaouannet, et al., 2014)
Aphids do not take care of their offspring.
Aphids can live for several weeks to a month. Their lifespan is primarily limited by predation, but their lives can also be shortened by poor weather conditions, low temperatures, and poor host quality. (Adams, 2011; Cayetano, et al., 2015)
Most species of aphid live in very large groups but do not have complex social organization. Wingless aphids are mostly sedentary and stay on a single plant their entire life, though some may travel short distances on the wind to a nearby plant. Winged aphids can migrate fairly long distances. After completing their migration, winged aphids autolyse (self-digest) their wing muscles to put more energy towards reproduction. This impairs their ability to fly. In the winter, aphids overwinter as eggs. All female morphs spend most of their time feeding, while males spend the most of their time searching for a mate. (Abbot, 2009; Doherty and Hales, 2002; Dransfield and Brightwell, 2023; Stoetzel, 1998)
While the majority of aphids have little or no social organization, a few subfamilies are social. These species, as well as some non-social species produce galls, which are large, hollow growths of plant tissue. Social species use these galls as "nests," where they feed and spend the majority of their time. They also have a distinct morph, called soldiers, specialized for defending galls from predators and invading aphids. Soldiers are not present in non-social species. Galls can be either open or closed, depending on the species. Most social species create open galls, which have small holes. Soldiers use these holes to dispose of the colony's wastes, primarily honeydew. A few species induce closed galls, which are completely closed off and the enclosed aphids are isolated from the outside world. Inside of these galls, the plant absorbs the honeydew secretions through its vascular tissues. The soldiers of these species to not participate in gall cleaning. Instead, they defend the gall from predators by attacking potential invaders. (Abbot, 2009; Dransfield and Brightwell, 2023; Kutsukake, et al., 2012; Stoetzel, 1998)
Aphids communicate with chemical signals called pheromones, which they secrete out of their cornicles. They detect these signals with sensory organs on their antennae. The most well-studied aphid pheromone is an alarm signal that the aphids emit when they are under attack to warn nearby aphids of danger. (Dewhirst, et al., 2010; Pettersson, 1970; Stoetzel, 1998; Vandermoten, et al., 2012)
Aphids perceive and navigate the world through vision, touch, and smell. They primarily use these senses to help them find a good place to feed. Winged aphids usually have more developed eyes than wingless aphids. Better vision helps these winged aphids find a new host plant when they migrate. They also use their antennae to "smell" what type of plant they are on. (Dransfield and Brightwell, 2023)
Aphids are herbivores that feed exclusively on sap. They have long, puncturing mouthparts, called stylets, that they stick into the plant to get to the sap in the plant's phloem (plant vascular tissue). The aphids' stylets are very small and thin, so before they puncture a plant, they secrete a fast-hardening substance onto their stylet to give themselves an extra layer of protection. When aphids feed, they take in more sugar than they need, so they get rid of the excess by secreting a sugary substance called honeydew. Most aphids can only feed on plants from a specific family, but some species can feed on many different types of plants. Additionally, many aphid species in the subfamilies Aphidinae (the largest subfamily), Anoeciine, and Pemphigini alternate between hosts at certain times of year. The most common hosts of aphids are the following groups: Compositae (aster, daisy, composite, and sunflower family), Coniferae (conifers), Rosaceae (rose family), Poacaea (grasses), Salicaceae (willow family), and Fagaceae (oak and beech family). (Braendle, et al., 2006; Dixon, 1985; Dransfield and Brightwell, 2023; Jaouannet, et al., 2014; Mahr, 2023; Moran, 1988)
Aphids have an endosymbiotic relationship with a bacteria called Buchnera. Sap is high in sugar but low in nitrogenous compounds like amino acids, which aphids need to survive. Buchnera lives inside an aphid's body cavity, in a structure called a bacteriome, where it synthesizes amino acids, supplementing the aphid's diet. (Baumann, et al., 2006)
Aphids are prey to many animals due to their prevalence across the globe, relatively large populations, and small size. They are the primary food source for several species, including American goldfinches (Carduelis tristis) and Myzia oblongoguttata, a ladybug species. Aphids do not have many anti-predator adaptations, but most species are cryptic, meaning that they blend in with their environment. Aphids can also escape predators by dropping off of the plant as well as warn other aphids of predators using alarm pheromones. Some anti-predator traits that are present in some aphid species but not the overall aphid family are as follows: living inside of galls, producing soldiers, having ant protectors, producing a woolly wax coating, producing strong odors to deter predators, and being toxic to certain predators. (Boggs and Chatfield, 2020; Capinera, 2011; Dransfield and Brightwell, 2023; Gish, et al., 2012; Kazana, et al., 2007; Lenhart, et al., 2018; Mahr, 2023)
Some species of aphid have a mutualistic relationship with ants (Formicidae). Ants protect the aphids from predators in exchange for the sugary honeydew that the aphids secrete. Some species of ant are even known to farm aphids. These aphids are sometimes called "ant cows," because the ants "milk" them for honeydew. (Baumann, et al., 2006)
Most aphids have a commensal relationship with their host plant(s), meaning that the aphid feeds with no harm to the plant. Some species of aphid are parasitic, as they cause harm to their host plant(s) when they feed. Many of these parasitic aphids are crop pests. Individual aphids do not pose a significant threat to plants, but large infestations can be deadly. Additionally, the honeydew that aphids secrete is known to damage fruits and support the growth of sooty mold. (Delahaut, 2005; Mahr, 2023)
Insects from the families Aphidiinae (not to be confused with the aphid subfamily Aphidinae) and Aphelinus are parasites that specialize on aphids. Both of these groups inject an egg into the body of an aphid. The egg then hatches and the larva feeds upon the aphid's body from the inside out. The larva consumes almost every part of the aphid, only leaving behind the exoskeleton. These remains are known as "aphid mummies." (Beers, et al., 2010; Dransfield and Brightwell, 2023; Rakhshani and Starý, 2021)
Due to the complex and interesting lifecycle and obscure phylogeny of aphids, scientists have used them to learn more about the biology of insects and plants, effective ways to manage crop pests, and methods to resolve phylogenetic relationships. Additionally, aphids are an important part of the food chain, as they are prey to many species. By attracting their pollinator predators to plants and providing nutrients to other animals, aphids promote a healthy ecosystem, which also benefits humans. (Dransfield and Brightwell, 2023)
Approximately 250 aphid species are agricultural pests. These parasitic aphids are notorious for causing severe damage to crop plants by taking nutrients, deforming plants by inducing gall formation, and secreting honeydew, which encourages the growth of sooty mold and damages fruits. Aphids are also responsible for transmitting up to 30% of all plant viruses. Infestations often result in lower crop yield and quality, which is economically harmful to farmers. (Singh and Singh, 2021; Żyła, et al., 2017)
Unlike many other parthenogenically-reproducing animals, female aphids produce clones, meaning that they are genetically identical to their mother, daughters, and sisters. However, because aphid morphs are determined by environmental factors rather than genetics, aphids that are genetically identical can be very different in appearance. (Dransfield and Brightwell, 2023)
Avery Gibson (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
living in landscapes dominated by human agriculture.
Referring to an animal that lives in trees; tree-climbing.
reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
animals that grow in groups of the same species, often refers to animals which are not mobile, such as corals.
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
An animal that eats mainly plants or parts of plants.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.
Found in northern North America and northern Europe or Asia.
animals that live only on an island or set of islands.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
development takes place in an unfertilized egg
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
scrub forests develop in areas that experience dry seasons.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
living in cities and large towns, landscapes dominated by human structures and activity.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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