What are Aphids?
Aphids on plants are small soft-bodied piercing and sucking phloem-feeding insects (order Homoptera) from the superfamily (a taxonomic category that is above family but below order) Aphidoidea that feed on the sap and fluids of several types of plants.
They are also sometimes referred to as the plant lice, ant cow, greenfly, or blackfly in addition to being known as aphids on plants. Most individuals of aphids on plants from this species have cornicles (tube-like projections ) around the lower abdomen.
Aphids on plants are destructive crop pests that are often green or black but can be found in different colors and habitats.
Polymorphic (occurring in different forms, especially regarding species and genetic variation )traits are found in many aphids.
Life cycle of Plant Aphids
The life cycle of aphids is a rather complicated process because they have two different methods of reproduction depending on climate, and develop two types of physiological features depending on circumstances.
Wingless female aphids known as stem mothers have the ability to reproduce without fertilization, a process called parthenogenesis. This process is used for reproduction throughout the summer. These stem mothers give birth to female young called nymphs.
Stem mothers’ reproductive process is unique not just for the ability to reproduce without fertilization, but also because they give birth to live young, a process termed viviparity (retention and development of a fertile egg in the body of the parent) rather than laying eggs like regular aphids in autumn and other insects.
The just-birthed nymphs are now believed to likely already be pregnant. This adaptation allows them to also have the capability to give birth without fertilization when they mature. A process researchers have termed telescopic development.
Male aphids have no input in this process but those that later develop wings and leave their crowded parent’s plant colony will mate and colonize other plants.
Rapid reproduction multiplies the aphid offspring on the plants they colonize. This is generally what triggers some of the offspring to develop membranous wings and migrate to other plants.
Some species of aphids (about 10%) tend to alternate between two or more types of hosts (species of plants) as it suits them. Some consume a basic type of crop while others colonize and feed on a range of plant life.
Male and females develop their traits late in the summer, mate, and the female lays eggs that endure the coming winter. In tropical or other habitats with warmer climates, there may be a continuous reproductive cycle as there is no break due to cold winters.
Types of Aphids on Plants
There are roughly about four thousand species of aphids that can be found throughout the world. An estimated two hundred and fifty of them are pests of various crops and ornamental plants.
Polymorphism of adults with winged (late) and wingless (apterous) morphs and polyphenism (non-genetic occurrence of several phenotypes in a population).
Aphids can be classified based on their taxonomy where they can be grouped according to their families, sub-families, genera, and species.
An overview of most of the major species and types is as follows:
The apple aphid (Aphis pomi)
The apple aphid or Aphis pomi has a yellow-greenish hue with a dark-colored head and legs. It is known to overwinter (survive in a dormant state through the winter) in a black egg on the apple tree which is its only known host.
The apple aphid produces honeydew (a sweet sticky fluid secreted by aphids and some scale insects) as it feeds on the sap of its host plant.
These honeydew secretions that are left on parts of the plant can be unhealthy for plants due to their significant contribution to the development of sooty mold that can seriously damage crops.
The Cabbage Plant Aphid (Bevicoryne brassicae)
The cabbage aphid (Bevicoryne brassicae) is a smallish grayish-green aphid with a waxy-powdered coating. They congregate in clusters on the underside of certain crops like; cauliflower, Brussel sprouts, cabbage, etc.
It overwinters in black eggs mainly in the northern regions but manifests no sexual stage in southern regions.
The Corn Root Aphid (Anuraphis maidiradicis)
The corn root aphid is a very destructive pest that depends largely on the cornfield ant. These cornfield ants store the corn root aphid’s eggs in their (cornfield ant’s) nest over the winter period.
The adult corn root aphids are typically wingless and spherical. They are generally pale or bluish-green with black-colored heads and black or reddish eyes. The adult stage has four different forms. The male, the egg-laying female, and the winged and wingless females that give birth to live young.
The female in the egg-laying period has a gray body with a pinkish abdomen and a white powdery coating. The lengths vary with small nymphs being 0.3mm long and adults being about 2.0mm long.
The egg is dark green, elongated, oval, and less than 1mm in length. The nymph is pale green has red eyes and looks similar to the adult.
When the winter is over and spring arrives the cornfield ants carry the newly hatched aphid nymphs to roots of various plants and particularly corn roots.
The young aphid nymphs stunt the growth of corn making them wilt and assume a yellowish hue and may even die.
Green Bug Plant Aphids (Toxoptera graminum)
The green bug (Toxoptera graminum) is one of the most destructive pests of important crops such as wheat, oats, and many other small grains.
After appearing as sickly-looking yellow patches and bumpy formations on the crops it can rapidly ruin entire fields of crop.
Adults are typically a pale or faded green with a darker green marking on the back. Females are able to produce between 50 and 60 nymphs for every generation of the twenty annual generations.
Green Peach Aphid (Myzus persicae)
The green peach aphid (Myzus persicae) is also known as the spinach aphid is pale yellow with three dark lines or markings on its back. Its life cycle usually involves this aphid using two hosts.
The female reproduces parthenogenically (asexually) during the summer and in autumn produces males and females that will subsequently reproduce sexually.
The green peach aphid is known for transmitting many plant mosaic diseases.
Cotton or Melon (Aphis gossypii) Plant Aphids
The cotton or melon (Aphis gossypii) is a greenish or black aphid that has an egg stage during the winter in temperate and cold regions. In warmer or tropical regions the cotton or melon aphids will produce live young all year round.
This parasitic aphid has many hosts that it infests including melon, cotton, and cucumber.
Pea Aphid (Acyrthosiphon pisum)
The pea aphid (Acyrthosiphon pisum) is usually colored either pinkish red or pale green. It typically overwinters in alfalfa and clove plants and only migrates to peas in spring.
It is one of the main parasites responsible for transmitting the yellow bean mosaic virus which is one of the major pea plant killers.
The pea aphid females each produce between fifty to one hundred offsprings in seven to twenty generations every year. They are vulnerable to natural predators like ladybirds and susceptible to parasites like the acarid Allothrombium pulvinum.
Variations in genes that produce carotenoid pigments are responsible for the pea aphid’s color which helps it to elude certain predators and parasites.
Its ability to produce carotenoids is due to an evolutionary process termed horizontal gene transfer. This is a process where a beneficial gene, (in this case the pea-acquired carotenoid gene), is passed on through multiple generations from an ancestor’s encounter millennia or even millions of years in the past.
Energy ATP (adenosine triphosphate) generation in pea aphids has been directly linked to carotenoid production.
Potato Aphid (Macrosifum euphorbiae)
The potato aphid (Macrosifum euphorbiae) hatches from black egg vessels on rose plants into bright pink and green nymphs that relentlessly feed on the young rosebuds and leaves.
Early in spring, they migrate to potato plants which they use as their summer host. Every two to three weeks another generation occurs. They are carriers of tomato and potato mosaic virus diseases that are very damaging to blossoms and vines.
The Rose Aphid (Macrosifum rosae)
The rose aphid (Macrosifum rosae) is a large green piercing and sucking insect with black appendages and pink markings.
The rose aphid’s only known host is the cultivated rose which it either severely damages or causes the death of the rose plant. Its natural predators are the larvae of ladybirds and lacewings (aphid lions).
Rosy Apple Aphid (Dysaphis plantaginea)
The rosy apple aphid (Dysaphis plantaginea) is a small roundish shaped aphid that can be pinkish, pale red or similar colored.
Its feeding activity severely damages foilage making leaves curl up around the aphids twisted due to toxins from their saliva and deforming fruit.
Rosy apple aphids also use plantain plants as an alternate host plant during their life cycle and from there return to the apple tree in autumn to lay their eggs.
Mountain ash, pear, and hawthorn trees are also attacked by these aphids and are controlled naturally by lacewings, lady beetles, parasitic wasps, and syrphid flies.
Wooly Apple Aphid (Eriosoma lanigerum)
The wooly apple aphid (Eriosoma lanigerum) differs from other aphids in appearance, life cycle, and the overall type of damage inflicted on the tree. One of the ways it differs from other aphid parasites is that it not only attacks the upper parts of the tree but the roots as well.
The colony generates large masses of what looks like collections or heaps of cotton clustered around wounds and scars on the trunk and branches of the tree.
The aphids themselves are purplish or reddish-brown but surrounded and covered by a white thread, wool, or cotton-like secretion that conceals the actual aphids and from which the name wooly apple aphid is derived.
Wooly apple aphids weaken and sometimes kill the tree by feeding on the branches, stem, and most destructively, the roots. Young apple trees are particularly vulnerable because they’re not yet strong enough to withstand such damage.
Strands of long white waxy substances are secreted that further protect the aphids from pesticides and predators. They also produce honeydew which causes further problems from the black sooty mold that is generated by it.
The Black Bean Aphid
The black bean aphid on plants (Aphis fabae) is a small black insect of the Hemiptera order and Aphis genus. Common names include beet leaf aphid, blackfly, and bean aphid.
It is a parasite of various agricultural crops and ornamental plants during the warm summer months. They are all winged and wingless females during this period.
They are notorious for feeding on and destroying many crops particularly beans and cause similar problems as other destructive aphids other than the direct damage to plants like the sooty mold from the honeydew generated.
Genus Hyalopterus (Aphidini)
These aphids range from small to medium in overall size and have elongated bodies. The adults are viviparae and may either be winged or wingless.
The Hyalopterus aphids are usually a pale green hue mottled with darker green areas and covered with a waxy secretion. Some of the aphids that are on their summer host may have a dark pink hue rather than the usual green.
Their antennae are shorter than their body length and the siphunculi are short, thick, and darker towards the tips with a cauda that is notably longer than the siphunculi.
This is a small genus that has only three species. They are not attended by ants and may retain a sexual stage in their life cycle.
They alternate hosts between the plum (Prunus spp) in the winter/spring and common reed (Phragmites) in summer or may decide to live on any of the hosts all year.
A member of this group is a major pest of plum trees where the honeydew generated by the aphid’s feeding activity coats the leaves and gives rise to a destructive fungus.
Grouping of Aphids based on Color
Aphids can simply be grouped based on their color. Their appearance simply helps in their identification but does not properly classify each one. Based on their color they could be grouped as white, red, green, yellow, purple, black, etc.
White aphids are those aphids that appear to be white or have whitish colorization on or around their bodies on casual inspection or observation from a slight distance.
This description is not based on binomial nomenclature but informal layman’s term or plain English. Unlike some species of whiteflies, the white aphid is not actually white but though they may sometimes appear to be.
There are three fundamental reasons why some species of aphid appear to be white. They are as follows:
- Moulted Exoskeleton: When some aphids molt and acquire a new shell, the discarded exoskeleton is sometimes white. This leads to them being sometimes described as being white.
- Wooly Cotton-like secretions: There are some species of aphids like the wooly aphid (Eriosoma lanigerum), that have a thick wooly cotton-like secretion that covers their colony and helps protect them. This wooly covering is typically white and may give the impression that the actual aphids themselves are also white whereas they are colored differently.
- Some species of aphids bear young nymphs that have whitish bodies that are usually tinged or tinted with some other color like pink, yellow, green, purple, or red, etc. These nymphs can look white when looked at briefly, from a distance, or at a glance.
Examples of Aphids that appear to be white due to pale hues or secretions:
- Eriosoma lanigerum
- Dysaphis plantaginea
- Brevicoryne brassicae
- Cryptomyzus ribis
- Euceraphis betulae
- Euceraphis punctipennis
- Myzocallis coryli
- Phyllaphis fagi
Green aphid is the plain English term or layman’s term that is ascribed to aphids that have a green color. Green seems to be the most common color that aphids tend to have. Many species of aphids are either one shade of green or the other as adults or as nymphs.
The green peach aphid is taxonomically named and starts life as a green nymph but soon develops into a more yellowish hue.
There are a great number of different types and species of aphids that have green colorizations. These are a few of them below:
- Hyalopteroides humilis
- Hyalopterus pruni
- Hyperomyzus lactucae
- Macrosiphum euphorbiellum
- Macrosiphum euphorbiae
- Macrosiphum rosae
- Metopolophium dirhodum
- Microlophium carnosum
- Periphyllus acericola
- Phorodon humuli
Generally, the term black aphid is applied to any aphid that has a black-colored outer body regardless of its taxonomic nomenclature.
Incidentally, many species of aphids are colored black either permanently or at one stage of their life cycle.
The Cooly Spruce Gall Adelgid (Adelges cooleyi)
The cooly spruce gall adelgid (Adelges cooleyi) is an aphid that causes cone-like galls (about 7cm/3 inches) to form on the tips of spruce twigs.
When the galls open towards the middle of summer, adults migrate to Douglas Fir trees (Pseudotsuga menziesii) to lay eggs. The cooly’s life cycle however continues on either the spruce or the Douglas Fir.
The Eastern Spruce Gall Adelgid (Adelges abietis)
Just like its close relative the cooly spruce gall adelgid (Adelges cooleyi), the eastern spruce gall adelgid (Adelges abietis) also generates galls that are smaller than that of its counterpart at between 1 to 2.5cm (0.4 to 1 inch) and shaped like pineapples.
These galls in the plant consist of several cells with each gall containing about twelve aphid nymphs. The galls split around midsummer releasing adult nymphs that may immediately attack the same plant or other spruce trees around.
Newly formed galls are green with red or purple markings on them whereas old ones are brown or brownish. Infested branches usually die off though some hardy branches and plants are able to survive some levels of infestation.
These are middle-sized aphids that may be winged or wingless. The wingless adults may either be gray or greenish-gray with a dark sclerotic (unusually hardening of body tissue) dorsal abdominal plate.
The winged counterpart has a characteristic dark posterodorsal abdominal patch, a white patch, and a large black pterostigmal (a group of specialized cells in the outer wings of some insects) spot on the forewing.
Young nymphs typically have a white or cream hue. Roughly twenty-four species in North America, Europe, and eastern Asia. Some species of these aphids alternate between hosts of dogwood (Cornaceae) to the roots of grass (Poaceae).
The oviparae (females that produce eggs rather than live young) lay their eggs in the bark of the selected tree trunk. Some other species live on the roots of grass (Poaceae) or sedges (Cyperaceae) all year round.
Genus Aphis (Aphidini)
This species ranges from very small individuals to large aphids. Adult viviparae (female aphids that give birth to live young) may either be winged or wingless.
Their bodies typically have a broad and oval shape that has never been observed to be very elongated but is usually stout. The dorsal cuticle is membranous with a variable amount of dark sclerotic (hardened body tissue) marks.
The siphunculi (structures located on the dorsum of the sixth abdominal segment of aphids) are generally cylindrical or sometimes tapering but not swollen. The cauda (a short tail-like appendage) is usually elongated and the legs may be pigmented variably but not usually darkly.
There are about five hundred species that infest a great variety of hosts with some of them being strictly host-specific and others being found on several different species of plants but never on sedges (Cyperaceae) and very rarely on grass (Poaceae).
Several species from this group alternate hosts and many are ant-attended. Most species retain a sexual stage in their life cycle while others reproduce viviparously (birthing live young) all year round.
An aphid egg is an organic vessel or container that contains, nourishes, and protects the zygote in which an embryo of an aphid develops in the initial growth stages until it can survive on its own.
Although most individual aphids are generally parthenogenic (giving birth to live young without fertilization), most of them have the ability to lay fertilized eggs.
Adelgids and Phylloxerids lay eggs produced both sexually and parthenogenically however eggs of true aphids can only be laid by females that have had sexual contact.
The fertilized eggs are smaller than the parthenogenic eggs of true aphids which develop into first viviparously born instar-nymphs. Ovipara are female aphids that mate and lay eggs. The vivipara give birth to live young.
Some aphids only lay eggs in areas that have cold winters and the eggs can survive the winter. The egg capsules are well insulated and padded to be able to withstand low temperatures and other environmental influences.
A few aphid species have not been found to develop individuals that undergo sexual reproduction and therefore are not known to lay eggs.
Examples of such aphids on plants include Myzus ascalonicus, Neotoxoptera formosana, and Myzus antirrhinii. Myzus ornatus which is widespread in its overall distribution is generally included in this category though it has not been confirmed if it applies to members that inhabit the Himalayas.
Aphid eggs come in a wide range of colors, shapes, and sizes depending on specific species but are not generally used to identify the types of aphids.
There is not a significant amount of aphid egg-centered terminology due to their minimal contribution so far to aphid taxonomy (branch of science concerned with classification particularly of organisms and systematics).
Aphid Egg Morphology
Aphid eggs range in shape from elliptical (elongated) to chisel, and rounded forms. They may be attached to parts of the host plant with adhesive substances in clusters or individually, to thread-like and stringy materials hanging from a branch or leaf, or concealed in wooly material.
Eggs that are freshly laid tend to have a light coloring and become darker the longer they are exposed to the atmosphere.
The eggs may vary in color and shape and some species are covered in a waxy secretion that may be distasteful to some potential predators.
The colors are generally cryptic having a range of different colors that are hard to rationalize since they do not necessarily reflect the use of camouflage.
Some aphids lay their eggs in crevices in the plant body that may be close to an easy source of food. While some deposit their eggs in an area away from food sources.
Aphids on plants and their eggs have substances in their bodily fluids that can be described as freeze-resistant or antifreeze. However, the eggs have a higher resistance to cold conditions and are biologically timed to be laid at the start of winter.
Certain aphids that reproduce parthenogenically have been known to still give some level of care to their young nymphs but egg-laying aphids are not known to care for their eggs after laying.
Egg survival is therefore not guaranteed and many get consumed or destroyed by predators or damaged by the parent itself and sometimes by tending ants, other animals, or organisms like fungi.
Some sick or injured aphids on plants have even been observed laying eggs in atypical areas where their chances of survival are much lower due to their exposure to the elements, the hazard of plant traffic, and potential predators.
Aphids and Ants
Aphids and ants can frequently be observed together on plants with no evident aggression toward one another.
Some species of ants have developed a relationship with aphids of mutualism where they benefit from each other.
The ants protect and even groom the aphids and in many instances their eggs and in turn harvest the honeydew that is produced from the pressurized phloem plant sap that is forced through the alimentary canal of the aphid.
This type of relationship is termed mutualistic trophobiosis.
This action is sometimes referred to as milking because the ants sometimes use their antennae to stroke the aphids to secrete the honeydew.
Some aphid farming ants even take aphid eggs to their nests and store them over winter.
Damage that aphids inflict on plants as mentioned above can range from negligible in the case of a well-developed and mature plant with a light infestation.
To crippling damage with compromised productivity and even death of the plant in cases of heavy infestation especially in young, not well-developed plants.
Signs of aphid Damage on Plants
Evidence of infestation and damage to plants by aphids include:
- Seeing the aphid parasites themselves on close observation of the plants.
- Curled up leaves
- Sickly and yellowish-looking leaves.
- Wilting leaves stems or shoots.
- Gall swellings on stems, trunks, branches, or leaves.
- Reduced or ceased productivity.
- Clusters of wooly or cotton-like materials on parts of the plant.
- Discolorization of parts of the plant.
- Stunted development.
- Presence of sticky (honeydew) or waxy (secretions) substances on the plant.
- Presence of sooty mold
- Deformed or diseased-looking fruit
The best way to avoid parasite infestation is prevention. However, when parasites have already begun attacking important crops or prevention measures prove ineffective, control measures have to be undertaken.
How to Get Rid of Aphids
The survival and productivity of plants depend on them being free from destructive pests like aphids. There are several different approaches to getting rid of aphids on plants.
Here are a few effective ways of eliminating aphids on plants.
Inorganic Ways of Getting rid of Aphids on Plants
- Use of Pesticides: Suitable pesticides can be applied with particular care with young plants and the stipulated concentration.
- Use of Soap: A mild solution of regular soap can be used for aphids control. Soapy water can be wiped or sprayed on the affected parts of the plant and this helps to control aphids.
- Insecticidal Soap: this comes as a liquid that can be diluted and applied to the affected parts of the plants.
- Use of Alcohol: Alcohol like isopropyl (isopropanol or rubbing alcohol) is also effective against aphids on plants but must be used carefully testing the mixture on small areas during a cool time of day and observing for any adverse effect on the plant.
Organic Ways of Getting rid of Aphids on Plants
- Use of Water: Spraying water with suitable pressure from a hose directly on the aphids and their eggs pushes them off the plants.
- Flour application: Flour can be applied to the plant to deter the aphids as it interferes with their direct contact with the plant surface and it also constipates them as they ingest it.
- Spraying Neem Oil: Neem oil is a very efficacious extract from the neem tree that has properties that have antimicrobial compounds that are effective against not only the parasitic aphids on plants but the sooty mold that is generated from the honeydew produced by their actions.
- Horticultural Oils: Certain horticultural oils are also effective against aphids on plants.
- Use of Cayenne Pepper: Cayenne pepper has also been found to have a preventive effect against some parasites like aphids on plants. Especially when used in a soapy water solution.
- Use of Beneficial Insects: Beneficial insects like the hoverfly, parasitic wasps, ladybugs, lacewings, etc are very effective in getting rid of insect parasites like aphids.
- Use of Diatomaceous earth (DE): Diatomaceous earth is a non-toxic organically derived substance that effectively kills aphids but should not be applied when plants are in bloom. It is harmful to pollinators like bees.
Prevention, they say is better than cure and this applies to aphids on plants as well. There are simple but effective ways of keeping these parasites away from crops.
How To Prevent Aphids
There are safe organic-based methods of preventing infestation of aphids on plants. The main ways are as follows:
Dormant Horticultural Oil
Dormant horticultural oil can be sprayed on fruit and shade trees to kill any overwintering aphid eggs.
The introduction of beneficial insects like lacewings, ladybugs, and parasitic wasps that feed on aphids will keep them from thriving. These insects can be encouraged to visit or take up residence in the targeted habitat in three ways:
- Cultivating plants that those insects are attracted to.
- Building suitable dwellings for the beneficial insects with household and garden materials.
- Purchasing beneficial insects and introducing them directly.
Cultivating plants that repel aphids that can be planted alongside the crops that need protection. Aphids are repelled by; catnip, garlic, and chives.
Cultivating other plants with less economic value but that aphids are attracted to can trap them and keep them off the important crops. Examples of these are; mustard and nasturtium.