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TaxonomyA family (Aphididae) of small insects ((~4,400 species), in the suborder Sternorrhyncha, that suck the juices of plants. Important genera include Schizaphis and Myzus.
Aphids in North AmericaThe combined effects of global warming, the increase in international trade and traveling and habitat modification increase the probability of introducing new specis. For example, 261 (18%) of the 1,15 aphid species present in North America are concidered to be exotic. Europ is the leading source of introduced species (63%)., whereas tropical and subtropical aphid species currently make up a minority of the exotic species in North America. Among the 261 exotic species in North America, 3% are considered to be potential pests, with 18% being considered highly damaging pests.
Economic importanceAphids may cause losses of up to 30% in crops. Moreover, they are efficient vectors of hundreds of viral diseases in plants. For example, potato leaf roll virus (PLRV) and potato virus Y (PVY) by the peach-potato aphid M. persicae and barley yellow dwarf virus (BYDV) by the grain aphid S. avenae.
EnemiesMany organisms, including entomopathogenous fungi, predators or parasites, use aphids as resources. Best known aphid predators are ladybugs, for example, Coccinella septempunctata (seven-spotted ladybug or C-7). Parasites of aphids are mostly endoparasitoid insects, i.e. insects which lay eggs inside the body of an other insect which will die as a result of their development. In this article, we review the consequences of the numerous pecularities of aphid biology and ecology for their endoparasitoids, notably the Aphidiinae (Hymenoptera: Braconidae).
EndosymbiontsAphids provide exellent model for maternally transmitted symbionts. The primary symbionts, Buchnera aphidicola, inhabits specialized cells (bacteriocytes), and is required for host development, growth and reproduction.
Brief facts: pea aphid (Acyrthosiphon pisum)
Host plantsIn comparison to many other aphid species that are entirely host specific, the pea aphid is found on a few different families of plants which are the alfalfas, clovers, and field beans.
Model organismA. pisum is the primary aphid used in laboratory studies because of its relatively large size and simplicity of rearing.
GenomeA. pisum has a haploid genome size of approximately 300Mb on four holocentric chromosomes.
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Most aphids have two genetically distinct types of life cycle within the one species: holocyclic and anholocyclic. In the holocyclic life cycle, multiple generations reproduce asexually from spring through to summer and to early autumn and then, in response to decreasing photoperiod, sexual morphs (males and egg-laying females – the oviparae) are produced, which mate and lay the overwintering eggs, which are very cold hardy. Anholocyclic clones arise from a genetically stable mutation that renders the aphids unresponsive to the decreasing photoperiodic cue that triggers the sexual morphs and egg production in the autumn. These clones reproduce asexually the whole year round, with increases and decreases in the rates of development and reproduction governed by seasonal changes in temperature. However, in contrast to their eggs, the overwintering ‘active stages’ of anholocyclic clones are much less cold hardy – mortality increases from 0% to >90% as the temperature decreases from around –5°C to <–15°C.
The holocyclic life cycle of the pea aphid begins at spring and continues up to the moment when the insects start laying eggs for overwintering. In warm climates adult insects can continue feeding and parthenogenetic reproduction even in winter months.
Lacking larval and pupal stages aphid's metamorphosis is incomplete.
- Egg In fall oviparous (sexual) females lay fertilized eggs that hatch the follwing spring; the total period of egg development is approximately 100 days; this period is considered as an embryonic diapause, a physiological phenomenon of slow development under certain conditions; all insects that hatched from the eggs are females which reproduce by viviparous parthenogenesis.
- Nymph Each asexual adult female gives birth up to 4-12 female nymphs per day; nymph develops into mature female for 7-10 days; when the colony becomes overcrowded some winged females are produced; the winged insects migrate to infest other plants.
- Adult There are following types of adults: asexual (viviparous parthenogenetic) females, which can be wingless or winged; sexual (oviparous) females, and males, which appear when temperatures become colder and light period shorter; life span of an adult is about 30 days.
Aphids preferentially inhabit temperate regions of northern hemisphere. They are particularly well adapted to regions with cold winter because their eggs are very cold hardy. The rate of development in aphids is directly dependent on temperature. The minimum tempereature at which development of A. pisum can proceed ranges between 2.3 and 6.3 °C. A female aphid requires a certain number of degree-days above the threshold to reach adulthood (99-147 in A. pisum). This is a particularly short generation time even among insects. In some european countries aphids are mostly living in suboptimal temperature conditions. Therefore, global warming would favor the proliferation of aphids. For example, an increase in temperature of only 2°C would allow the number of generations produced per year to increase from 18 to 23 in the UK.
Other biological functions influenced by temperature include dispersal and reproduction. Higher temperatures increase both the number of winged individuals produced and their flying capacity. Lower temperature thresholds for flight are generally around 13-16°C and upper thresholds around 31°C.
Sustained temperatures above 20°C might delay or even totally prevent sexual reproduction in aphids thus allowing parthenogenetic reproduction and the survival of active individuals throughout the year.
Aphids are also affected by environment through the host plants. Increases in CO2 and O3 that affect plants negatively elicit varied responses depending on aphid species and it is not possible to establish general rules for all aphid populations.
At a pan-European scale, the EXAMINE observation network has provided evidence for an increase in the number of aphid species present over the last 30 years and for earlier spring flights.Back to top
Ogawa K., Miura T. Two developmental switch points for the wing polymorphisms in the pea aphid Acyrthosiphon pisum. Evodevo. 2013 Nov 1;4(1):30
This species reproduces by thelytokous parthenogenesis in spring and summer under long day length and high temperatures. Males and oviparous females only appear in late autumn and produce fertilized eggs for overwintering. Viviparous females exhibit wing polyphenism, and males exhibit genetic wing polymorphism. Fundatrices and oviparous females are monomorphic and wingless. WD: winged, WL: wingless.
Ogawa K., Miura T. Aphid polyphenisms: trans-generational developmental regulation through viviparity. Front Physiol. 2014 Jan 24;5:1.
(A) Schematic diagram of a typical holocyclic life cycle of aphids, (B) sexual individuals (male and oviparous female) of Acyrthosiphon pisum, (C) viviparous female of A. pisum. Aphids reproduce by thelytokous parthenogenesis in spring and summer under conditions of long day length and high temperatures. In aphids with a holocyclic life cycle, males and oviparous (sexual) females appear in late autumn and produce fertilized eggs for overwintering. Aphids employ the XO sex-determination system. Therefore, viviparous and oviparous females possess two X chromosomes, while males possess only one X chromosome. Males are produced parthenogenetically with the random loss of one X chromosome during the maturation division. Although oviparous females and males produce haploid oocytes and sperm, respectively, by reductive meiosis, only sperm possessing an X chromosome are viable (sperm lacking an X chromosome are degenerate). Therefore, the next generation, which will hatch as fundatrices in the spring, is entirely female (XX). Viviparous, viviparous parthenogenetic female; Oviparous, oviparous sexual female.
Chittka L, Döring TF. Are autumn foliage colors red signals to aphids? PLoS Biol. 2007 Aug;5(8):e187. (PMID: 17696643)
At the beginning at this decade our view that the beauty of autumn leaves is only a by-product of physiological processes inside the doomed leaves were challenged. According to the new hypothesis, trees with particularly strong coloration send an honest signal to aphids, informing them of the strength of anti-herbivore defenses of these trees. But to appropriately predict the responses of aphids to colors requires us not only to examine the physiology of their eyes (inset lower right: scanning electron micrograph of the eye of the black bean aphid Aphis fabae, courtesy of J. Hardie) but also their behavioral responses to colors under controlled laboratory conditions (inset, upper left: the foxglove aphid Aulacorthum solani probing a yellow artificial target; photo by S. Kirchner).
- Le Trionnaire G et al. Shifting from clonal to sexual reproduction in aphids: physiological and developmental aspects. Biol Cell. 2008 Aug;100(8):441-51.
- Bale JS, Hayward SA. Aphids in the face of global changes. C R Biol. 2010 Jun-Jul;333(6-7):497-503.
- Le Ralec A, Anselme C, Outreman Y, Poirié M, van Baaren J, Le Lann C, van Alphen JJ. Evolutionary ecology of the interactions between aphids and their parasitoids. C R Biol. 2010 Jun-Jul;333(6-7):554-65.
- Funkhouser LJ, Bordenstein SR. Mom knows best: the universality of maternal microbial transmission. PLoS Biol. 2013;11(8):e1001631.
- PubMed: free full text articles about aphids