Editing Aphid (section)

==Diet==
[[File:Woolly Aphids.jpg|thumb|Woolly Aphids on Apple tree branch]]
Many aphid species are monophagous (that is, they feed on only one plant species). Others, like the green peach aphid, feed on hundreds of plant species across many [[family (biology)|families]]. About 10% of species feed on different plants at different times of the year.<ref name="Emden">{{cite book |author1=van Emden, Helmut F. |author2=Harrington, Richard |title=Aphids as Crop Pests |url=https://books.google.com/books?id=tH46DwAAQBAJ&pg=PA189 |year=2017 |publisher=CABI |isbn=978-1-78064-709-8 |pages=189–190}}</ref>

A new host plant is chosen by a winged adult by using visual cues, followed by olfaction using the antennae; if the plant smells right, the next action is probing the surface upon landing. The stylus is inserted and saliva secreted, the sap is sampled, the xylem may be tasted and finally, the phloem is tested. Aphid saliva may inhibit phloem-sealing mechanisms and has pectinases that ease penetration.<ref>{{Cite journal |last1=Powell |first1=Glen |last2=Tosh |first2=Colin R. |last3=Hardie |first3=Jim |date=2005 |title=Host plant selection by aphids: Behavioral, Evolutionary, and Applied Perspectives |journal=Annual Review of Entomology |volume=51 |issue=1 |pages=309–330 |doi=10.1146/annurev.ento.51.110104.151107|pmid=16332214 }}</ref> Non-host plants can be rejected at any stage of the probe, but the transfer of viruses occurs early in the investigation process, at the time of the introduction of the saliva, so non-host plants can become infected.<ref name=Emden/>

Aphids usually feed passively on [[sap]] of [[phloem]] vessels in plants, as do many other hemipterans such as scale insects and cicadas. Once a phloem vessel is punctured, the sap, which is under pressure, is forced into the aphid's food canal. Occasionally, aphids also ingest [[xylem]] sap, which is a more dilute diet than phloem sap as the concentrations of sugars and amino acids are 1% of those in the phloem.<ref>{{Cite journal |author1=Spiller, N. J. |author2=Koenders, L. |author3=Tjallingii, W. F. |year=1990 |title=Xylem ingestion by aphids – a strategy for maintaining water balance |journal=Entomologia Experimentalis et Applicata |volume=55 |issue=2 |pages=101–104 |doi=10.1007/BF00352570|doi-broken-date=1 November 2024 }}</ref><ref name="Fisher">{{cite book |author=Fisher, D. B. |year=2000 |chapter=Long distance transport |pages=[https://archive.org/details/biochemistrymole00buch/page/730 730–784] |editor1=Buchanan, Bob B. |editor2=Gruissem, Wilhelm |editor3=Jones, Russell L. |title=Biochemistry and Molecular Biology of Plants |edition=4th |publisher=[[American Society of Plant Physiologists]] |location=[[Rockville, Maryland]] |isbn=978-0-943088-39-6 |chapter-url=https://archive.org/details/biochemistrymole00buch |url=https://archive.org/details/biochemistrymole00buch/page/730 }}</ref> Xylem sap is under negative hydrostatic pressure and requires active sucking, suggesting an important role in aphid physiology.<ref>{{cite journal |author1=Malone, M. |author2=Watson, R. |author3=Pritchard, J. |year=1999 |title=The spittlebug ''Philaenus spumarius'' feeds from mature xylem at the full hydraulic tension of the transpiration stream |journal=New Phytologist |volume=143 |issue=2 |pages=261–271 |doi=10.1046/j.1469-8137.1999.00448.x |jstor=2588576|doi-access=free |bibcode=1999NewPh.143..261M }}</ref> As xylem sap ingestion has been observed following a dehydration period, aphids are thought to consume xylem sap to replenish their water balance; the consumption of the dilute sap of xylem permitting aphids to rehydrate.<ref>{{cite journal |author1=Powell, Glen |author2=Hardie, Jim |year=2002 |title=Xylem ingestion by winged aphids |journal=[[Entomologia Experimentalis et Applicata]] |volume=104 |issue=1 |pages=103–108 |doi=10.1023/A:1021234412475|doi-broken-date=1 November 2024 }}</ref> However, recent data showed aphids consume more xylem sap than expected and they notably do so when they are not dehydrated and when their fecundity decreases. This suggests aphids, and potentially, all the phloem-sap feeding species of the order Hemiptera, consume xylem sap for reasons other than replenishing water balance.<ref name="Pompon">{{cite journal |author1=Pompon, Julien |author2=Quiring, Dan |author3=Giordanengo, Philippe |author4=Pelletier, Yvan |year=2010 |title=Role of xylem consumption on osmoregulation in ''Macrosiphum euphorbiae'' (Thomas) |journal=[[Journal of Insect Physiology]] |volume=56 |issue=6 |pages=610–615 |doi=10.1016/j.jinsphys.2009.12.009 |pmid=20036244 |bibcode=2010JInsP..56..610P |url=http://www.u-picardie.fr/PCP/data/pub/2010-Pompon%20et%20al.J%20Insect%20Physiol.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110716221349/http://www.u-picardie.fr/PCP/data/pub/2010-Pompon%20et%20al.J%20Insect%20Physiol.pdf |archive-date=16 July 2011 }}</ref> Although aphids passively take in phloem sap, which is under pressure, they can also draw fluid at negative or atmospheric pressure using the cibarial-pharyngeal pump mechanism present in their head.<ref>{{cite book |title=Regulatory mechanisms in insect feeding|author1=Kingsolver, J. G. |author2=Daniel, T. L. |publisher=Springer |year=1995 |editor1=Chapman, R. F. |pages=60–65 |chapter=Mechanics of Food Handling by Fluid-Feeding Insects |editor2=de Boer, Gerrit}}</ref>

Xylem sap consumption may be related to [[osmoregulation]].<ref name="Pompon" /> High osmotic pressure in the stomach, caused by high sucrose concentration, can lead to water transfer from the hemolymph to the stomach, thus resulting in hyperosmotic stress and eventually to the death of the insect. Aphids avoid this fate by osmoregulating through several processes. Sucrose concentration is directly reduced by assimilating sucrose toward metabolism and by synthesizing [[oligosaccharide]]s from several sucrose [[molecule]]s, thus reducing the solute concentration and consequently the osmotic pressure.<ref>{{cite journal |author1=Ashford, D. A. |author2=Smith, W. A. |author3=Douglas, A. E. |year=2000 |title=Living on a high sugar diet: the fate of sucrose ingested by a phloem-feeding insect, the pea aphid ''Acyrthosiphon pisum'' |journal=[[Journal of Insect Physiology]] |volume=46 |pages=335–341 |pmid=12770238 |doi=10.1016/S0022-1910(99)00186-9 |issue=3|bibcode=2000JInsP..46..335A }}</ref><ref>{{cite journal |author1=Wilkinson, T. L. |author2=Ashfors, D. A. |author3=Pritchard, J. |author4=Douglas, A. E. |year=1997 |title=Honeydew sugars and osmoregulation in the pea aphid ''Acyrthosiphon pisum'' |journal=Journal of Experimental Biology |volume=200 |issue=11 |pages=2137–2143 |doi=10.1242/jeb.200.15.2137 |pmid=9320049 |bibcode=1997JExpB.200.2137W |url=http://jeb.biologists.org/cgi/reprint/200/15/2137 |access-date=2010-10-18 |archive-date=2008-08-21 |archive-url=https://web.archive.org/web/20080821153456/http://jeb.biologists.org/cgi/reprint/200/15/2137 |url-status=live }}</ref> Oligosaccharides are then excreted through honeydew, explaining its high sugar concentrations, which can then be used by other animals such as ants. Furthermore, water is transferred from the [[hindgut]], where osmotic pressure has already been reduced, to the stomach to dilute stomach content.<ref>{{cite journal |author1=Shakesby, A. J. |author2=Wallace, I. S. |author3=Isaacs, H. V. |author4=Pritchard, J. |author5=Roberts, D. M. |author6=Douglas, A. E. |year=2009 |title=A water-specific aquaporin involved in aphid osmoregulation |journal=Insect Biochemistry and Molecular Biology |volume=39 |issue=1 |pages=1–10 |pmid=18983920 |doi=10.1016/j.ibmb.2008.08.008|bibcode=2009IBMB...39....1S }}</ref> Eventually, aphids consume xylem sap to dilute the stomach osmotic pressure.<ref name="Pompon" /> All these processes function synergetically, and enable aphids to feed on high-sucrose-concentration plant sap, as well as to adapt to varying sucrose concentrations.<ref name="Pompon"/>

Plant sap is an unbalanced diet for aphids, as it lacks [[essential amino acid]]s, which aphids, like all animals, cannot synthesise, and possesses a high [[osmotic pressure]] due to its high [[sucrose]] concentration.<ref name="Fisher"/><ref>{{cite journal |author1=Dadd, R. H. |author2=Mittler, T. E.|author2-link=Thomas E. Mittler |year=1965 |title=Studies on the artificial feeding of the aphid ''Myzus persicae'' (Sulzer) – III. Some major nutritional requirements |journal=Journal of Insect Physiology |volume=11 |issue=6 |pages=717–743 |pmid=5827534 |doi=10.1016/0022-1910(65)90154-X|bibcode=1965JInsP..11..717D }}</ref> Essential amino acids are provided to aphids by bacterial [[endosymbionts]], harboured in special cells, [[bacteriocyte]]s.<ref>{{cite book |author=Buchner, Paul |year=1965 |title=Endosymbiosis of animals with plant microorganisms |publisher=[[Interscience]] |isbn=978-0-470-11517-6}}</ref> These symbionts recycle glutamate, a metabolic waste of their host, into essential amino acids.<ref>{{cite journal |author1=Whitehead, L. F. |author2=Douglas, A. E. |year=1993 |title=A metabolic study of ''Buchnera'', the intracellular bacterial symbionts of the pea aphid ''Acyrthosiphon pisum'' |journal=Journal of General Microbiology |volume=139 |pages=821–826 |url=http://mic.sgmjournals.org/cgi/reprint/139/4/821.pdf |doi=10.1099/00221287-139-4-821 |issue=4|doi-access=free }}</ref><ref>{{cite journal |author1=Febvay, Gérard |author2=Liadouze, Isabelle |author3=Guillaud, Josette |author4=Bonnot, Guy |year=1995 |title=Analysis of energetic amino acid metabolism in ''Acyrthosiphon pisum'': a multidimensional approach to amino acid metabolism in aphids |journal=Archives of Insect Biochemistry and Physiology |volume=29 |issue=1 |pages=45–69 |doi=10.1002/arch.940290106}}</ref>