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aphid





Pea aphids extracting sap from the stem and leaves of garden peas. Image credit: Shipher Wu (photograph) and Gee-way Lin (aphid provision), National Taiwan University
Also called a greenfly, aphids are sap-feeding insects of the family Aphididae, order Homoptera. They have needle-like mouthparts with which they piece plant tissue, the pressure within this forcing the sap into the insect's gut. Because of the damage caused by their feeding and because many species carry harmful viruses, aphids are one of the world's great crop pests.

The aphid life cycle is complex, so that within a species there may be at any one time a diversity of forms: winged and wingless, reproducing sexually or by parthenogenesis.

Aphids excrete a substance known as honeydew, which is a major food source for ants and other insects.

Among the stranger biological features are that they can be born pregnant; males are sometimes lack mouths, causing them to die not long after mating; and, according to research published in August 2012, they have a rudimentary ability to capture sunlight and use it in their metabolism.


Photosynthesis in aphids

In 2010, it was discovered that aphids are capable of manufacturing carotenes in their bodies, rather than, as is the case in all other animals, obtaining these substances ready-made from their food.[1} Aphids contain large amounts of carotenes, and it is these pigments that give aphids their distinctive color. The body color can change depending on environmental conditions; for example, in a particular species, cold may favor green aphids, while warmer condition encourage a change to orange and over-population and limited resources a tendency to be white.

In plants, carotenes function as photosynthetic pigments so it was natural to ask if the high levels of self-generated carotenes in aphids might also be involved in light harvesting. Sure enough, researchers found that aphids containing the highest concentration of carotenes (the green ones) also had the highest levels of ATP – the the chemical currency of energy transfer in all living things. Moreover, ATP production rose when the orange insects, contain an intermediate level of carotenoids, were placed in light, and fell when they were moved into darkness.[2] The indication is that aphids have a primitive ability to carry out photosynthesis. More work is now needed to verify this and to answer the question as to why they have this ability.


References

  1. Moran, N. A. and Jarvik, T. Science, 328, 624627 (2010)
  2. Valmalette, J. C. et al. Sci. Rep. http://dx.doi.org/10.1038/srep00579 (2012).

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   • ZOOLOGY