Aphid
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There are 10 families: |
Aphids or greenfly, plant lice (superfamily Aphidoidea) are small plant-feeding insects (1 to 10 mm). Of all 4,000 species of known aphids (distributed in 10 families), around 250 are serious pests for agriculture and forestry as well as an annoyance for gardeners. Important natural predators include ladybirds, hoverfly larvae and lacewings.
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Anatomy
The most typical organ of aphids is their piercing-sucking mouthparts called stylets. They have soft bodies, long thin legs and might or might not have wings. If wings are present, they are lacy, transparent and only have 1 prominent longitudinal vein. Aphids also have a proboscis originating between and behind the forelegs. Aphids' antennae are composed of 2 thick basal segments and a flagellum with upto 4 segments. The last of these 4 segments is divided into a proximal part and a thinner distal part (called process terminalis).
Aphids have two compound eyes and two ocular tubercles made up of 3 lenses, each of which is located behind and above the compound eyes. They have 2 tarsal segments. Besides, The 5th abdominal segment bears a pair of tubes on the dorsal surface named siphunculi (cornicles), which are upright and point backwardly. A cauda is usually present below and between them on the last abdominal segment.
Aphid.jpg
Diet
Similar to related superfamilies they passively feed on sap of phloem vessels in plants. This sap being kept under high pressure, once a phloem vessel is punctured, it is forced into the food canal. Aphids actively 'drink' (suck) from xylem vessels when thirsty.
Some species of ants "farm" aphids, supplying them with leaves to eat, and eating the honeydew that the aphids secrete. Many aphids are host to an endosymbiont bacteria, Buchnera, which synthesizes the essential amino acids that are absent in the phloem that the aphids eat.
Ant_cultivating_aphids.jpg
Ant cultivating aphids
Reproduction
For part of all of their life, aphids are often found to be parthenogenetic. At different times of the year, they can be viviparous or oviparous. During spring and summer, aphids are often parthenogenetic and viviparous and then give birth sexually during autumn. Therefore aphids are said to undergo cyclical parthenogenesis or to have a holocyclical life circle.
With that said, male and female aphids mate in autumn. Sexual females, but also asexual ones, have 2 sex chromosomes while sexual males only have 1.
Distribution
Aphids are world-wide, but they are most common in temperate zones.
Food source
Most aphids are monophaguous (i.e. feeding only on 1 species of plant).
Evolution
Aphids probably first appeared 280 millions of years ago, in the Carboniferous. They probably fed on non-flowering plants like Cordaitales or Cycadophyta. The oldest known aphid fossil is one of the species Triassoaphis cubitus from the Triassic. There were relatively few species of aphids at that time, and the number of species only considerably increased since the appearance of angiosperms 160 millions of years ago. This is due to the fact that angiosperms provide an occasion for aphids to get specialized.
Aphids have not always looked like they do nowadays. Organs like the cauda or the siphunculi did not evolve until the Cretaceous.
Aphids_on_broccoli.jpg
External links
- Aphid.info - more about aphids (http://www.aphid.info)
- More photos of ladybugs eating aphids (http://www.pollinator.com/gallery/June/ladybug.htm)ar:من