T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Aphids (Family: Aphididae)

Kingdom:   Animalia
Phylum:     Arthropoda
Class:        Insecta
Order:       Hemiptera
Suborder:   Sternorrhyncha
Superfamily:       Aphidoidea
Family:      Aphididae
Common name: Aphids, Plant lice

Aphids originated in the late Cretaceous about 100 million years ago, but the Aphidinae which comprises about half of the 4700 described species and genera of aphids alive today come from their most recent radiation which occurred in the late Tertiary less than 10 million years ago.
There are several thousand species in the family Aphididae, many of which are well known for being serious plant pests. They are also the family of insects containing most plant virus vectors (around 200 known) with the green peach aphid (Myzus persicae) being one of the most prevalent and indiscriminate carriers.

Aphids originated in the late Cretaceous about 100 million years ago, but the Aphidinae which comprises about half of the 4700 described species and genera of aphids alive today come from their most recent radiation which occurred in the late Tertiary less than 10 million years ago. Aphids originated in the late Cretaceous about 100 million years ago, but the Aphidinae which comprises about half of the 4700 described species and genera of aphids alive today come from their most recent radiation which occurred in the late Tertiary less than 10 million years ago.
Members of the Aphididae are soft-bodied, pear-shaped insects called aphids, as are other members of the super-family Aphidoidea. Most of them have a pair of little tubes, called cornicles, projecting from the posterior of the abdomen. Wings are not always present; winged morphs are called "alates", while wingless morphs are known as "apterous". The forewings of Aphididae alates are dotted with 4 to 6 veins below the darkened spiracles. They all have very small eyes, sucking mouthparts and fairly long antennae.
These insects are very small (a few millimeters in length), so small that they can be transported by wind through fairly long distances. They are often green, but might be red or brown as well. They move quite slowly and cannot jump or hop. Aphids excrete a sugary liquid called honeydew, because the plant sap from which they feed contains excess carbohydrates relative to its low protein content. To satisfy their protein needs, they absorb large amounts of sap and excrete the excess carbohydrates. Honeydew is used as food by ants, honeybees and many other insects. A common misconception is that honeydew is secreted through the cornicles (or siphuncules which are a pair of small upright backward-pointing tubes (pores on the aphid below) found on the dorsal side of the last segment of the bodies of aphids).

The two black dots on each side of the rear of the body are the cornicle pores. These abdominal tubes exude droplets of a quick-hardening defensive fluid containing triacylglycerols called cornicle wax. There is some confusion in the literature about the function of the cornicle wax secretions.

The life cycle of aphids



When host plant quality becomes poor or conditions become crowded, some aphid species produce winged offspring, "alates", that can disperse to other food sources. The mouthparts or eyes are smaller or missing in some species and forms.
A winged female.


Photo of nymph aphids surrounding the mother aphid. They were produced parthenogenetically and viviparously.


Aphids can develop down different pathways (phenotypic plasticity). 
The production of winged or unwinged morphs in aphids is an example of two alternative developmental pathways. The winged form are assumed beneficial for locating new habitats and host plants. In the two photos below an alate aphid (winged morph) can be seen.
   





A  2mm long aphid iinside a cowl of Arisarum vulgare.
  

An aphid on watercress.Species unknown