Synonyms and other taxonomic changes
Taxonomy on BG follows(1)
Aphids are generally small insects ranging from ~1-6mm in body length.
Most aphids can be identified to family level by two tubelike projections on the posterior, called cornicles or siphunculi
, although in some exceptions the siphunculi are greatly reduced or absent. The siphunculi emit pheromones to alert other aphids in the colony when danger is nearby. They also offer mechanical protection, as the fluid emitted can gum up the mouthparts of predators.
Species identification often requires specific views of the specimen, and many cannot be reliably identified with images. Aphids are often difficult to identify with a well placed slide mounted specimen and a high powered scope due to their small size and often minor differences in characters used for identification. For example, two species may be separated by the shape and number of secondary sensoria on antennal segment three, which is not very easy to see in photographs.
When submitting images of aphids, more angles and views increase the likelihood of identification. Taking pictures of different morphs is also really helpful. Alate forms can be easier to ID than apterous, and some forms such as oviparae are poorly known so they often can't be identified beyond family. Immature aphids generally cannot be reliably identified beyond family either because the characters used for identification are not fully developed.
Species identification is usually easier if host plant is known, but similar aphid species may colonize the same host. An attempt to organize aphid images by host plant
Aphids on the World's Plants
- Worldwide fauna with keys specific to host plants.
- European and globally distributed species.
Widespread. Aphids are unusual compared to other insects, because their diversity is higher in temperate regions and lower in the tropics.
Colonizing various plants. Feeding preference can affect what part of a plant the aphid is on, such as the stem or the back of leaves.
Different species have what are called peak flights during the growing season. Males are usually observed in the fall, and different morphs can also be present at specific times.
Aphids are phloem feeders, they use their sucking piercing mouthparts to suck juices from plants. Some are restricted to a single plant species or group of related plants. Others may alternate between two entirely unrelated host plants as a necessary part of their life cycle (e.g. Dysaphis plantaginea
begins the year on apple, then migrates to narrow-leaved plantain for several generations before winged adults return to apple trees where they produce eggs that will overwinter). Aphids that do alternate host plants are called heteroecious, and those that do not host alternate are known as monoecious. Aphids that feed on multiple species of plant are known as polyphagous, a few plants (usually related) is oligophagous, and if they only utilize one species of plant they are monophagous.
Aphids can follow two types of life cycle, holocyclic and anholocyclic. Holocyclic species alternate between sexual and asexual (parthenogenetic
) reproduction. Over-wintering eggs produced by sexual reproduction hatch in the spring. The aphids that hatch from those eggs are wingless parthenogenetic females known as fundatrices. The fundatrices give live birth to more females. The second generation of asexual females are known as viviparae, because they hold embryos in their bodies to give birth to live young. As the colony grows winged viviparous females known as alatae may be produced, although they are unknown in some species. In autumn as the photoperiod shortens and temperature decreases, male forms and egg-laying females called oviparae are produced. After mating, the oviparae lay fertilized eggs which overwinter until the spring. In anholocyclic species there is no sexual reproduction, only parthenogenetic reproduction. This is especially common in warm climates where overwintering is unnecessary. There are some anholocyclic species, such as Aphis nerii
, where males have never been observed in the wild.
Feeding aphids excrete a sugar-rich liquid known as honeydew, often consumed by ants who tend aphid colonies and protect them from predators in exchange. Ants may be herding aphids and "milk" them by stroking the aphids with their antennae, hence the common name Ant Cows. Some ant species move aphids from one plant to another when the food supply is insufficient, or even take aphid eggs into their nests to help them overwinter.
Predators of aphids include (left to right, below) lacewing larvae, ladybird beetles and larvae, harvester butterfly caterpillars, and syrphid fly larvae.
Aphids are also attacked by parasitic wasps, which lay eggs inside them. Parasitized aphids swell, change color, and are eventually killed by the developing wasp inside. These are referred to as "aphid mummies."
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