Aphids are a tiny family of insects with a body length that ranges between one millimeter and one centimeter. Despite their size, aphids are recognized widely as lethal and highly destructive pests. They feed on plants and not only do they steal vital nutrients from these plants, they also infect them with viruses. It may surprise you though that only 250 of the 4400 existent species of aphids are known to cause serious harm to farm crops.
What’s more surprising is the manner in which these insects give birth. A huge majority of aphid species are composed entirely of females. In fact, some of the species that do give rise to male offspring only do so in certain seasons of the year such as autumn and winter. The reproductive cycle of aphids is highly seasonal and happens asexually for a larger number of aphid species. Reproduction is thus facilitated by the female aphid also known as the fundatrix. An embryo in the fundatrix’s ovariole develops with hundreds of eggs already growing inside it. Eventually, a single season of breeding could give rise to literally billions of offspring given the right conditions. Another interesting fact worth noting is that the reproduction process is parthogenetic. This means that the offspring of an aphid will resemble its parent accurately except for its size.
With such a high re-population rate one would wonder what keeps these creatures alive. Aphids feed on the sap contained in a plant’s phloem. Some aphids actually only feed on one type of plant species (monophagists) while others devour a variety of them. This sap contains a range of amino acids and sugar which they need to survive. They however need to extract large quantities of sap due to the low nitrogen content that these amino acid possess. They also rely on endosymbiotic relationships with certain bacteria that help convert the amino acids into essential amino acids that are lacking in plant sap.
Aphids have an interesting relationship with other members of the insect family. They excrete a honeydew that is a fodder for ants. The ants at times milk off the honeydew that is excreted from aphids by stroking them as they suck on plant sap. The dependency of ants on aphid sap is so high that they assimilate them into their colonies. These ants usually take the aphids to their nests to protect them and feed them in return for a steady supply of honeydew. Given their high reproductive rates, aphids manage to live longer in the ant habitats. Each time an ant queen chooses to create a new colony, she takes with her some aphids that will spawn further generations of aphids from which honeydew can be milked. This kind of a symbiotic relationship is highly effective given the characteristics of aphids i.e. their asexual reproduction, high birth rates and their extensive feeding habits.
