Eyes open for Aphids!
Aphids are small sap-sucking insects. Common names include greenfly and blackfly, although individuals within a species can vary widely in colour and size. There have been no less than 4.000 different types of them described worldwide, among them a good 250 that are considered to be pests of crops and ornamentals. But outside of that, Aphids play a significant role in the entire environmental system.
The life cycle of the Aphid can progress with having sex and without sex… it is - let’s say - it is complicated.
Wingless females, called stem mothers, reproduce without fertilization, by the so called parthenogenesis, from early spring throughout the summer. These stem mothers are unique in that way they produce living young Aphids (this is called viviparity) as opposed to laying eggs, which occurs in most other insects. The flightless females giving birth to live female nymphs—who may also be already pregnant, an adaptation scientists call ‘telescoping generations’. Still without the involvement of males!
Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Eventually the plant containing the stem mother and her offspring becomes overcrowded. About the time when they are ready to move house, some offspring develop into adults with two pairs of large membranous wings. These winged adults fly to new grazing grounds or to the next plant to colonize. (This circle can just go on like that, the unfinished or Hemimetabolism Circle)
In late summer both males and females are produced. The first generation is still been reproduced with the trick of the parthenogenesis, but after that it is a sexual reproduction. In cooler climates this Generation would develop wings to fly to more protected spots and hide their eggs well, so it will survive the winter’s frosty conditions. So, after they mate, the female lays eggs that survive the winter. (This is called a full or Holometabolous circle)
Although Aphids seem rather harmless (and yes there’s usually a predator hungrily on the lure for them) Aphids are among the most destructive insect pests on cultivated plants in temperate regions. They weaken the plant by sucking sap and that might lead to deformation on new growths as well as on flowers, which might still be acceptable, but wait! There’s more to that! Aphids act as vectors for plant viruses!! Simply by sucking on one plant and going to the next plant to “bite” into it as a hungry Vampire. For us Orchid enthusiasts, it’s totally unacceptable.
Another issue arises, that is quite often overseen. What an organism eats will be digested, and so what goes in one end - will come out the other end. Aphids do like to suck on the Phloem, the sugar side of the plant, which lays underneath the leaves. On hot days the pressure inside the vascular system of a plant is quite high, Aphids have to regulate their own pressure, by dropping out the extra of their plant sap intake. Together with the excrement this so called honey dew is perfect for growing grey mold that not only weakens the plant, by the secondary infection, but also minimizes the clean leaf surface that’s needed for the photosynthesis.
Control of aphids is not easy. Insecticides do not always produce reliable results, given resistance to several classes of insecticides and so systemic insecticides such as GroVentive are delivering a reliable performance. On a garden scale, water jets and soap sprays (3%) could be quite effective. On a garden scale, water jets and soap sprays (3%) could be quite effective. The fact that Aphids often feed on the undersides of leaves means they are therefore invisible for insects that are on the fly through ‘take-away’ hunt for prey. For a more sustainable approach, natural enemies achieve except in enclosed environments such as greenhouses. Aphids are often controlled by natural enemies such as ladybird beetles, aphidlions (my favourite, a cool guy, check it out!), and lacewings.
Ant Mutualism
Fun Fact: In the way of a true insect conspiracy, some species of ants actually farm aphids; protecting them on the plants where they are feeding, and consuming the honeydew the aphids release. This is a mutualistic relationship, with these dairying ants milking the aphids by stroking them with their antennae. Although mutualistic, the feeding behavior of aphids is altered by ant attendance. Aphids attended by ants tend to increase the production of honeydew in smaller drops with a greater concentration of amino acids increasing the risk of plant infection.