Aphids: Tiny insects with giant impact

What are aphids?

Aphids are small (2–4 mm long) pear-shaped insects, notable for their soft bodies, long legs, and antennae. They display a remarkable variety of colors, ranging from white and gray to vibrant yellow and pink, and some feature a protective waxy or woolly coating, as seen in “woolly aphids”. Most aphids are easily recognized by their two protruding tubes at their back end, called siphunculi or cornicles, which presumably release chemical compounds that deter natural enemies. 

Another feature relevant for aphid characterization and ecological interactions is their syringe-like stylet (mouthparts), which allows aphids to pierce plant tissues and feed on sugary sap. As they feed, aphids release honeydew. This sugary excretion supports pathogenic fungal growth and serves as a food source for other insects, such as ants that keep aphids as livestock. (Read more about this in our article “Two-faced ants”.)

Just like a Matryoshka doll 

Imagine a Matryoshka doll, consisting of a set of nested dolls where each one opens to reveal a smaller one inside. Did you know that aphid asexual reproduction can be just like that? This phenomenon, called by scientists "telescoping of generations", occurs because aphids in the asexual phase give birth to live nymphs instead of eggs, and, for that, these females must carry developing embryos within their bodies. Astonishingly, these developing embryos already contain embryos within themselves, reminiscent of a Matryoshka doll! In other words, aphids can be born pregnant, and an adult aphid can simultaneously carry embryos of both its daughters and granddaughters. 

Sweet but feared

The aphids’ appetite for plant sap is feared. Although a single aphid’s feeding typically results in minor plant damage, large populations can severely drain a plant’s energy resources, reduce growth, or even cause death. Moreover, excessive honeydew secretion can promote mold growth, leading to wilt and other problems. Despite these issues, the most significant threat aphids pose, particularly in agriculture, arises from their specialized feeding pattern. Like blood-feeding insects, aphids feeding on plant sap are effective vectors, transmitting over 50% of all plant viruses carried by vectors, making them major agents of disease in the plant world. Read more about the aphids’ armory in our article “The clone wars on planet plant”.

Bug Off: Dealing with aphid infestations

Early detection is critical for effectively managing aphid infestations. For minor outbreaks in gardens, aphids can be controlled by manual removal or by spraying them with a strong stream of water. Alternatives such as diluted soap sprays or neem oil effectively kill aphids on contact. Additionally, gardens can be further safeguarded by including plants that attract natural enemies of aphids (clover, mint, and dill), or those that typically repel aphids (catnip and garlic). 

Beneficial insects are a viable option for mitigating aphids in both gardens and agricultural crops. Currently, there are many insects commercially available that can naturally reduce aphid populations, including ladybugs, lacewings, and parasitic wasps.

Finally, chemical control is very effective for more persistent infestations. Alternative options include systemic insecticides that are absorbed by the plant and affect pests that feed on its sap, making them less harmful for other species.

*Glossary

Polyphenism: a phenomenon where clonal individuals (same genotype) display different characteristics (different phenotypes) due to environmental conditions, such as food availability, competition from overpopulation, abiotic factors, etc.