Picture of Toso Bozic

Toso Bozic

Tree/Forestry Expert

Aphids are among the most frequently and widely encountered insects on trees, shrubs, and ornamental garden plants. These small, sap-sucking insects with very high numbers for extended period of time can cause e damage to a wide range of trees, impacting their health(dieback) growth(wilting), and overall productivity. Aphids are prey for numerous beneficial insects, such as lady beetles, lacewings, and parasitic wasps. These natural enemies help regulate aphid populations.

Aphids belong to the superfamily Aphidoidea, encompassing thousands of species. These tiny insects with oval body, typically measuring 1-10 mm in length, exhibit a range of colors, including green, black, brown, yellow with few species with bright red colour. Some aphids conceal their bodies by coating themselves with waxy threads, earning them the name “woolly aphids.”

Aphids reproduce both sexually and asexually. Vast majority of all aphids, regardless of their form, are females. Males, when they do occur, are usually in present only in late summer/early autumn, during the last outdoor generation. During favorable conditions, particularly in spring and summer, aphids reproduce parthenogenetically, where females give birth to live young without mating. This allows for rapid population growth. In autumn, as conditions deteriorate, many aphid species switch to sexual reproduction, producing eggs that can overwinter and hatch in spring.

Aphids exhibit varying degrees of host specificity. Some are generalists, feeding on a wide range of plants, while others are specialists, targeting specific tree species. They are inefficient feeders, and some aphids will produce excessive amounts of a sticky substance called honeydew. Ants farm aphids for their honeydew, offering protection from predators in return. This mutualism can complicate aphid management, as ants can aggressively defend their aphid partners.

Honeydew which can be quite annoying when it accumulates on sidewalks, cars, and other surfaces. Honeydew attracts insects like ants, bees, flies, and wasps, whose presence may be the first indication of an aphid infestation.

Picture 1. Aphids protected by ants ( L ), woolly aphids on elm leaf ( C ), aphids on spruce with ants ( R )  

Aphids primarily feed on plant sap and inflict by piercing tender plant tissues and extracting large quantities of sap by using their specialized mouthparts. They can be found feeding on various parts of the host plant, including foliage, buds, flowers, fruit, twigs, and roots, often in groups. Their feeding can result in galls, curled leaves, swollen branches, and discolored or wilted leaves. Typically, aphids do not cause lasting damage to forest, shade, or ornamental trees. Aphids feeding behavior can lead to several detrimental effects on trees:

  • Nutrient depletion: Aphids deprive trees of essential nutrients by sucking sap, leading to weakened and stunted growth.
  • Leaf curling and distortion: The toxic saliva of aphids can cause leaves to curl and distort, reducing the tree’s photosynthetic ability
  • Sooty mold growth: Aphids excrete honeydew, a sticky, sugary substance that serves as a substrate for sooty mold fungi. This mold can cover leaves and branches, further hindering photosynthesis and aesthetic appeal
  • Transmission of plant viruses: Aphids are vectors for various plant viruses, worsening the damage and making trees more susceptible to disease.
  • Secondary infections: The wounds created by aphid feeding can serve as entry points for other pathogens, leading to secondary infections.

Effective aphid management on trees involves an integrated approach, combining cultural, biological, and chemical control methods:

  • Regular inspections helped detect aphid outbreaks early. Keep trees healthy.
  • Cold and heavy rainy weather conditions are key factors to reduce aphids’ populations
  • Natural enemies such beneficial insects, lady beetles,  lacewings and birds significantly affect populations
  • Using high pressure water to simple washed them off
  • Using variety of insecticides, soaps, and dormant oils to control population. These products can be effective against aphids by suffocating them or disrupting their cell membranes. They are often safer for beneficial insects compared to synthetic insecticides.
  • Products such as imidacloprid or pyrethroids can target aphids while being less harmful to beneficial insects. However, prior their use check out for beneficial insect populations
  • As aphids reproduce quickly and rapidly, whatever control you may consider repeating after week might be crucial to control high aphids’ population.

Related Posts