Giant oak aphid

Systematic position: The giant oak aphid (Lachnus roboris) is a member of the order Hemiptera and the family Aphididae. It is recognized as one of the largest aphid species found in temperate forest ecosystems across Europe and parts of Asia.

Host plants: The primary hosts for this species are trees belonging to the genus Quercus (oaks). It is commonly found on both pedunculate and sessile oaks. In some cases, it can also infest sweet chestnut (Castanea sativa), though it is most frequently associated with oak-dominated habitats.

Biology and life cycle: Lachnus roboris is a monoecious species, meaning it completes its entire life cycle on a single host plant species. It overwinters as eggs deposited on the bark of twigs. In the spring, stem mothers hatch and begin reproducing parthenogenetically. Several generations of wingless and winged females follow throughout the summer, with sexual reproduction occurring in the autumn before egg-laying.

Damage and economic impact: Large colonies aggregate on the bark of shoots and young branches. By feeding on phloem sap, the aphids extract significant amounts of nutrients, leading to reduced vitality and stunted growth in young trees. The secretion of honeydew promotes the growth of sooty mold, which creates a dark crust on the bark and interferes with the physiological processes of the tree.

Control measures: In nursery settings, control is typically achieved through the application of systemic insecticides during the peak periods of infestation. In natural forest environments, intervention is rarely necessary, as natural predators are highly effective. Key biological control agents include:

• Ladybirds (Coccinellidae)
• Green lacewings (Chrysopidae)
• Hoverfly larvae (Syrphidae)
• Parasitoid wasps