Alder buckthorn aphid

Description and Pest Characteristics

Recently, this aphid is very rarely found on potato plantations in Poland. The species may be more abundant in regions where alder buckthorn (Frangula alnus) is widespread. A. frangulae is a heteroecious aphid (linked to a primary host – alder buckthorn – Frangula alnus and a secondary host – potato, weeds Lamium sp., Capsella bursa-pastoris, Veronica sp., and others). Morphologically, it is similar to A. nasturtii, so during mass surveys, the two species are often counted together. According to literature and long-term studies, A. frangulae is less abundant than A. nasturtii and occurs sporadically in Poland due to major environmental changes, the area of potato cultivation, and possibly climate. Older literature also confused this species with the cotton aphid A. gossypii.

Biology

• Eggs – small, oval, laid on the bark of alder buckthorn, the winter host of this species (overwinter in this stage).
• Larvae (harmful stage) – 1.2–2.1 mm long, oval, very delicate, wingless nymphs, yellow-green (see 1) or yellow-orange. Cauda and siphunculi dark. Forms dense colonies mainly on the underside of older lower leaves. Piercing-sucking mouthparts extract sap. Develop parthenogenetically through several generations of virgin females on potato (secondary host).
• Adult insect (harmful stage) – winged form (see 2), up to 2.1 mm long. Brown cauda, darker siphunculi, with a dark stripe and transverse bands between siphunculi. Summer generation is very active, acting as vectors of plant viruses transmitted to potato (PVY, PVM).

Life cycle

Alder buckthorn potato aphid is a heteroecious species. In its environment – on the primary host (alder buckthorn) and secondary host (potato) – its development is holocyclic (complete) with virgin females, winged individuals, and a sexual generation (laying eggs). Females lay eggs in autumn on the bark of the winter host, which overwinter. In spring, generations of virgin females develop on alder buckthorn, colonizing young shoots. Winged migrants then move to summer hosts, where several generations of wingless virgin females develop. During warm and dry conditions, new colonies quickly establish on newly colonized potato plants. In autumn, winged sexual females return to alder buckthorn; simultaneously, winged males arrive, copulation occurs, and eggs are laid.

Distribution and damage

The species occurs sporadically and in small numbers in Poland, mainly in warm, dry, and rainless years, and where the winter host (alder buckthorn) is present.

These aphids are primarily harmful as virus vectors, causing degradation of seed material and cultivated varieties. A. frangulae is an active vector of potato viruses M (PVM) and Y (PVY), currently the most economically important viruses in potatoes grown in Poland. Aphid pressure is generally low, but they remain important due to their virus transmission to potatoes. Vegetative reproduction of potatoes (via tubers) increases virus presence year after year, reducing yields. Therefore, seed material should frequently be replaced with new, certified stock depending on varietal virus susceptibility. Adults and colonies (nymphs) also directly damage potato green parts by sucking phloem sap, rarely causing leaf curling or deformation.

Economic threshold

Threshold is 20 aphids per 100 leaves. A single winged aphid on a plantation may already pose a threat by transferring transient virus Y and M between plants. Monitoring involves frequent field observations after planting and during summer growth. Mechanical collection can use a Johnson aspirator. Monitoring can also use yellow traps (for winged aphids) or counting aphids on the underside of middle-tier leaves (100-leaf method).

Control methods

The primary method is treating seed tubers with an insecticidal coating in spring during planting. Currently, only one such product is available – Prestige Forte 370 FS, with systemic active ingredients. Most common are foliar insecticide treatments. The first application should occur when aphids are detected on leaves or yellow traps. Subsequent treatments are applied every 7–14 days depending on actual infestation. Mineral oil sprays do not effectively kill aphids but can reduce numbers and inhibit virus spread, playing an important role in seed potato production.

Avoiding weed infestation is critical since weeds may harbor viruses, and some weeds are intermediate hosts of aphids, e.g., Aphis fabae and A. frangulae. Excessive nitrogen fertilization (>150 kg/ha) promotes vigorous plant growth, favoring aphid development. Essential oils from plants like rosemary, lavender, thyme, and peppermint have shown repellent or aphid-killing effects, though application techniques remain challenging.

Other methods to reduce aphid flights include covering ridges with chopped cereal straw or planting trap crops around the field (soy, sorghum, wheat, oats). Both methods reduce potential virus vectors and limit PVY infection of tubers.

Eliminating the winter host – alder buckthorn – and avoiding seed potato fields near buckthorn is also crucial. In regions without buckthorn, aphid populations are usually low.

Compiled by: dr inż. Tomasz Erlichowski