NAME OF THE ORGANISM: Chaetosiphon fragaefolii (CHTSFR)

Evaluation continues

EPPO Standard PM 4/11 Certification scheme for strawberry recommends inspection for Chaetosiphon fragaefolii, with 0% tolerance in visual inspection for nuclear stock and propagation stock I, and 1% tolerance for propagation stock II and certified material. However, when responding to the questionnaire, DE, ES, NL and SI supported deregulation. Evaluation continues especially on the pathway. Remark: DE and NL also questioned the listing of vectors, not causing direct damage, as RNQPs.

Candidate

Chaetosiphon fragaefolii feeds on strawberry (Fragaria species) especially the cultivated varieties. In Europe it is rarely found on wild strawberry (Fragaria vesca), but in America it is found on some wild species such as the Chilean strawberry (Fragaria chiloensis). Chaetosiphon fragaefolii usually occurs on new shoots, in the crown and close to the veins on the undersides of leaflets (Dransfield & Brightwell).
The life cycle of the strawberry aphid includes overwintering eggs, nymphs and adult apterae (wingless), and alatae (winged). For most of the year there are only females, which are viviparous (live-bearing). Their offspring is produced parthenogenetic (asexual reproduction – clones of the mother). The species mainly overwinters as parthenogenetic forms, although sexual forms have been produced in the laboratory (Dransfield & Brightwell). Oviparae forms (winged reproductive females and wingless males) may occur in greenhouse and laboratory culture but have not been reported from the field (Rondon et al., 2017).
C. fragaefolii can move with propagation material; the aphid was introduced into Florida with nursery material and became established (Rondon & Cantliffe, 2004: Rondon et al., 2017).
From a genetic study, it looks that C. fragaefolii do not disperse over a large geographical distance by flight, therefore long-distance movement is likely to be via movement of host plants (Lavandero et al., 2012). The only way to find out about their potential dispersal distance in Europe would be to carry out a similar study here. Since higher average wind speeds reduce populations, these aphids are probably not great at flying.
C. fragaefolii is able to transmit at least four important viruses: strawberry crinkle virus (SCV), strawberry mottle virus (SMoV), strawberry mild yellow edge virus (SMYEV) and strawberry vein banding virus (SVBV). These viruses are transmitted in a semi-persistent or persistent way. Because these viruses each have different virus–vector interactions, it is important to know which viruses are present in the area because aphid management will be different for nonpersistent transmission compared with persistent or propagative persistent transmission (Martin & Tzanetakis, 2013).
If there is not a strawberry-free period between crops and the viruses can persevere in the production area and be spread from crop to crop through their vector, it will cause yield and quality losses in subsequent plantings. A strawberry-free period serves to greatly reduce the vector population without the need for insecticides (Tzanetakis & Martin, 2017).
[In the responses to the questionnaire, SI considered that this vector was already widespread. NL highlighted that the vector was a airborne vector of viruses.]

The Fruit SEWG concluded that since the aphid populations are mainly composed of apterous individuals, their main route of transmission is on plants for planting.

Yes

Aphids usually occur on new shoots and buds in the crown of the plant and along veins on the undersides of leaves. They generally remain motionless when a plant is being examined. Chaetosiphon spp. feed exclusively on leaves and petioles, sucking out plant juices. When present in large numbers, they weaken the plant. In the process of feeding, they excrete large quantities of honeydew, which makes the fruit and leaves sticky and also promotes the growth of a black sooty mold fungus. Honeydew and sooty mold are not very harmful to the plant but can make picking difficult and render the fruit unsalable (Maas, APS, 1998).
Of far greater importance is the role of aphids in transmitting several severely degenerative virus diseases (see Aphid-Borne Viruses). Studies have shown that unless strawberry fields are isolated from virus sources and aphids are controlled, nearly 100% virus infection can occur in as short a time as 2 weeks and generally within 2 or 3 years (Maas, APS, 1998).
If growers produce in an annual system, there may not be a need for vector control. While viruses may be present and accumulate in plants over the course of the production cycle, infection rates will be under the threshold to cause economic damage (Martin & Tzanetakis 2013; Tzanetakis & Martin, 2017).
For producers using a perennial system, where the plants are maintained for production over multiple years (usually 2–4), vector control is critical if they are known to occur in the area of production. Even if virus infections are not obvious in the first season, if they accumulate over time, yield and fruit quality can decline rapidly (Martin & Tzanetakis 2013; Tzanetakis & Martin, 2017).

The strawberry aphid C. fragaefolii is considered an important pest of strawberries in open fields worldwide, including the U.S., Canada, northern Mexico, Europe, Great Britain, South Africa, New Zealand, and Australia (Dixon et al. 1987 and Blackman & Eastop 2000 in Rondon and Cantliffe, 2004). Although the direct damage caused by feeding should not be overlooked (PlantwisePlus Knowledge Bank, 2023), their populations usually don’t reach high densities (UC, 2005; Cingolani and Greco, 2018) and its main economic impact is related to its role in virus transmission (Krczal, 1982; UC, 2005; Kirschbaum, 2022). Among the viruses transmitted by C. fragaefolii (according to EPPO Global Database; accessed October, 2024), strawberry vein banding virus (SVBV00), strawberry crinkle virus (SCRV00) and strawberry mild yellow edge virus (SMYEV0) are categorised as RNQP for Fragaria in the EU Directive 2014/98/EU.

Major

No

Candidate

Aphids are found on strawberries wherever they are grown. The purpose of aphid control, except under very unusual circumstances, is to control the spread of aphid-vectored virus diseases (Maas, 1998). The economic impact was therefore rated as 'Major' for such areas (e.g. in Spain C. fragaefolii does not act as a vector; MAPA, 2019). Evidence of economic impact for C. fragaefolii is available in the literature.

Candidate

Clean planting stock, field isolation, and aphid control can greatly retard the spread of strawberry viruses (Maas, 1998).
Cultivating plants free of aphid infestation is the first and most fundamental method of control in Florida. C. fragaefolii does not spontaneously move over long distances and infestations are often the consequence of cultivating plant material that is already infested (Rondon et al., 2017).

Candidate