NAME OF THE ORGANISM: Dasineura tetensi (DASYTE)

Evaluation continues

Listed in Standard PM 4-9 Certification scheme for Ribes. However, in responses to the questionnaire, NL and SI supported deregulation in the EU because 'no serious impact' on fruit production. The Fruit SEWG also assessed whether plants for planting was a significant pathway. Evaluation continues on these criteria.

Candidate by default

Dasineura tetensi has a limited host range, affecting mainly Ribes nigrum (blackcurrant) (Ellis, 2001-2024; Gagné & Jaschhof, 2021; Skuhravá & Skuhravý, 2021).
It also attacks Ribes uva-crispa (gooseberry) (Barnes, 1948 - under the name Dasineura ribicola (Kieffer); Ellis, 2001-2024) but there are doubts while it is an important pest for gooseberry (Gagné & Jaschhof (2021) doesn’t list it as a host for the species).
It may also attack Ribes rubrum (redcurrant) (Piotrowski et al., 2021 & Hellqvist, 2001a) but this has yet to be confirmed that this would occur naturally. Indeed, Barnes (1948) ruled out R. rubrum as an oviposition host for D. tetensi after conducting host preference experiments. A potential association of D. tetensi with R. rubrum is also reported in Hungary (Veszelka, 1981: https://agris.fao.org/search/en/providers/123819/records/64735f732c1d629bc97dcf66). In addition, a gall midge species that is currently a nomina dubia and formerly referred to as Asphodylia ribesii (Meigen) (syn. Cecidomyia ribesii) is described in Austria as causing leaf curling in R. rubrum (Barnes, 1948). This is also a potential record of Dasineura tetensi, but this cannot be confirmed because the type-material has been lost (Gagné & Jaschhof, 2021). In addition, there are references of D. tetensi from the hosts Arctostaphylos uva-ursi, Ribes alpinum and Ribes bracteosum in continental Europe (https://dbif.brc.ac.uk/invertebratesresults.aspx?insectid=2858).
The gall midge is associated with the leaves of plants for planting. It overwinters as larvae in cocoons in the soil beneath blackcurrant bushes, predominantly within the uppermost centimeter of the soil profile (Goncharova, 1967; Cross & Crook, 1999; cited in Hellqvist, 2001b). Adults emerge in late spring. The time of emergence is reported to vary greatly from year to year, even in relation to the development of black currant (Pitcher, 1958, Cross & Crook, 1999; cited in Hellqvist, 2001b). The number of generation per year varies according to the geographical situation, weather conditions and the availability of actively growing shoots for oviposition and larval development. Three or four generations appears to be normal in Western, Central and Eastern Europe (Hellqvist, 2001b; Ellis, 2001-2024).
The Fruit SEWG considered that there was insufficient information presented to be confident on whether plants for planting is a significant pathway. However, given the limited host range, plants for planting could be a significant pathway for Ribes plants, particularly those under protection.

Yes

Dasineura tetensi is an important pest in young blackcurrant plantations as well as nurseries. Its larvae cause curling and twisting of young leaves into distinctive leaf galls, older galls become necrotic. In established crops infestation with larvae reduces bush vigour, killing the terminal shoot and causing a proliferation of side shoots from lateral buds. In mother plantations, D. tetensi attack may cause up to 60% reduction in the growth of shoots, and in the nurseries the infested plants are weakened and do not grow to a suitable size (Piotrowski et al., 2020).
The blackcurrant leaf midge has become a more frequent pest of blackcurrants since the withdrawal of the broad-spectrum insecticide (a synthetic pyrethroid) that was routinely used for blackcurrant gall mite control and provided incidental control of leaf midge. The importance of the damage varies, depending on the bush/plantation age or growth phase. Attacks are of greatest significance in nurseries where new growth is critical, in new plantations where stunting of growth delays establishment, in fruiting bushes where the number of replacement shoots developing from the base is insufficient, or on regrowth in plantations that have been cut back (Mitchell et al. 2011; Fountain et al., 2015).
Sprays of synthetic pyrethroid (SP) insecticides caused substantial reductions in catches of Dasineura tetensi in sex pheromone traps and galling injury (72% and 75% resp.). However, they did not result in increases in yield or shoot growth in established commercial blackcurrant plantations.
In cut-down, re-growing bushes, SP sprays largely prevented galling injury which caused severe stunting and multiple branching (Cross et al., 2016). Failure to control leaf midge in the first year of regrowth in the untreated plots resulted in severely stunted shoot growth and branch proliferation, which was so severe that bushes failed to recover adequately in the second year, indicating the need to use insecticides to control leaf midge in re-growing bushes and by implication, in young establishing bushes (Fountain et al., 2015).
[Remark: In responses to the questionnaire, NL and SI considered that impact was 'not serious' and 'insignificant'.]
Damage reported on other Ribes species than R. nigrum are infrequent.

Medium to Major

No

Candidate

Assessment of economic impact was provided for R. nigrum (blackcurrant): significant damage recorded on this host, requiring targeted control measures. The susceptibility of blackcurrant to D. tetensi varies with cultivar variety and hybrid cross (Barnes, 1948 & Keep,1985).
Although damage reported on other Ribes species than R. nigrum are infrequent, these other species may be source of infestation if the plants are cultivated in the field or on reused substrate.

Candidate

Certification schemes and other control measures (e.g. roguing out of infested plants). Its occurrence in many growing areas, particularly in Europe, has reduced due to the widespread use of broad-spectrum pesticides for control of gall mite. However, the progressive withdrawal of such chemicals and the increasing interest in IPM strategies mean that an increase in leaf midge levels has already begun. Work to identify suitable natural predators of the midge such as Platygaster spp. that can be used in an integrated control system is in progress (James Hutton Institute, 2024).
In absence of treatments, the Fruit SEWG highlighted that the only measure available in a nursery would be the removal of infested plants and questioned whether this measure (as regulated at present in the EU Marketing Directive) was really cost effective.

Differences in susceptibility exist between blackcurrant cultivars, and resistance in R. nigrum cultivars such as 'Ben Connan' appears to be due to larval antibiosis, rather than differences in volatile profiles. A dominant gene for resistance, Dt, was identified in R. dikuscha by Keep (1985).

Candidate by default

Insufficient data available to determine whether plants for planting is a significant pathway. There is doubt whether it is an important pest for R. uva-crispa (gooseberry).