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Ericaphis scammelli = Ericaphis fimbriata ssp. pernettyae
Blueberry aphidOn this page: Identification & Distribution Biology & Ecology Population dynamics Natural enemies Other aphids on the same host Damage & Control
Identification & Distribution:
Adult apterae of Ericaphis scammelli are usually pale yellow-green (see first picture below), but we have also found a pink form (see colour forms below). The median frontal tubercle is prominent and the antennal tubercles tend to be rather low, so that the front of the head has a W-shaped outline in dorsal view (see micrographs below). The siphunculi are long and straight, 1.4-2.0 times as long as the finger-shaped cauda, with the aperture not turned outwards, and a moderate flange (see pictures below of live and preserved Ericaphis scammelli). The body length of adult apterae is 1.5-2.4 mm.
Alate Ericaphis scammelli are usually green (see second picture above), or occasionally pink, with dark brown dorsal abdominal markings fused into a central patch, and a pale window between the siphunculi.
Image copyright Andrew Barclay, all rights reserved.
Both images above copyright Andrew Barclay, all rights reserved.
Ericaphis scammelli feed on blueberry (Vaccinium), aggregating on the stem of the growing point, and along the veins on the undersides of the leaves. The species is native to North America, but has been introduced to England, Sweden, Netherlands and Italy. In Britain it has been found on blueberry seedlings and imported plants since the 1970's, with several records in Kent in recent years. Our samples came from cultivated blueberries (Vaccinium corymbosum) in Peterborough, Cambridgeshire, and from Berry Gardens in Clock House Farm, Coxheath, Kent.
Biology & Ecology:
The identity of this species in the literature is, shall we say, rather 'fluid'. Roger Blackman in Aphids on World's Plants has synonomized Ericaphis fimbriata ssp. pernettyae with Ericaphis scammelli, where Ericaphis scammelli (Mason) applies to blueberry-feeding populations. He also notes that in British Columbia aphids identified as Ericaphis fimbriata are apparently monoecious holocyclic on both rosaceous and ericaceous hosts (C.-k. Chan, pers. comm.), indicating that the name is probably being applied to a complex of morphologically similar species on cultivated strawberries (Fragaria species), blueberries (Vaccinium species) and Nootka rose (Rosa nutkana).
Andrew Jensen, in Aphidtrek, feels there is insufficient evidence for a synonymy and instead refers to specimens of this species as Ericaphis fimbriata/scammelli. He also points out that there may be a problem with a photo of Ericaphis scammelli in plate 22f in Aphids on World's Plants in that it shows dark (dusky?) coloured legs and siphunculi, whereas all of Jensen's specimens (and those found by Andrew Barclay in Cambridgeshire) have pale siphunculi and legs. (Please note also that Fig. 294 in Blackman, 2010, is labelled in error as Ericaphis scammelli; it is in fact a repeat of Figure 295, Ericaphis wakibae.)
Ericaphis scammelli is usually described as being pale yellow-green, and most of those we have seen have been this colour. However, in June 2021 we visited a trial area in Kent for different blueberry varieties. A small percentage (1- 5%) of the Ericaphis scammelli were pink-orange rather than the usual green (see picture below of a second or third instar nymph).
The pictures below show two fourth instar immature alatae of Ericaphis scammelli, the first the typical green form and the second the aberrant pink-orange form.
A mature alate of the pink-orange form is shown below.
Red-green polymorphisms are not uncommon in aphids, and have been intensively studied especially in the pea aphid (Acyrthosiphon pisum) (see what about red-green polymorphisms?). Sometimes one or other morph has a cryptic value at a particular time of year. Other times the polymorphism may reflect various physiological characteristics including susceptibility to insecticides. Alternatively it could be a chance aberration that confers little or no advantage to the aphid's survival probability or reproductive performance.
Raworth & Schade (2006) determined development rate and age-specific fecundity and survival of Ericaphis fimbriata (= ? Ericaphis scammelli) virginoparae during the spring, summer and autumn on young and mature leaves of blueberry as functions of temperature. A simulation model showed that seasonal changes in development time and fecundity were capable of reducing population growth rates to near zero depending on aphid distribution with respect to young and mature leaves. The results support a combined bottom-up and top-down view of aphid population regulation and suggest that control efforts should focus on the spring, when the population growth rate is maximal.
Raworth (2004) examined the ecology and management of Ericaphis fimbriata (Hemiptera: Aphididae) in relation to the potential for spread of Blueberry scorch virus. Aphids were sampled in commercial blueberry, Vaccinium corymbosum, fields in southwestern British Columbia, Canada, from 2001 through 2003. Ericaphis fimbriata (Richards), the dominant aphid, overwintered as eggs on blueberry and emerged in late February and March during bud break. Apterous adult fundatrices were found during April. The fundatrices produced both alate and apterous virginoparae. There was a positive curvilinear relationship between production of alatae and aphid density on flower clusters, but not on leaf terminals. Peak densities in late June or early July varied from 300 to 9000 aphids per plant in different fields, suggesting that there may be considerable variation in Blueberry scorch virus transmission rates among fields infected with the virus.
Image above copyright Andrew Barclay, all rights reserved.
Production of alate virginoparae (percentage of all fourth-instar aphids with wing pads) declined from May through August. Sexual morphs were produced in late September and October. The efficacy of postbloom insecticide applications in June, by growers, was variable. Experimental trials showed that dormant oil was not effective in preventing aphid emergence. Aphids on blueberry should be controlled before bloom, before alatae are produced and large populations occur, but the efficacy of this approach in reducing virus transmission needs to be tested.
Raworth et al. (2012) looked at temporal trends in the transmission of Blueberry scorch virus in British Columbia, Canada. Every 2 weeks during the 2001-2003 growing seasons, 10-20 highbush blueberry, Vaccinium corymbosum trap plants were placed in two commercial fields in which the proportion of plants infected with Blueberry scorch virus (BIScV, all strain BC-2) ranged from 0.14 to 0.54. In 2003, Nicotiana occidentalis (Solanaceae) trap plants were placed in the same fields. After 2 weeks of field exposure, trap plants were removed and tested for BIScV for up to 5 years using serological and molecular assays. Aphids were sampled from trap plants, surrounding crop plants, and yellow-pan water traps. Nine of 938 trap plants (eight blueberry and one Nicotiana occidentalis) became infected with BIScV strain BC-2 between 13 May and 23 July. No transmission was recorded outside this time period. In three blueberry trap plants, BIScV was detected 2 years after field exposure. On crop plants, 0.4-7.0 aphids per leaf terminal were observed at peak density in June or July. In water traps, 35.6 (range 1-102) alatae were caught per month from May to July. The proportion of trap plants becoming infected during the transmission period was 0.0-0.04 depending on year and field. The data support the view that BIScV is not efficiently transmitted by aphids. The number of Nicotiana occidentalis trap plants that became infected was similar to blueberry, but aphid species infesting the two plants differed.
Image above copyright Andrew Barclay, all rights reserved.
Pansa & Tavella (2008) described aphid population dynamics on highbush blueberry in relation to the spread of Blueberry scorch virus. In 2004, infections of Blueberry scorch virus (BlScV) were detected for the first time outside North America on blueberry (Vaccinium corymbosum: Ericaceae) in Piedmont (NW Italy). In its original area, this virus is transmitted by Ericaphis scammelli in a non-persistent way. In 2005-2006, field surveys were carried out fortnightly to monitor aphid populations in a seriously infected highbush blueberry crop in the province of Cuneo. In both years, Ericaphis scammelli was the predominant aphid in the investigated highbush blueberry crop, with smaller numbers of two polyphagous species, Aphis fabae and Aphis spiraecola. Infestation levels fluctuated from 3% to 64% of buds in 2005, and from 0.3% to 35% in 2006. Using smoothed trend lines, numbers of aphids peaked in June each year. To evaluate the aphid transmission ability, during each survey from 10 to 100 specimens were transferred from infected plants to virus-free potted plants. In transmission trials. Ericaphis scammelli proved not to be a very efficient vector of the virus, with only 2/55 field-collected plants infested with aphids being positive with the ELISA test.
A 'cocktail' of aphid parasitoids (Aphiline Berry) comprising the parasitoids Aphidius colemani, Aphidius ervi, Aphidius matricariae, Aphelinus abdominalis and Praon volucre had been released at the farm. A male and female of one of the Aphidius species are shown below.
Raworth et al. (2008) surveyed the aphids, primary parasitoids and associated secondary parasitoids on blueberry in the Pacific Northwest from 1995 to 2006. Ericaphis fimbriata (= ? Ericaphis scammelli) was the principal aphid. The dominant parasitoid species were Praon unicum, a new species of Aphidius, sp. A. and Aphidius ervi. Their frequency in relation to the other primary parasitoids varied significantly with geographical area. Praon unicum dominated the frequency distribution in southwestern British Columbia, Aphidius sp. A. west of the Cascades, and Aphidius ervi east of the Cascades. Among the hyperparasitoids, pteromalids dominated, and their frequency in relation to the other secondary parasitoids was lowest in southwestern British Columbia. The parasitization rate for Praon unicum and Aphidius sp. A in southwestern British Columbia increased from May or June to a maximum in late July or early August. Praon unicum emerged in the spring 4 wk before Aphidius sp. A. The parasitization rate for Praon unicum was lower in conventional than organic fields. Whereas aphid density increased monotonically, Praon unicum had two spring peaks. A simulation model showed that these peaks could reflect discrete generations. Releases of insectary-reared Praon unicum may effectively augment the natural spring populations by creating overlapping generations.
Pike et al. (2008) described and illustrated a new parasitoid of Ericaphis scammelli, Aphidius ericaphidis. This parasitoid is widely found associated with the commercial highbush blueberries, Vaccinium corymbosum in southwestern British Columbia, Washington, and in northeastern Oregon. It is one of several species of aphidiines known to attack Ericaphis scammelli in North America. A key was provided to distinguish it from other parasitoid species of Ericaphis scammelli.
As regards predators, Andrew Barclay has observed syrphid eggs laid amongst colonies of Ericaphis scammelli on blueberries in England (see picture below).
Images above copyright Andrew Barclay, all rights reserved.
Van Herk et al. (2006) investigated whether the number of apterous Ericaphis fimbriata that fall off blueberry plants increase in the presence of coccinellid beetles, and if the apterous aphids move quickly from one plant to another in the field.. Significantly more aphids fell when one ladybird beetle was added to Ericaphis fimbriata infested blueberry branches than when zero, two, or four were added. Similar numbers of aphids fell in the presence or absence of beetles at low aphid density (10-30 aphids per terminal), but more fell in the presence of beetles at high aphid density (50-70 aphids per terminal). The time taken for aphids to move a minimum distance of 60 cm off infested plants onto uninfested plants decreased with increasing aphid density which has important implications for the spread of the virus.
Other aphids on same host:
Ericaphis scammelli has been recorded on 6 Vaccinium species (Vaccinium ashei, Vaccinium caudatifolium, Vaccinium corymbosum, Vaccinium macrocarpon, Vaccinium stenophyllum, Vaccinium vitis-idaea).
Blackman & Eastop list 8 species of aphid (including Ericaphis fimbriata & Ericaphis scammelli) as feeding on cultivated blueberries (Vaccinium corymbosum) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 7 as occurring in Britain (Show British list).
Damage and control
The damage caused by Blueberry scorch virus is shown in the pictures below.
Figure from Martin et al. (2012) under a Creative Commons Attribution 3.0 Unported License.
Blueberry scorch virus symptoms: (A) Blueberry, necrotic flowers and leaves in foreground, healthy bushes in background; (B) Blueberry showing flower necrosis and retention, silvery flowers are from previous year, brown flowers from current year; (C) Line and oakleaf patterns; (D) Chlorotic leaf margins. (E) Leaf reddening.
British Columbia Ministry of Agriculture, 2016 recommend managing the disease in blueberries as follows: (1) Purchase mother plants for propagating from reputable nurseries, and test mother plants for BIScV before propagating. (2) Carefully monitor for symptoms. (3) Test any plants showing symptoms for the virus. (4) Remove infected plants. (5) Prior to bloom, control overwintering aphids before they reproduce and disperse. After bloom, monitor plants and apply aphicide if required.
Oudemans et al. (2011) sought (a) to map the incidence of Blueberry scorch virus (BlScV) in selected fields to verify the distribution pattern, (b) to determine if BlScV was present in asymptomatic mother plants, and (c) to determine if cuttings from BlScV-infected mother plants would root, survive and transmit the virus under typical propagation conditions. Blueberry scorch virus is one of the most pervasive pathogens of highbush blueberry. The virus is aphid-vectored and exhibits a latent period between infection and symptom expression in the host plant of up to 5 years. The authors noted that in many cases they had observed BlScV symptom expression in new fields that appeared inconsistent with aphid-vectored introduction and spread. It was, therefore, speculated that the virus may be introduced through infected nursery stock. To examine this possibility, they first surveyed selected nurseries to determine if mother plants, used for propagation by cuttings, were BlScV-infected. Two nurseries were found to harbour symptomless, infected, mother plants. Cuttings from one nursery were collected from infected and non-infected plants and rooted in propagation beds. The survival and infection of cohorts from each mother plant were determined one year after planting. A significantly greater proportion of cuttings survived from non-infected mother plants (0.7) than from infected mother plants (0.5). Of the cohort from infected mother plants that survived, 40% tested positive for BlScV. They also surveyed the distribution of infected, symptomatic plants in recent 'Duke' plantings that originated from nurseries with BlScV-infected mother plants and compared distribution with older plantings with more advanced BlScV outbreaks. In all cases, the distribution of BlScV symptom development in young fields was random, which is consistent with introduction from planting stock. Older plantings showed a strong clustered distribution, which is consistent with aphid transmission. This study identified infected nursery stock as an important source of BlScV dissemination and underscored the importance of having symptomless mother plants virus-tested.