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Datasheet

Neolecanium cornuparvum
(magnolia scale)

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Datasheet

Neolecanium cornuparvum (magnolia scale)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Neolecanium cornuparvum
  • Preferred Common Name
  • magnolia scale
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • Magnolia scale, Neolecanium cornuparvum, is a scale insect that is native to the eastern USA, where it is a widely distributed pest of wild and ornamental Magnolia in landscapes and nurseries. In gen...

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Pictures

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PictureTitleCaptionCopyright
Neolecanium cornuparvum (magnolia scale); adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
TitleInfestation
CaptionNeolecanium cornuparvum (magnolia scale); adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
Copyright©Sarah Vanek/Bugwood.org - CC BY-NC 3.0 US
Neolecanium cornuparvum (magnolia scale); adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
InfestationNeolecanium cornuparvum (magnolia scale); adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.©Sarah Vanek/Bugwood.org - CC BY-NC 3.0 US
Neolecanium cornuparvum (magnolia scale); close view of adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
TitleInfestation
CaptionNeolecanium cornuparvum (magnolia scale); close view of adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
Copyright©Sarah Vanek/Bugwood.org - CC BY-NC 3.0 US
Neolecanium cornuparvum (magnolia scale); close view of adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.
InfestationNeolecanium cornuparvum (magnolia scale); close view of adults infesting a magnolia (royal star magnolia (Magnolia stellata). Lexington, Kentucky, USA.©Sarah Vanek/Bugwood.org - CC BY-NC 3.0 US

Identity

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Preferred Scientific Name

  • Neolecanium cornuparvum (Thro, 1903)

Preferred Common Name

  • magnolia scale

Other Scientific Names

  • Lecanium (Neolecanium) cornuparvum (Thro) Pettit & McDaniel, 1920
  • Lecanium cornuparvum Thro, 1903

International Common Names

  • English: magnolia soft scale

EPPO code

  • NEOECO (Neolecanium cornuparvum)

Summary of Invasiveness

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Magnolia scale, Neolecanium cornuparvum, is a scale insect that is native to the eastern USA, where it is a widely distributed pest of wild and ornamental Magnolia in landscapes and nurseries. In general, non-native species of Magnolia tend to be more susceptible to attack than native US species. N. cornuparvum has also been reported on Wisteria in Connecticut. The genus and species were first reported from Canada from a specimen of N. cornuparvum collected in 1998 in southern Ontario, where the insect is now an established pest of Magnolia, having probably been spread via the plant trade. An infestation of scale insects believed to be N. cornuparvum was first observed in Hawaii on Sesbania tomentosa on Kauai in August 2004; it had significant adverse effects on this endangered species.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Hemiptera
  •                         Suborder: Sternorrhyncha
  •                             Unknown: Coccoidea
  •                                 Family: Coccidae
  •                                     Genus: Neolecanium
  •                                         Species: Neolecanium cornuparvum

Notes on Taxonomy and Nomenclature

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Magnolia scale (family Coccidae) was first described as Lecanium cornuparvum by Thro in 1903 from a specimen on magnolia in Trumansburg, New York, USA (Thro, 1903). Prior to 1903, it had been misidentified as Lecanium magnoliarum and discussed by some authors under that name (Herrick, 1929, 1931). It was later placed in the genus Neolecanium by Fernald (1903) and Sanders (1909).

Adult males of Neolecanium cornuparvum, Pseudophilippia quaintancii and Toumeyella parvicornis are unique in having antennae with nine segments, a complete dorsal pronotal ridge, the absence of a glandular pouch, and the presence of two lobes analogous to anal plates representing abdominal segment 9 dorsally. As the major groups of Coccidae have three to five unique character states, Ray and Williams (1983) proposed that N. cornuparvum, P. quaintancii and T. parvicornis be placed in a new major group, the Toumeyella group. A cladistic analysis of 17 taxa by Miller and Williams (1995) using 12 characters supported the monophyly of the Toumeyella group, which includes Mesolecanium nigrofasciatum, N. cornuparvum, P. quaintancii and Toumeyella spp.

Description

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The immobile adult female of N. cornuparvum is described and illustrated in Williams and Kosztarab (1972), Hamon and Williams (1984) and Kosztarab (1996), and the adult male (a small gnat-like insect) is described and illustrated in Ray and Williams (1983) and Miller and Williams (1995). The immature instars are described and a key for the separation of all developmental stages of the species is included in Ray and Williams (1983).

N. cornuparvum is one of the largest scale insects found in the USA. Adult females are elliptical and flat to convex, 4.3 mm to 12.4 mm long and 4.0 mm to 10 mm wide (Hamon and Williams, 1984). The antennae and legs are short and stout. In life, the body colour varies from pink-orange to dark brown, with a dark margin. Females are covered with a white waxy coating, which gradually disappears as they mature; very old females are brown (Williams and Kosztarab, 1972; Hamon and Williams, 1984; Herms and Nielsen, 2004). Overwintering nymphs are dark grey with a red-brown ridge along the middle of the back. In microscope slide mounts, N. cornuparvum can be distinguished from other scale insects by the dense pattern of small 8-shaped pores on the dorsal derm, and by having reduced legs and antennae (Williams and Kosztarab, 1972; Hamon and Williams, 1984).

Distribution

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N. cornuparvum is native to the eastern USA, where it is a widely distributed pest of Magnolia in landscapes and nurseries. In the early 1930s it was reported from Michigan (McDaniel, 1930) and Alabama, Connecticut, Florida, Indiana, Kentucky, Louisiana, Maryland, Mississippi, New York, Ohio, Pennsylvania, South Carolina, Virginia, West Virginia, and possibly Georgia (Herrick, 1931). Since then it has been reported from Maine (Ben-Dov, 1993), Massachusetts (Hamon and Williams, 1984), North Carolina (research cited in Williams and Kosztarab, 1972; Hamon and Williams, 1984; Ben-Dov, 1993), Georgia (Hamon and Williams, 1984), Tennessee (Lambdin and Watson, 1980; Ben-Dov, 1993), Harris County, Texas (Burke et al., 1994), and Wisconsin (Hamon and Williams, 1984). N. cornuparvum has become a pest in Illinois since the mid-1990s (Hortanswers, 2015). It has also spread to Ontario, Canada (Paiero, 2003), and to Hawaii (US Fish and Wildlife Service, 2010).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

North America

CanadaPresentPresent based on regional distribution.
-OntarioPresentIntroduced1998 Invasive Drysdale, 1998; Paiero et al., 2003
USAPresentPresent based on regional distribution.
-AlabamaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-ConnecticutPresentNativeHerrick, 1931; Schread, 1961; Hamon and Williams, 1984; Ben-Dov, 1993
-FloridaPresentNativeHerrick, 1931; Ben-Dov, 1993
-GeorgiaPresentHamon and Williams, 1984; Ben-Dov, 1993
-HawaiiLocalisedIntroduced2004 Invasive US Fish and Wildlife Service, 2010Kauai
-IllinoisPresentHortanswers, 2015
-IndianaPresentNativeHerrick, 1931; Osmun and Bram, 1964; Hamon and Williams, 1984; Ben-Dov, 1993
-KentuckyPresentNativeVanek and Potter, 2010b; Herrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-LouisianaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-MainePresentHamon and Williams, 1984; Ben-Dov, 1993
-MarylandPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-MassachusettsPresentHamon and Williams, 1984
-MichiganPresentMcDaniel, 1930
-MississippiPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-New YorkPresentNativeThro, 1903; Herrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-North CarolinaPresentWilliams and Kosztarab, 1972; Hamon and Williams, 1984; Ben-Dov, 1993
-OhioPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993; Herms and Nielsen, 2004; Shetlar and Andon, 2015
-PennsylvaniaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-South CarolinaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-TennesseePresentLambdin and Watson, 1980; Ben-Dov, 1993
-TexasPresentBurke et al., 1994
-VirginiaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-West VirginiaPresentNativeHerrick, 1931; Hamon and Williams, 1984; Ben-Dov, 1993
-WisconsinPresentNativeHamon and Williams, 1984; Ben-Dov, 1993

History of Introduction and Spread

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The genus Neolecanium and species N. cornuparvum were first officially reported from Canada based on a specimen collected in Hamilton, southern Ontario, in August 1998, where the insect is an established pest of Magnolia (Paiero et al., 2003).  According to the gardening website 'ICanGarden', the species is likely to have been in Ontario since at least the mid-1990s; by 1998 it was reported to have spread throughout much of Ontario where Magnolia trees are hardy in growing zone 5b [–15 to –10°F (–26.1 to –23.3°C)] or above (Drysdale, 1998).

An infestation of scale insects believed to be N. cornuparvum was first observed in Hawaii on Sesbania tomentosa at Polihale State Park on Kauai in August 2004 (US Fish and Wildlife Service, 2010).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Hawaii USA 2004 US Fish and Wildlife Service (2010); US Fish and Wildlife Service (2010d); US Fish and Wildlife Service (2010i) Island of Kauai
Ontario USA 1998 Yes Paiero et al. (2003)

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Principal habitat Harmful (pest or invasive)
Cultivated / agricultural land Principal habitat Natural
Urban / peri-urban areas Principal habitat Harmful (pest or invasive)
Urban / peri-urban areas Principal habitat Natural

Hosts/Species Affected

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Preferred hosts of N. cornuparvum in the USA are wild and ornamental species of Magnolia (family Magnoliaceae), including M. acuminata, M. acuminata var. cordata, M. liliiflora, M.× soulangeana and M. stellata (Herrick, 1931; Williams & Kosztarab, 1972; USDA Forest Service, 1985; Knox et al., 2012). N. cornuparvum is also a pest of Magnolia acuminata in Ontario, Canada (Beardmore et al., 2006). In general, non-native species of Magnolia in the USA are more susceptible to N. cornuparvum than native species. The native species M. acuminata and M. grandiflora can be infested but are rarely damaged, while M. virginiana, M. macrophylla and M. tripetala are rarely colonized (Herms and Nielsen, 2004), although an occurrence of N. cornuparvum on M. tripetala in Tennessee was reported by Lambdin and Watson (1980).

N. cornuparvum has also been reported attacking Wisteria (family Fabaceae) in Connecticut (Smith et al., 2015), and an infestation of scale insects believed to be N. cornuparvum was observed on the endangered Sesbania tomentosa (family Fabaceae) in Kauai, Hawaii (US Fish and Wildlife Service, 2010).

Although N. cornuparvum has been reported to feed on Daphne spp., Virginia creeper (Parthenocissus quinquefolia) and tuliptree (Liriodendron tulipifera), this was probably a misidentification; the scale species on these plants is likely to be Lecanium magnoliarum [=Parthenolecanium persicae] (Herrick, 1931).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
MagnoliaMagnoliaceaeMain
Magnolia acuminata (cucumber tree)MagnoliaceaeOther
Magnolia grandiflora (Southern magnolia)MagnoliaceaeOther
Magnolia liliiflora (Lily magnolia)MagnoliaceaeMain
Magnolia macrophylla (Bigleaf magnolia)MagnoliaceaeOther
Magnolia stellata (Star magnolia)MagnoliaceaeMain
Magnolia tripetalaMagnoliaceaeOther
Magnolia virginiana (sweet bay)MagnoliaceaeOther
Magnolia x loebneriMagnoliaceaeMain
Magnolia x soulangianaMagnoliaceaeMain
Sesbania tomentosaFabaceaeWild host
WisteriaFabaceaeOther

Growth Stages

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List of Symptoms/Signs

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SignLife StagesType
Leaves / yellowed or dead
Stems / dieback
Stems / external feeding
Stems / honeydew or sooty mould
Whole plant / external feeding
Whole plant / plant dead; dieback

Biology and Ecology

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Genetics

The chromosome number and genetic systems of 460 species of scale insects belonging to 14 families are listed in Gavrilov (2007). The list includes N. cornuparvum.

Reproductive Biology and Life Cycle

Reproduction in N. cornuparvum is sexual; it has one generation per year. The eggs are protected by the body of the adult female and newly hatched first-instar nymphs (crawlers) are produced from mid-summer to mid-autumn. In Ohio, crawlers emerge from the beginning of August until well into October (Herms and Nielson, 2004). The average date of egg hatch of magnolia scale in Wooster, Ohio, is 4 August, with a cumulative number of degree-days of 1938 using a base temperature of 50 °F (10 °C) and a starting date of 1 January (Herms, 2004). Unlike the adult females, the crawlers are mobile, and soon after emergence they search for a suitable site to feed, often remaining near to their mother and commonly settling in protected areas such as bark crevices or under the hollow exoskeletons of dead scales. Once they start feeding they become immobile. The first-instar nymphs overwinter, often in large aggregations, on the undersides of 1–2-year-old branches or new-growth twigs of the host plant. Overwintering nymphs are dark grey with a red-brown ridge along the middle of the back. The nymphs start feeding as the temperature rises in the spring and grow rapidly during leaf emergence when large quantities of energy-rich sap are available. There are three immature instars (first to third instar nymphs) in the female and four in the male (first and second instar nymphs, pre-pupa and pupa) (Ray and Williams, 1983). In New York, the nymphs moult around mid-May and again in the first half of June (Herrick, 1931). Adult females appear from late July through to October. Males mature earlier than females and emerge as small, pink to yellow gnat-like insects in the late spring. They do not feed; they fly in search of young adult females with which to mate, and die soon after mating. Adult females die after reproducing in the autumn and leave behind their hollow, brown exoskeletons, which may remain on the plant for many months. The scale leaves an elliptical scar when removed from the plant (Schread, 1961; Williams and Kosztarab, 1972; Hoover, 2002; Herms and Nielsen, 2004; Townsend, 2005; Gordh and Headrick, 2011; Shetlar and Andon, 2015).

Nutrition

The nymphs and adult females feed on the phloem sap of host plants, usually Magnolia spp.. The last two immature male stages, and adult males, do not feed (Shetlar and Andon, 2015).

Associations

Ants commonly attend scale insects, using the honeydew they produce as a source of sugar and nutrients. Attendant ants will defend the scale from natural enemies, and provide sanitation by removing honeydew and dead scales. Field observations by Vanek and Potter (2010a) in Kentucky showed that the ant Tetramorium caespitum constructed shelters over nymphs and adults of N. cornuparvum, and that these shelters protected the scale insects from attacks by the syrphid predator Ocyptamus costatus. Vanek and Potter (2010b) carried out field studies in which ants were excluded from Magnolia stellata plants infested with N. cornuparvum and calico scale (Eulecanium cerasorum). Ten ant species were found tending N. cornuparvum in control treatments, and ant exclusion led to an 82% reduction in the number of N. cornuparvum reaching the adult stage after one year.

Climate

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ClimateStatusDescriptionRemark
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Hyperaspis signata Predator All Stages not specific
Ocyptamus costatus Predator All Stages not specific

Notes on Natural Enemies

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Few natural enemies have been reported specifically for N. cornuparvum. Natural enemies of soft scale insects in general include predatory beetles (e.g. families Coccinellidae and Anthribidae), and parasitic wasps primarily in the hymenopteran families Encyrtidae and Eulophidae (Ben-Dov and Hodgson, 1997; Lambdin, 2008).

Larvae and adults of the coccinellid Hyperaspis signata have been reported to be effective predators of N. cornuparvum (Williams and Kosztarab, 1972).

Larvae of the syrphid Ocyptamus costatus were reported feeding on N. cornuparvum infesting Magnolia × soulangeana in Kentucky for the first time by Vanek and Potter (2010a,b); the ant Tetramorium caespitum constructed shelters over nymphs and adults, protecting them from attacks by O. costatus (Vanek and Potter, 2010a).

Means of Movement and Dispersal

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Long-distance dispersal of N. cornuparvum is likely to result from the movement of infested plant material (e.g. nursery stock) as part of the plant trade. Local dispersal is limited because the adult females are immobile and the first-instar nymphs (crawlers) often remain near to their mother; new infestations of the pest may be started by crawlers being carried inadvertently on the feet of birds (Herms and Nielsen, 2004) or being actively transported by ants (Vanek and Potter, 2010b) from one plant to another. Crawlers may wander between plants that are touching, or be dispersed passively by the wind.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Botanical gardens and zoos Yes Yes
HitchhikerCan be carried on the feet of birds and by ants Yes Herms and Nielsen, 2004; Vanek and Potter, 2010b
Horticulture Yes Yes
Nursery trade Yes Yes
Self-propelledCrawlers may wander between plants that are touching Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Host and vector organismsCan be carried on the feet of birds and by ants Yes Herms and Nielsen, 2004; Vanek and Potter, 2010b
Plants or parts of plants Yes Yes
Wind Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark adults; nymphs Yes Pest or symptoms usually visible to the naked eye
Stems (above ground)/Shoots/Trunks/Branches adults; nymphs Yes Pest or symptoms usually visible to the naked eye

Impact Summary

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CategoryImpact
Environment (generally) Negative

Impact

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N. cornuparvum is a pest of wild and ornamental Magnolia in the USA (Williams and Kosztarab, 1972) and southern Ontario (Paiero et al., 2003). High populations of N. cornuparvum cause stress to plants by consuming large quantities of energy-rich phloem sap. This can result in a reduction in foliage and flower production, with symptoms such as small yellowing leaves, twig and branch dieback, and a thinning canopy. Heavy infestations can kill even mature plants. Although outbreaks of the pest can be sudden, plants can generally tolerate low to moderate infestations fairly well, providing time for control measures to be implemented before severe damage is incurred (Herms and Nielsen, 2004).

N. cornuparvum excretes large quantities of sugary honeydew, which coats twigs, leaves and other objects beneath feeding sites. The honeydew deposits can be colonized by sooty mould, which in extreme cases can interfere with photosynthesis of the plant by blocking light and air from the leaves. Honeydew and sooty mould are unsightly and can fall on to and damage objects beneath the affected plants. Other insects, such as ants, flies and wasps, are attracted to the honeydew as a food source, and these can create a nuisance (Hoover, 2002; Herms and Nielsen, 2004; Vanek and Potter, 2010b).

A scale insect believed to be N. cornuparvum was reported damaging a population of the endangered plant Sesbania tomentosa on Kauai, Hawaii, in August 2004. Almost all of the larger plants (1.5 to 2 m) were killed by the infestations, leaving smaller, younger plants, which produced fewer seeds and were more likely to be run over by all-terrain vehicles. Immature plants appeared to be less susceptible to N. cornuparvum (US Fish and Wildlife Service, 2010).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Sesbania tomentosaNational list(s) National list(s); USA ESA listing as endangered species USA ESA listing as endangered speciesHawaiiHerbivory/grazing/browsingUS Fish and Wildlife Service, 2010

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Gregarious
Impact outcomes
  • Host damage
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Herbivory/grazing/browsing
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field

Detection and Inspection

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For effective management of N. cornuparvum, a monitoring programme to detect early infestations is essential. Plants should be inspected regularly for the insects and for symptoms of infestation, e.g. brown exoskeletons of the previous generation of females, overwintering nymphs on twigs and branches, attendant ants, and the presence of honeydew and sooty mould on and beneath plants in the spring. A hand lens may be required to detect overwintering nymphs because of their small size (Herms and Nielsen, 2004).

Similarities to Other Species/Conditions

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Specimens of N. cornuparvum can easily be confused with tuliptree scale (Toumeyella liriodendri), an important pest of tuliptree (Liriodendron tulipifera), Magnolia and occasionally linden (Tilia spp.) (Kondo and Williams, 2008; Hoover, 2014; Shetlar and Andon, 2015); this has led to doubt about some field identifications (Ray and Williams, 1983). Adult females of T. liriodendri tend to be smaller (2.5–4.5 mm long) than those of N. cornuparvum (4.3–12.4 mm long) (Kondo and Williams, 2008). Authoritative identification requires the study of slide-mounted adult females under a compound light microscope. Adult female N. cornuparvum can be distinguished from other scale insects by the dense pattern of small 8-shaped pores on the dorsal derm (absent in Toumeyella liriodendri), and by having reduced legs and antennae (Williams and Kosztarab, 1972; Hamon and Williams, 1984). Adult males of N. cornuparvum can only be separated from those of T. liriodendri by comparing the length of antennal segments III–V and the metatibia in relation to other body structures (Giliomee, 1997).

Prevention and Control

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Cultural Control and Sanitary Measures

N. cornuparvum tends to attack stressed plants, so it is important to keep plants as healthy as possible by following a recommended fertilization programme and watering regime; however, high levels of fertilization can promote scale build up and should be avoided.

Physical/Mechanical Control

In low infestations, adult female scales can be removed in mid-summer (July) by hand or with a stiff brush before the appearance of crawlers. Heavily infested branches should be pruned back and destroyed (Herrick, 1931; Townsend, 2005; Knox et al., 2012). Low populations on one or a few branches can be removed by pruning, without adversely affecting the growth habit of the plant (Herms and Nielsen, 2004).

The use of physical barriers and insecticides to prevent ants from defending the pest against natural enemies is described below under 'IPM'.

Biological Control

In the eastern USA, natural enemies do not give effective control of high populations of N. cornuparvum, which is unusual for a native insect pest (Herms and Nielsen, 2004). One of the reasons for this may be protection by ants. Ants commonly attend scale insects, using the honeydew they produce as a source of sugar and nutrients. Attendant ants will defend the scale from its natural enemies, and provide sanitation by removing honeydew and dead individuals. The use of physical barriers and insecticides to prevent ants from defending the pest against natural enemies is described below under 'IPM'.

Chemical Control

Current direct control methods of N. cornuparvum rely on the use of conventional insecticides and horticultural oils, but timing is critical because the waxy covering on the scales protects them from contact insecticides and horticultural oils during much of the growing season. Dormant-season horticultural oils can be effective against overwintering nymphs when applied to Magnolia stems in the spring just prior to bud break, usually in about April (Herms and Nielsen, 2004; Townsend, 2005; Klass & Johnson, 2012).

Applications of broad spectrum insecticides during the growing season can give good control but are best avoided because of their negative impact on natural enemies. In a field study in Connecticut, a malathion emulsion applied on 11 April gave complete control of N. cornuparvum infestations on M. stellata by 10 May and was not damaging to the trees (Schread, 1961). As an alternative to foliar sprays, applications of the systemic insecticide imidacloprid as a drench around the roots of infested plants can be effective when applied before the appearance of crawlers. A field study in Ohio showed that soil drenches with imidacloprid on 1 May 2003 gave good control of high infestations of N. cornuparvum (Herms and Nielsen, 2004). Azadirachtin, neem seed oil, horticultural ‘summer’ oil and insecticidal soap are registered for use against soft scale insects in the USA and are less harmful to beneficial insects than conventional insecticides (Knox et al., 2012; Camacho and Chong, 2015; Smith et al., 2015).

The most effective time to spray contact insecticides is in late summer and autumn (late September/October), when the crawlers are active and before they develop their protective waxy covering. Insecticidal soap and horticultural oil can be effective, but because they lack residual activity they need to be applied every 7–10 days. Natural and synthetic insecticides (e.g. acephate, azadirachtin, carbaryl, lambda-cyhalothrin, dimethoate, esfenvalerate, malathion and permethrin) have longer residual activity and fewer applications are required (Townsend, 2005).

The use of physical barriers and insecticides to prevent ants from defending the pest against natural enemies is described below under 'IPM'.

Host Resistance

In field studies in Kentucky on host plant resistance to N. cornuparvum, the native species Magnolia grandiflora ‘Little Gem’ and M. virginiana were found to be resistant, while the native M. acuminata and non-native species M. liliiflora ‘Jane’, M. stellata ‘Royal Star’ and M. × loebneri ‘Merrill’ were susceptible to the pest (Vanek and Potter, 2009).

IPM

In Hawaii, an integrated pest management approach was proposed for the control of N. cornuparvum on Sesbania tomentosa, begining with treatment of affected plants with diatomaceous earth (a non-toxic pesticide), followed by the application of an insect growth regulator, and finishing with quarterly applications of a systemic insecticide to the plant roots to protect against future infestations.

The scale can be controlled indirectly by excluding attendant ants from the host plants. In Kentucky, Vanek and Potter (2010b) carried out field studies to evaluate ant exclusion as a means of suppressing two scale species, N. cornuparvum and Eulecanium cerasorum. Ants were excluded from Magnolia stellata plants by applying a physical barrier to the trunk at a height of 1 m in the spring, and spraying the lower 0.5 m of the trunk with the pyrethroid insecticide bifenthrin. Ten ant species were found tending N. cornuparvum in control treatments. Ant exclusion led to an 82% reduction in the number of N. cornuparvum reaching the adult stage after one year. Relatively few predators were observed in the study. It is concluded that the application of a simple trunk band to exclude ants has potential to increase scale insect mortality from natural enemies and to suppress infestations of the scale to below economic levels.

References

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Beardmore T; Loo J; McAfee B; Malouin C; Simpson D, 2006. A survey of tree species of concern in Canada: the role for genetic conservation. Forestry Chronicle, 82(3):351-363. http://www.nrc.ca/cisti/journals/tfc/TFC.html

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16/11/2015: Original text by:

Angela Whittaker, consultant, UK.

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