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Stictococcus vayssierei
(cassava brown root scale)

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Datasheet

Stictococcus vayssierei (cassava brown root scale)

Summary

  • Last modified
  • 20 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Stictococcus vayssierei
  • Preferred Common Name
  • cassava brown root scale
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • S. vayssierei is a scale insect found in Equatorial Africa. It feeds on the root system of cassava (Manihot esculenta), and can cause leaf-fall, wilting, tip dieback and ultimately death of cassava plants (

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Identity

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Preferred Scientific Name

  • Stictococcus vayssierei Richard, 1971

Preferred Common Name

  • cassava brown root scale

International Common Names

  • English: African root and tuber scale; brown root scale insect of cassava; cassava brown root scale insect; cassava root mealybug; root mealybug; root scale

EPPO code

  • STCCVA

Summary of Invasiveness

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S. vayssierei is a scale insect found in Equatorial Africa. It feeds on the root system of cassava (Manihot esculenta), and can cause leaf-fall, wilting, tip dieback and ultimately death of cassava plants (Ngeve, 2003a; Williams et al., 2010). Plants that develop normally may exhibit small mature tuberous roots that become covered in scales, making them unsuitable for sale (Ngeve, 2003a). S. vayssierei can cause yield losses of up to 100% and could pose a major threat to cassava production in Central Africa if strong control measures are not taken to control its spread (Ngeve, 2003a; Lema et al., 2004). The species could also present a quarantine threat to other parts of the world where cassava is produced, such as parts of southern Asia.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Hemiptera
  •                         Family: Stictococcidae
  •                             Genus: Stictococcus
  •                                 Species: Stictococcus vayssierei

Notes on Taxonomy and Nomenclature

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Richard (1976) stated that the three species previously plaecs in the genus Stictococcus were three genera: Stictococcus sensu stricto; Parastictococcus; and Hockiana.

S. vayssierei is in the genus Stictococcus sensu stricto, along with seven other species, including Stictococcus sjostedti (the type species), S. formicarius, S. intermedius and S. pujoli.

Description

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S. vayssierei is the only known hypogeal (below-ground) species in the family Stictococcidae (Tindo et al., 2006). It is a Sternorrhynchan with incomplete metamorphosis. Ngeve (2003a) described the males as rare and the more common adult female as dark-red, circular and flattened. In contrast, Tindo et al. (2006) described the adult females as brown and the first and second instars as purple-red.

The eggs are laid in wax threads secreted underneath the body, where they are protected and hatch into cream-white first-instar nymphs (Ngeve, 2003a).

Three developmental stages have been observed in the females: two immature instars and an adult stage (Tindo et al., 2006). Ngeve (2003a) and Tindo et al. (2006) agreed that there is no pupal stage in the female.

The body size and degree of sclerotization of the dorsal line increases with the development stage. The first instar lacks white waxy secretions, but these secretions are observed on the basal periphery of the second instar and on the dorsum and periphery of the adult females (Tindo et al., 2006).

Authoritative identification requires study of slide-mounted adult females under a compound microscope. Ngeve (2003a) provided a description of S. vayssierei and should be consulted for further details. In the slide-mounted adult female, the dorsal depressions in S. vayssierei are very shallow and sometimes difficult to locate, whereas in all other species of Stictococcus the dorsal depressions are much more conspicuous. (Williams et al., 2010).

Distribution

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In describing the genus Stictococcus, Williams et al. (2010) stated that, although the damage by S. vayssierei has only been reported recently, the species has probably been present but unnoticed for some time because of its subterranean habit. In the literature, S. vayssierei is described as ‘from Cameroon and neighbouring Central African countries’ (Capinera, 2008); however, individual citations have only been found for Cameroon and DRC, and are lacking for neighbouring Central African countries.

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.

Last updated: 10 Jan 2020
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

CameroonPresent, Widespread
Central African RepublicPresent
Congo, Democratic Republic of thePresent, Widespread
Congo, Republic of thePresent, Widespread
Equatorial GuineaPresent
GabonPresent
UgandaPresent

Risk of Introduction

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In a seven-year study of S. vayssierei in Cameroon, Ngeve (2003a) stated that this pest is likely to become an epidemic if strong control measures are not taken to control the spread, given that there are ‘poorly enforced quarantine regulations,’ and that there is unrestricted movement of vegetative planting stakes between African countries. 

Habitat

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S. vayssieri is found in cultivated land in equatorial climates in Cameroon and DRC. In southern Cameroon, significantly more S. vayssierei were found in nine-month-old cassava cuttings (68 +/- 12.4) than in well-cleared fields, where litter was burned and the ground was ploughed (24 +/- 8) (Dejean and Matile-Ferrero, 1996).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial ManagedCultivated / agricultural land Principal habitat Harmful (pest or invasive)

Hosts/Species Affected

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S. vayssierei feeds on the root system of cassava (Manihot esculenta), affecting tuber formation of the plant (Williams et al., 2010); however, there is evidence to suggest either polyphagy or involvement of more than a single scale species (Tindo et al., 2006). Sixteen plant species belonging to 13 families have been identified as hosts of S. vayssierei in the Congo basin (Tindo et al., 2009; see Host Plants/Crops Affected), but this may reflect the involvement of more than one species, as yet unidentified. It is thought that native Dioscorea species may play an important role in maintaining Stictococcus populations during long fallows and in secondary and primary forests. Cassava, an exotic plant in this area, may contribute to the growth of S. vayssierei in fallows less than 8 years old (Tindo et al., 2009).

Host Plants and Other Plants Affected

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Plant nameFamilyContextReferences
Aframomum danielliiZingiberaceaeOther
Chromolaena odorata (Siam weed)AsteraceaeOther
Costus aferZingiberaceaeOther
Dioscorea (yam)DioscoreaceaeOther
Elaeis guineensis (African oil palm)ArecaceaeOther
Haumania danckelmanianaMarantaceaeOther
Lasimorpha senegalensisArecaceaeOther
Manihot dichotomaEuphorbiaceaeOther
Manihot esculenta (cassava)EuphorbiaceaeMain
Musa (banana)MusaceaeOther
Palisota hirsutaCommelinaceaeOther
Talinum fruticosumPortulacaceaeOther
Xanthosoma sagittifolium (elephant ear)AraceaeOther

Growth Stages

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Fruiting stage, Vegetative growing stage

Symptoms

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Young feeder roots of germinating cassava cuttings are attacked by both the nymphs and adults of S. vayssierei. The feeding damage causes premature leaf-fall, wilting, tip dieback and ultimately results in death. Those plants that are not attacked until later develop normally and tuberize; however, they exhibit small mature tuberous roots and become covered in scales, making them unsuitable for sale (Ngeve, 2003a).

List of Symptoms/Signs

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SignLife StagesType
Growing point / dieback
Leaves / abnormal leaf fall
Leaves / wilting
Roots / external feeding
Roots / reduced root system
Whole plant / plant dead; dieback

Biology and Ecology

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Reproductive biology

S. vayssierei reproduces sexually and was recorded as being viviparous by Ambe et al. (1999); however, Ngeve (2003a) reported that eggs are laid in wax threads secreted underneath the body, where they are protected and hatch into cream-white first-instar nymphs.

Activity patterns

S. vayssierei usually appears in clusters or aggregations on the subterranean parts of host plants (Ambe et al., 1999).

Associations

S. vayssierei is attended by the ground-nesting ant Anoplolepis tenella. A study by Kuate et al. (2008) it was found that S. vayssierei was the hemipteran most commonly tended by A. tenella in southern Cameroon. Furthermore, Dejean and Matile-Ferrero (1996) reported that S. vayssierei cannot survive without this association.

Environmental requirements

Field populations of S. vayssierei appear to be influenced by season (Tchuanyo et al., 2000).  Ngeve (2003a,b) reported a more severe infestation of S. vayssierei in the dry season compared to the wet, and on flat ground compared to when cassava was planted on ridges. In Cameroon, S. vayssierei is limited to the southern part of the country, which is in the semi-humid zone with a bimodal rainfall pattern (Tchuanyo et al., 2000).

In general, severe infestations occur in lateritic and clayey soils, in fields of depleting fertility and in land where soil preparation is shallow, or planting has been carried out on the flat (Ngeve, 2003a). S. vayssierei is rarely found in newly opened forest farms or monocropped cassava plots (Ngeve, 2003a).

Climate

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ClimateStatusDescriptionRemark
Aw - Tropical wet and dry savanna climate Preferred < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])

Means of Movement and Dispersal

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Natural dispersal

Scale insects move during the crawler stage and as adult males. Newly hatched crawlers move over plants to locate suitable feeding positions. Ants, specifically Anoplolepis tenella Santschi, are the principal agents for the dispersal of S. vayssierei in southern Cameroon (Dejean & Matile-Ferrero, 1996).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Crop production Yes Yes Ngeve (2003a)

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Plants or parts of plants Yes Yes Ngeve (2003a)

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bulbs/Tubers/Corms/Rhizomes arthropods/adults; arthropods/larvae Yes Pest or symptoms usually visible to the naked eye

Impact Summary

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CategoryImpact
Economic/livelihood Negative

Economic Impact

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Ngeve (2003a) stated that S. vayssierei is a ‘major threat to cassava production in Cameroon and neighbouring Central African countries’. It can cause yield losses in cassava of up to 100% (Lema et al., 2004). 

Social Impact

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Cassava (Manihot esculenta) is a major source of carbohydrates and extensively cultivated in tropical and subtropical regions. It is a major staple food source in developing countries, particularly in drought conditions, providing a basic diet to over half a billion people (FAO, 1995). Given this important status, it follows that any threat to cassava production, such as S. vayssierei, will have a negative impact on the lives of those who rely on this crop as a source of income and nutrition.

Risk and Impact Factors

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Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Capable of securing and ingesting a wide range of food
  • Gregarious
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
  • Negatively impacts livelihoods
  • Threat to/ loss of native species
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally

Similarities to Other Species/Conditions

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The dorsal depressions in S. vayssierei are very shallow and sometimes difficult to locate, whereas in all other species of Stictococcus the dorsal depressions are much more conspicuous (Williams et al., 2010). S. vayssierei is similar to S. sjostedti, but has more slender bidentate marginal processes; thicker marginal spines; dorsal spines differently shaped; many glands in the pleural zone; a bifid spine on each of segments 3 and 4 of the antenna, and on the dorsal face of the tibia; the tarsus longer than the tibia, and more slender tarsal digitules than S. sjostedti (Richard, 1971). The ventral marginal setae of S. vayssierei are bullet-shaped, as in S. formicarius, but the latter species possesses flower-shaped dorsal setae that are absent from S. vayssierei.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Public awareness

In a survey of farmers in cassava-producing zones in Cameroon, Poubom et al. (2005) found that S. vayssierei was only considered to be important in the semi-humid forest zone. However, farmers producing cassava chips in the humid forest zone of Cameroon considered S. vayssierei to be one of the most important constraints in this type of production (Essono et al., 2008).

Cultural control and sanitary measures

Ngeve (2003b) studied the effect of S. vayssierei on cassava production in Cameroon and reported that when cassava was intercropped with maize and groundnuts, infestation by S. vayssierei was more severe compared to when cassava was planted alone. Therefore it is suggested that monocropping is used in areas where the impact of S. vayssierei is severe. However, as mixed cropping is widespread in Africa and used by farmers to insure against crop failure (Ngeve, 2003a), a change in approach for cassava production would be required, especially given that monocropping is one of few control measures available for this pest.

Tindo et al. (2009), working in the Congo basin, suggested that host plants of S. vayssierei from non-crop vegetation should be destroyed and removed to reduce pest infestations and improve cassava yields.

Planting date has also been found to affect incidence and population dynamics of S. vayssierei. In a study carried out by Ambe et al. (1999) in central and southern Cameroon, it was found that higher densities of this pest were generally recorded during the dry season. The start of the main rainy season (April to May) was found to be the most appropriate period for planting cassava, because this meant that the more susceptible growth stages of the crop did not coincide with the period of high pest infestations.

Planting cassava on ridges rather than on the flat results in improved plant vigour and root yield by approximately 22% (Capinera, 2008).

Biological control

According to Ngeve (2003b), biological control agents such as endomycorrhizae should be studied to determine their usefulness in pest control in Cameroon farming conditions.

Chemical control

Cuttings should be treated with insecticidal bioproducts before planting to reduce the impact of the pest (Ngeve, 2003b).

Host resistance (incl. vaccination)

Lema et al. (2004) investigated six cassava genotypes for their resistance to S. vayssierei. The study included using NPK fertilizer as a component of pest control. Three of the genotypes showed potential because infestations of this pest were delayed on them, with no scales present on them 6 months after planting. The application of fertilizer significantly increased the density of the scale population on an improved clone ‘F100,’ as well as plant height of F100 and a local DRC clone, ‘Kileba’. There was no significant effect on the number of tuberous roots and root yield on F100 or Kileba with fertilizer application.

In a study by Ngeve (2003b), the spread and severity of S. vayssierei from 1990 to 1998 at five sites in the sub-humid forest region of Cameroon was investigated using five cassava genotypes. It was found that the improved clones were more tolerant of S. vayssierei than the local variety.

References

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Ambe JT; Ntonifor NN; Awah ET; Yaninek JS, 1999. The effect of planting dates on the incidence and population dynamics of the cassava root scale, Stictococcus vayssierei, in Cameroon. International Journal of Pest Management, 45(2):125-130.

CABI/EPPO, 2015. Stictococcus vayssierei. [Distribution map]. Distribution Maps of Plant Pests, No.December. Wallingford, UK: CABI, Map 802.

Capinera JL, 2008. Encyclopedia of entomology. Volume 4, S-Z, Ed. 2 [ed. by Capinera, J. L.]. Heidelberg, Germany: Springer-Verlag GmbH, lxiv + 3225-4346 pp.

Dejean A; Matile-Ferrero D, 1996. How a ground-dwelling forest ant species favors the proliferation of an endemic scale insect (Hymenoptera: Formicidae; Homoptera: Stictococcidae). Sociobiology, 28(2):183-195.

Essono G; Ayodele M; Foko J; Akoa A; Gockowski J; Ambang Z; Bell JM; Bekolo N, 2008. Farmers' perceptions of practices and constraints in cassava (Manihot esculenta Crantz) chips production in rural Cameroon. African Journal of Biotechnology, 7(22):4172-4180.

FAO, 1995. Dimensions of need: an atlas of food and agriculture. 128 pp.

Kuate AF; Tindo M; Hanna R; Kenne M; Goergen G, 2008. Foraging activity and diet of the ant, Anoplolepis tenella Santschi (Hymenoptera: Formicidae), in southern Cameroon. African Entomology, 16(1):107-114.

Lema KM; Tata-Hangy K; Bidiaka M, 2004. Management of African root and tuber scale using improved cassava genotypes and mineral fertilisers. African Crop Science Journal, 12(3):217-222.

Lutete D; Tata-Hangy K; Kasu T, 1997. Occurrence in Zaire of Stictococcus vayssierei, a pest on cassava (Manihot esculenta). (Présence au Zaire de Stictococcus vayssierei (Homoptera, Sticticoccidae), un ravageur du manioc (Maniot esculenta).) Journal of African Zoology, 111(1):71-73.

Ngeve JM, 2003a. The cassava root mealybug (Stictococcus vayssierei Richard) [Hom: Stictococcidae]: present status and future priorities in Cameroon. African Journal of Root and Tuber Crops, 5(2):47-51.

Ngeve JM, 2003b. The cassava root mealybug (Stictococcus vayssierei Richard) (Homoptera: Stictococcidae): a threat to cassava production and utilization in Cameroon. International Journal of Pest Management, 49(4):327-333.

Poubom CFN; Awah ET; Tchuanyo M; Tengoua F, 2005. Farmers' perceptions of cassava pests and indigenous control methods in Cameroon. International Journal of Pest Management, 51(2):157-164.

Richard C, 1976. Revision of the group of Stictococcus, and the creation of new taxa (Homoptera, Coccoidea). (Revision du groupe des Stictococcus, et creation de taxa nouveaux (Homoptera, Coccoidea).) Annales de la Societe Entomologique de France, 12(4):653-669.

Tchuanyo M; Huis Avan; Lenteren JCvan, 2000. Distribution, incidence and abundance of the cassava brown root scale insect, Stictococcus vayssierei, in Cameroon. Tropical Science, 40(1):20-24.

Tindo M; Doumtsop A; Goergen G; Hanna R, 2006. Morphological description and illustration of female developmental stages of Stictococcus vayssierei (Homoptera: Stictococcidae). International Journal of Tropical Insect Science, 26(2):126-133.

Tindo M; Hanna R; Goergen G; Zapfack L; Tata-Hangy K; Attey A, 2009. Host plants of Stictococcus vayssierei Richard (Stictococcidae) in non-crop vegetation in the Congo basin and implications for developing scale management options. International Journal of Pest Management, 55(4):339-345.

Williams DJ; Matile-Ferrero D; Miller DR, 2010. A study of some species of the genus Stictococcus Cockerell (Hemiptera: Sternorrhyncha: Coccoidea: Stictococcidae), and a discussion on Stictococcus vayssierei Richard, a species injurious to cassava in Equatorial Africa with a description of a new species from Nigeria. Zootaxa, 2527:1-27. http://www.sel.barc.usda.gov/coccoidea/Sticto.pdf

Contributors

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29/05/14 Original text by:

Claire Beverley, CABI, UK

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