Phenacoccus manihoti
(cassava mealybug)

Pictures

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Identity

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Preferred Scientific Name

• Phenacoccus manihoti Matile-Ferrero, 1977

Preferred Common Name

• cassava mealybug

International Common Names

• Spanish: chinche harinosa de la yuca
• French: cochenille farineuse du manioc
• Portuguese: cochonilha da mandioca

Local Common Names

• Germany: Maniok-Schmierlaus

EPPO code

• PHENMA (Phenacoccus manihoti)

Summary of Invasiveness

Top of page Cassava mealybug spread across the width of Africa in a period of 16 years. Its accidental introduction damaged a staple crop that is particularly important in times of drought, during a time of drought, leading to famine (Herren and Neuenschwander, 1991).

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Hemiptera
•                         Suborder: Sternorrhyncha
•                             Unknown: Coccoidea
•                                 Family: Pseudococcidae
•                                     Genus: Phenacoccus
•                                         Species: Phenacoccus manihoti

Notes on Taxonomy and Nomenclature

Top of page The cassava mealybug was first reported in 1973 from the Kinshasa (Congo Democratic Republic [Zaire]) and Brazzaville (Republic of Congo) areas of Africa (Hahn and Williams, 1973; Sylvestre, 1973). The hitherto unknown insect was subsequently described and named in 1977 as Phenacoccus manihoti (Matile-Ferrero, 1977), originating from the neotropics. In the neotropics, the insect was first discovered in Paraguay in 1981 by A.C. Bellotti of CIAT. P. manihoti had earlier been confused with another mealybug species found on cassava in Guyana and northern Brazil. Whilst exploration for the natural enemies of P. manihoti continued, this other mealybug was identified as P. herreni (Cox and Williams, 1981). The taxonomic clarification greatly enhanced successful introductions and establishment of specific natural enemies of P. manihoti in an Africa-wide classical biological control programme.

Description

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Eggs

Eggs are oblong, golden yellow and enclosed in woolly ovisacs located at the posterior end of the adult females. Length and breadth measurements are 0.30-0.75 mm and 0.15-0.30 mm, respectively (Matile-Ferrero, 1978; Nwanze, 1978).

Larva

Antennae are 6-segmented in first instars and 9-segmented in subsequent instars. Body length and breadth measurements are, respectively, 0.40-0.75 mm and 0.20-0.30 mm for first instars/crawlers; 1.00-1.10 mm and 0.50-0.65 mm for second instars; 1.10-1.50 mm and 0.50-0.60 mm for third instars; and 1.10-2.6 mm and 0.50-1.40 mm for fourth instars/newly emerged adults (Matile-Ferrero, 1978; Nwanze, 1978).

Adult

Adult females of the cassava mealybug are ovoid, rose-pink and dusted with white, powdery wax; the eyes are relatively prominent, legs are well developed and of equal size (Matile-Ferrero, 1978). The mealybug's body segmentation is apparent. Body segments bear very short lateral and caudal white wax filaments in the form of swellings that produce a toothed appearance to the body outline.

- antennae often 9-segmented, occasionally with 7 or 8 segments
- denticle usually present on claw - body generally with 18 pairs of cerarii
- quinquelocular pores usually present on venter - dorsal and cerarian setae lanceolate
- cerarii usually each with 2 lanceolate setae and no auxillary setae, except on anal lobes

All of the microscopic features listed above as typical for genus Phenacoccus are present in P. manihoti. Other important characters of P. manihoti are:

- underside of head with 32-68 quinquelocular pores immediately anterior to the clypeolabral shield
- circulus 'ox-yoke' shaped
- no translucent pores on hind tibiae

The above characters will facilitate recognition of many Phenacoccus species, especially the economically important ones. The lanceolate setae are especially distinctive for this genus. Regional keys to mealybug faunas, such as the one provided by Williams and Granara de Willink (1992), should, however, be used to support an identification of Phenacoccus, as some species have only a few of the morphological features which are typically found in this genus. A useful key to identify P. manihoti may be found in Williams and Granara de Willink (1992).

Distribution

Top of page P. manihoti is indigenous to South America, where it is found in Argentina, Bolivia, Brazil, Colombia, Guyana and Paraguay. It was accidentally introduced from South America to the Congo Republic in 1973 (Herren and Neuenschwander, 1991). It has spread in Africa to practically all countries where cassava is grown, in a broad belt from West through to East Africa and down to the eastern edge of South Africa. A distribution map is provided by CIE (1993).

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.

Risk of Introduction

Top of page P. manihoti poses a threat to other cassava-growing regions of the world, such as Indonesia.

Accidental introduction to new territories is possible through the movement of infested living cassava material for propogative purposes through shipping or air transport/mail.

It may be advisable for plant quarantine services to regulate trade in fresh planting material of cassava from Africa and tropical South American countries to other tropical countries. Trade may still be possible through a system of inspection of source areas and pre-export certification of shipments being free of infection. Planting material should be inspected in the growing season previous to shipment and be found free of infestation. A phytosanitary certificate should guarantee absence of the pest from consignments of planting material.

Habitat

Top of page In Africa, P. manihoti survives and occurs on cassava in all agroecosystems where it has spread.

Hosts/Species Affected

Top of page The cassava mealybug strongly prefers cassava and other Manihot species; the other host crops and wild hosts are only marginally infested. Talinum triangulare, Croton and Poinsettia species are particularly suitable for laboratory rearing and experiments.

Records from other plants are apparently accidental (Herren and Neuenschwander, 1991). Although it has been collected on plants in various families, such as citrus and tomato, there is no evidence that it can survive for more than one generation on plants other than Manihot and perhaps certain other Euphorbiaceae (Williams and Granara de Willink, 1992).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Flowering stage, Fruiting stage, Seedling stage, Vegetative growing stage

Symptoms

Top of page In cassava and on Manihot glaziovii, the pest causes stunting, leaf distortion and loss, dieback and weakening of stems used for crop propagation. The insect does not cause any significant damage to its other known host crops/plants which may only serve as a temporary support for 'drifting' populations of the insect that fall on them.

List of Symptoms/Signs

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Biology and Ecology

Top of page Herren and Neuenschwander (1991) reviewed the biology of cassava mealybug. The life cycle has been studied in the Congo by Fabres (1980) and by Fabres and Boussiengue (1981). Mealybug populations begin to build up in February, and there are nine generations. The largest generation is that during the dry season. Population numbers drop at the onset of the rainy season, when many mealybugs are washed off the plant. Within cassava fields, this mealybug occurs in a markedly aggregated distribution pattern, which differs between seasons.

P. manihoti reproduces by parthenogenetic oviparity. The life cycle consists of an egg and four instar stages with the fourth being the adult mealybug. Various laboratory experimental results (Nwanze et al., 1979; Iheagwam, 1981; Lema and Herren, 1985; Le Rü and Fabres, 1987; Schulthess et al., 1987) summarize that the insect has a lower thermal threshold of 14.7°C, an optimal temperature of about 28°C, no development above 35°C and a net reproductive rate of about 500 eggs in an average life span of 20 days. Egg incubation lasts approximately 8 days and the insect usually dies 1-3 days after it ceases egg production (Nwanze, 1978). The average development period of egg to adult lasts for about 33 days. The most favoured sites for oviposition are terminal shoot tips, lower leaf surfaces and leaf petioles. The eggs hatch into crawlers (= first instars) and the insect moults thrice in its development to a fourth instar (= adult mealybug). Except for crawlers, all instars prefer the lower surfaces of fully expanded leaves (Nwanze, 1978) from where they move sluggishly to the stems and shoot tips. At low population densities, therefore, the insect is most abundant in the shoot tips (Schulthess et al., 1987; Neuenschwander and Hammond, 1988).

The stunted, distorted cassava tips which result from feeding offer a protective environment for the mealybugs which feed on the sap (Calatayud and Le Rü, 1997). Crawlers move actively within the plant, usually to upper leaf surfaces from where they easily get blown away by wind. Movement in air currents and transportation of infested stem planting material by man are the main methods by which the insect is dispersed over long distances.

Ants attending mealybugs for their honeydew are known to defend the pests from natural enemies that would otherwise attack them. They have been observed interfering with biological control of cassava mealybug in Ghana (Cudjoe et al., 1993).

Natural enemies

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Notes on Natural Enemies

Top of page In Africa, P. manihoti is attacked by the usual guild of polyphagous or oligophagous predators and parasitoids of mealybugs in Africa (Bartlett, 1978; Moore, 1988; Ben-Dov and German, 2003), which switched over to it as a new food source, and by indigenous entomopathogenic fungi, for example, Neozygites fumosa, which causes epizootics in the pest populations under warm and very humid conditions (Le Rü et al., 1985; Le Rü, 1986).

Prior to the introduction of Apoanagyrus lopezi (Hymenoptera: Encyrtidae) in Africa, lists of natural enemies of the pest were compiled for Congo (Matile-Ferrero, 1977; Fabres and Matile-Ferrero, 1980), Congo Democratic Republic (Nsiama Shè et al., 1984), Nigeria (Akinlosotu and Leuschner, 1981; Iheagwam., 1981) and Gabon (Boussienguet, 1986). Following the establishment of A. lopezi, the cassava mealybug food web was investigated over the whole continent and found to comprise about 130 species (Neuenschwander et al., 1987; Nsiama Shè, 1987; Biassangama et al., 1989). Many of the associated fauna are opportunistic and do not reproduce on the cassava mealybug; some are attracted more to the bunchy tops with the rich organic material from living and dead cassava mealybugs. Only about 20 species are common and seem to have some impact (Neuenschwander et al., 1987).

Wherever A. lopezi was established, it became the most important parasitoid and abundant natural enemy (Neuenschwander and Hammond, 1988; Hammond and Neuenschwander, 1990). Indigenous polyphagous hyperparasitoids adopt A. lopezi as an alternate host. The common hyperparasitoids in West Africa are Prochiloneurus insolitus and Chartocerus hyalipennis (Neuenschwander et al., 1987; Goergen and Neuenschwander, 1990; 1992; 1994). In Central Africa the hyperparasitoid P. aegyptiacus is usually most common (Fabres and Matile-Ferrero, 1980; Boussienguet, 1986; Neuenschwander et al., 1987; Biassangama et al., 1989). The most important predators are coccinellids, e.g., Hyperaspis spp., Exochomus sp., and Diomus sp., which usually occur at high densities of cassava mealybug (Fabres and Kiyindou, 1985; Boussienguet, 1986; Neuenschwander et al., 1987; Neuenschwander and Hammond, 1988; Stäubli Dreyer et al., 1997a,b). Results from olfactometer studies indicate that exotic and indigenous species of Diomus react more strongly to cassava mealybug, honeydew and exuviae than do indigenous Exochomus spp. (van den Meiracker et al., 1988).

Ants attending mealybugs for their honeydew are known to defend the pests from natural enemies that would otherwise attack them. They have been observed interfering with biological control of cassava mealybug in Ghana (Cudjoe et al., 1993).

Means of Movement and Dispersal

Top of page Natural dispersal

The dispersal stage of mealybugs is the first-instar crawler stage; these are often dispersed passively in the wind.

Vector transmission

Crawlers may also be carried passively by passing animals and people that brush past the host plant.

Agricultural practices

Harvesting infested plant material aids dispersal by scattering the crawlers into the air, where the wind may carry them away. Prunings of infested plants, and the clothing, tools and vehicles of agricultural workers can become contaminated with the crawlers and so aid in their dispersal.

Plant Trade

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Plant parts not known to carry the pest in trade/transport
Bulbs/Tubers/Corms/Rhizomes
True seeds (inc. grain)
Wood

Wood Packaging

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Impact Summary

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Impact

Top of page In 1973, P. manihoti was reported as an introduced arthropod species on cassava in Congo (Sylvestre, 1973; Matile-Ferrero, 1978) and Congo Democratic Republic (Hahn and Williams, 1973). Within a few years after these first reports, the insect became the major cassava pest and spread rapidly through most of the African cassava belt. By the end of 1986, for example, it had reached about 25 countries and covered 70% of the African cassava belt (Neuenschwander and Herren, 1988). In most countries the mealybug caused severe damage by stunting the growth points of cassava plants, sometimes totally defoliating the plants. Storage root yield losses of 84% have been reported (Nwanze, 1982). The pest-induced defoliation reduces availability of healthy leaves which are consumed as leafy vegetables in most of West and Central Africa. After the pest cripples plant growth, weed and erosion problems sometimes lead to total destruction of the crops. Additionally, pest-infested plants produce poor quality stem cuttings for use as planting material. The insect is more abundant and its damage severity is greater in the dry than in the wet season.

Examples of monetary values of damage are given by Norgaard (1988) and Neuenschwander (1990).

Zeddies et al. (2001) analysed the cost benefits of the biological control programme against cassava mealybug in Africa over a period of 40 years. Losses of cassava yield in the year of introduction were estimated at 80%; within 5 years, more tolerant varieties of cassava were cultivated and indigenous predators adapted to a new diet, so reducing annual losses to 20% (in rain forest) to 40% (in highlands and savanna).

Social Impact

Top of page The accidental introduction of P. manihoti to Africa damaged a staple crop that is particularly important in times of drought, during a time of drought, leading to famine (Herren and Neuenschwander, 1991).

Detection and Inspection

Top of page Colonies of this mealybug occur on the undersides of cassava leaves and on the shoot tips, and these will readily be seen during inspection. Minute crawlers, which may be present on plants before colonies are established, will only be detected by careful examination with the aid of a strong light and magnification. The plant tips are favoured feeding sites.

Similarities to Other Species/Conditions

Top of page P. manihoti is similar to P. madeirensis which also occurs on cassava. In P. madeirensis the body colour is greenish white and the ovisacs are much denser than those of P. manihoti. The presence of males in P. madeirensis is another distinguishing feature.

A very similar species, Phenacoccus herreni, is also common on cassava, but is yellow, produces males as well as females, and only occurs in South and Central America (Cox and Williams, 1981). Authoritative identification is difficult and should be done by an expert, using slide-mounted specimens. P. herreni may be identified using the key provided by Cox and Williams (1981) and Williams and Granara de Willink (1992).

Prevention and Control

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Biological Control

On the basis of the exotic origin and rapid spread of the cassava mealybug in Africa, classical biological control has been the main and most appropriate approach to the pest problem. Among several natural enemies introduced to combat the pest (Herren and Lema, 1982; Lema and Herren, 1985; Herren et al., 1987a; Neuenschwander and Zweigert, 1994), the solitary endophagous parasitoid Apoanagyrus lopezi, specific to P. manihoti, has been the most successful. Herren and Neuenschwander (1991) reviewed the biological control campaign against cassava mealybug in Africa. A. lopezi, collected from South America (Löhr and Varela, 1987; Löhr et al., 1988; Löhr et al., 1989; Löhr et al., 1990), has been the main natural enemy reared (Haug et al., 1987; Haug and Mégevand, 1989; Neuenschwander et al., 1989a, 1989b) and released across the cassava belt in Africa (Herren and Lema, 1982; Lema and Herren, 1985; Bird, 1987; Herren et al., 1987a,b). It was introduced to Nigeria in 1981 and is now established in at least 26 African countries (Ganga, 1984; Herren et al., 1987b; Korang-Amoakoh et al., 1987; Biassangama et al., 1988; Neuenschwander and Herren, 1988; Neuenschwander et al., 1989a, 1989b; Boussienguet et al., 1991; Hennessey et al., 1990; Herren and Neuenschwander, 1991; Neuenschwander and Zweigert, 1994). The biological and ecological impact of A. lopezi has been assessed in several laboratory and field experiments. In some studies, the results indicate a successful role of A. lopezi (Neuenschwander et al., 1986; Neuenschwander and Sullivan, 1987; Sullivan and Neuenschwander, 1988; Goergen and Neuenschwander, 1990; 1992; 1994; Cudjoe et al., 1992; 1993), whereas others are critical of reported success by A. lopezi (Fabres, 1981; Odebiyi and Bokonon-Ganta, 1986; Fabres et al., 1989; Iziquel and Le Rü, 1989; 1992; Le Rü et al., 1990; Souissi and Le Rü, 1997; 1998). Large-scale and sustained field studies have, however, recorded excellent biological control of the pest by A. lopezi (Neuenschwander and Madojemu, 1986; Hammond et al., 1987; Gutierrez et al., 1988a,b; Neuenschwander and Hammond, 1988; Neuenschwander and Gutierrez, 1989; Neuenschwander et al., 1989a, 1989b; van Alphen et al., 1989; Hammond and Neuenschwander, 1990; Neuenschwander et al., 1990; Gutierrez et al., 1993; Chakupurakal et al., 1994; Neuenschwander and Ajuonu, 1995; Neuenschwander, 1996). Ants attending mealybugs for their honeydew are known to defend the pests from natural enemies that would otherwise attack them. They have been observed interfering with biological control of cassava mealybug in Ghana (Cudjoe et al., 1993). It may be advisable to discourage ants in cassava fields if this becomes a problem. The economic impact of biological control of the cassava mealybug, mainly by A. lopezi, has been judged to be excellent (Norgaard, 1988a, b; Zeddies et al., 2001). Nominal costs of the biological control programme 1979-2013 were estimated at US$ 34.2 million, with the peak annual cost of the programme coming to US$ 5.2 million in 1985. The benefit to cost ratio of biological control by Apoanagyrus (Epidinocarsis) lopezi was calculated as at least 199:1. Where the soil is very infertile, however, biological control has been shown to be unsatisfactory, unless it can be complemented by cultural practices such as soil improvement (Neuenschwander et al., 1990; Le Rü et al., 1991; Schulthess et al., 1997) and host-plant resistance (Le Rü and Tertuliano, 1993; Tertuliano et al., 1993; Souissi and Le Rü, 1998). Biological control (particularly using the parasitoid Apoanagyrus lopezi) and the use of resistant varieties to control the pest are briefly described by Calatayud and Le Rü (1997). The coccinellid Hyperaspis notata is associated with the mealybugs P. manihoti and P. herreni on cassava in southern Brazil and the highlands of Colombia. It was brought to Africa to help control the accidentally introduced P. manihoti (Staubli-Dreyer et al., 1997). The parasitoids A. diversicornis, Allotropa sp., and the neuropteran predator Sympherobius maculipennis apparently failed to establish following their releases in Africa (Neuenschwander and Zweigert, 1994).

Organic Chemical Control

Immersion of cassava cuttings in manipueira (a liquid extract from cassava roots) for 60 minutes was found to significantly reduce infestation (Razafindrakoto et al., 1999). Mourier (1997) found that cassava leaves treated with a 1% neem kernel water extract (NKWE) were less attractive to first-instar cassava mealybug than untreated leaves, and those that started feeding died in the second instar. Three NKWE treatments at weekly intervals protected cassava against established early instar nymphs; however, some phytotoxicity was observed.

Host-Plant Resistence

Cassava contains two significant compounds whose levels increase in response to mealybug infestation. Cyanide content acts as a phagostimulant for the mealybug, whereas rutin has an antibiotic effect on the pest. It was found that the use of mulch and manure increased cassava resistance against mealybug infestation (Tertuliano et al., 1999). The use of resistant varieties to control the pest are briefly described by Calatayud and Le Rü (1997).

Cultural Control

Use of manure or other fertilizers can result in a reduction in the mealybug population because improved nutrition results in the production of larger parasitoid wasps with higher fertility levels (Schulthess et al., 1997). Mulch and fertilizer use also enhances the antibiotic properties of cassava against mealybug infestation (Tertuliano et al., 1999).

References

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Akinlosotu TA; Leuschner K, 1981. Outbreak of two new cassava pests (Mononychellus tanajoa and Phenacoccus manihoti) in southwestern Nigeria. Tropical Pest Management, 27(2):247-250

Alphen JJM van; Neuenschwander P; Dijken MJ van; Hammond WNO; Herren HR, 1989. Insect invasions: the case of the cassava mealybug [Phenacoccus manihoti] and its natural enemies evaluated. Entomologist, 108(1-2):38-55

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Ben-Dov Y, 1994. A systematic catalogue of the mealybugs of the world (Insecta: Homoptera: Coccoidea: Pseudococcidae and Putoidae) with data on geographical distribution, host plants, biology and economic importance. Andover, UK; Intercept Limited, 686 pp.

Ben-Dov Y; German V, 2003. ScaleNet, Maconellicoccus hirsutus. 27 November 2003. http://www.sel.barc.usda.gov/catalogs/pseudoco/Phenacoccusmanihoti.htm.

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Biassangama A; Ru B le; Iziquel Y; Kiyindou A; Bimangou AS, 1989. The insects associated with the cassava mealybug, Phenacoccus manihoti (Homoptera: Pseudococcidae) in Congo, five years after the introduction of Epidinocarsis lopezi (Hymenoptera: Encyrtidae). Annales de la Societe Entomologique de France, 25(3):315-320

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Chakupurakal J; Markham RH; Neuenschwander P; Sakala M; Malambo C; Mulwanda D; Banda E; Chalabesa A; Bird T; Haug T, 1994. Biological control of the cassava mealybug, Phenacoccus manihoti (Homoptera: Pseudococcidae), in Zambia. Biological Control, 4(3):254-262

Cox JM; Williams DJ, 1981. An account of cassava mealybugs (Hemiptera: Pseudococcidae) with a description of a new species. Bulletin of Entomological Research, 71(2):247-258.

Cudjoe AR; Neuenschwander P; Copland MJW, 1992. Experimental determination of the efficiency of indigenous and exotic natural enemies of the cassava mealybug, Phenacoccus manihoti Mat.-Ferr. (Hom., Pseudococcidae), in Ghana. Journal of Applied Entomology, 114(1):77-82

Cudjoe AR; Neuenschwander P; Copland MJW, 1993. Interference by ants in biological control of the cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae) in Ghana. Bulletin of Entomological Research, 83(1):15-22.

Dewi Sartiami; Watson GW; Mohamad Roff MN; Hanifah YM; Idris AB, 2015. First record of cassava mealybug, Phenacoccus manihoti (Hemiptera: Pseudococcidae), in Malaysia. Zootaxa, 3957(2):235-238. http://www.mapress.com/zootaxa/2015/f/z03957p238f.pdf

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Fabres G; Kiyindou A, 1985. Comparison of the biotic potential of two coccinellids (Exochomus flaviventris and Hyperaspis senegalensis hottentotta, Col. Coccinellidae), predators of Phenacoccus manihoti (Hom. Pseudococcidae) in the Congo. Acta Oecologica, Oecologia Applicata, 6(4):339-348

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Giga DP, 1994. First record of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae), from Zimbabwe. African Entomology, 2(2):184-185

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Goergen G; Neuenschwander P, 1992. A cage experiment with four trophic levels: cassava plant growth as influenced by cassava mealybug, Phenacoccus manihoti, its parasitoid Epidinocarsis lopezi, and the hyperparasitoids Prochiloneurus insolitus and Chartocerus hyalipennis. Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz, 99(2):182-190

Goergen G; Neuenschwander P, 1994. Chartocerus hyalinipennis (Hayat) (Hym.: Signiphoridae), a gregarious hyperparasitoid on mealybugs (Hom.: Pseudococcidae): biology and host range in West Africa. Mitteilungen der Schweizerischen Entomologischen Gesellschaft, 67(3-4):297-308

Gutierrez AP; Neuenschwander P; Alphen JJMvan, 1993. Factors affecting biological control of cassava mealybug by exotic parasitoids: a ratio-dependent supply-demand driven model. Journal of Applied Ecology, 30(4):706-721

Gutierrez AP; Neuenschwander P; Schulthess F; Herren HR; Baumgprtner JU; Wermelinger B; Lohr B; Ellis CK, 1988. Analysis of biological control of cassava pests in Africa. II. Cassava mealybug Phenacoccus manihoti. Journal of Applied Ecology, 25(3):921-940

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