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CASSAVA MEALYBUG

 

Phenacoccus manihoti Matile-Ferrero -- Pseudococcidae

 

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A major food source for over 300 million people in tropical regions of the world, cassava is an important root crop (Bellotti & Schoonhoven 1985).  Most production (80%) is concentrated in Brazil, Indonesia, Nigeria, Zaire, India and Thailand.  This plant is native to tropical South America, and was introduced to the Congo basin in Africa in the early 16th Century (Cock 1985).  Although a perennial shrub reproducing vegetatively, cassava roots may be harvested 7 to 18 months after planting.  Roots are harvested by pulling the stems and uprooting the whole plant.

 

Mealybugs of the genus Phenacoccus have been recorded in association with cassava in South America and Africa.  Penaacoccus gossypii Towns. & Cock, P. grenadensis Green & Laing, and P. madeirensis Green are polyphagous, but P manihoti Matile-Ferrero appears specific to cassava and the only species capable of producing severe distortion of leaves.  Another South American species was separated from P. manihoti and described as P. herreni Cox & Williams (Cox & Williams 1981).  Mealybug damage seems to be a recent phenomenon, but one that is increasing in areas where it had not previously been found (Bellotti et al. 1985).  This new pest status results from an imbalance between the mealybug, the local cassava land race and the existing natural enemies.  The situation was particularly acute in Africa.  Phenacoccus manihoti was first discovered in Zaire in 1973 and spread into almost all other cassava growing areas of the continent.  The estimated losses caused by this species and another explosive pest, cassava green spider mites, Mononychellus spp., were estimated at $2.0 billion per year, and the pests affected an area about 5.5 million ha. (Neuschwander et al. 1984).

 

Control of the mealybug with natural enemies was attempted following its recognition as an immigrant species (Cox & Williams 1981).  Surveys for native natural enemies associated with P. manihoti in Gabon revealed that various guilds have incorporated the immigrant in their host or prey range, but none were greatly efficient (Boussienguet 1986).  The list included two primary parasitoids, four hyperparasitoids, nine predators and eight parasitoids of the predatory species (Neuenschwander et al. 1987).  Extensive explorations for natural enemies were conducted in South America.  Between 1977 and 1981 the Commonwealth Institute of Biological Control in collaboration with the International Institute For Tropical Agriculture surveyed the tropical areas of central and northern South America and found that the parasitoids Aenasius vexans Kerrich, Apoanagyrus diversicornis (Howard), and Anagyrus spp. seemed to be specific to the cassava mealybug (Cox & Williams 1981).  In 1980 a species of Diomus (Coccinellidae) was imported and released in experimental fields (IITA 1981, 1985), and one year later the encyrtid Epidinocarsis lopezi (DeSantis), collected in Paraguay by M. Yaseen, was imported to Nigeria and released at two sites.  The parasitoids were established and recovered from parasitized mealybugs.  (Lema & Herren 1985, Kogan et al. 1999).

 

The spread of E. lopezi was spectacular; by December of 1985 it had become established over 650,.000 km2 in 13 African countries (Neuenschwander et al. 1987).  Exclusion experiments and continuous monitoring demonstrated the efficiency of the parasitoid in regulating P. manihoti populations in Africa.  IITA (1985) reported that a significant reduction in population levels of the cassava mealybug had been observed in all regions colonized by E. lopezi.  In those areas, the mealybug was recorded at populations of 10-20 per terminal cassava shoot.  Prior to the establishment of the parasitoid peak populations in excess of 1,500 per shoot were common (IITA 1985).  The successful importation and establishment of E. lopezi gave further impetus to the biological control program at IITA, and additional species of parasitoids and predators are being released experimentally with various degrees of success (IITA 1987b, Kogan et al. 1992).

 

Detailed biological studies have been conducted on the coccinellid Hyperaspis raynevali Mulsant (Kiyindou & Fabres 1987), and the entomophthoraceous fungus Neozygites fumosa (Speare) Remaudiere & Keller (Le Ru 1986).  This successful biological control program of cassava mealybug in Africa is probably one of the best demonstrations of the potential of this tactic for IPM in short term crops.  However, other tactics are being used against this and other cassava pests, including breeding of plant resistance, cultural control and the selective use of pesticides (Cock & Reyes 1985).

 

 

REFERENCES:          [Additional references may be found at:   MELVYL Library ]

 

Bellotti, A. C. & A. van Schoonhoven.  1985.  Cassava pests and their control, p. 343-92.  In:  J. H. Cock & J. A. Reyes (eds.), Cassava: Research, Production and Utilization.  CIAT, Cali, Colombia.  745 p.

 

Bellotti, A. & A. van Schoonhoven.  1978.  Mite and insect pests of cassava.  Ann. Rev. Ent. 23:  39-67.

 

Bellotti, A. C., J. A. Reyes, J. M. Guerrero & A. M. Varela.  1985.  The mealybug and cassava green spider mite complex in the Americas:  Problems of and potential for biological control, p. 393-439.  In:  J. H. Cock & J. A. Reyes (eds.), Cassava: Research, Production and Utilization.  CIAT, Cali, Colombia.  745 p.

 

Cock, J. H.  1985.  Cassava:  A basic energy source in the tropics, p. 1-29.  In:  J. H. Cock & J. A. Reyes (eds.), Cassava: Research, Production and Utilization.  CIAT, Cali, Colombia.  745 p. 745 p.

 

Cock, J. H. & J. A. Reyes (eds.)  1985.  Cassava:  Research, Production and Utilization.  Preliminary Ed.  Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia.  745 p.

 

Cox, J. M. & D. J. Williams.  1981.  An account of cassava mealybugs (Hemiptera: Pseudococcidae) with description of a new species.  Bull. Ent. Res. 71:  247-58.

 

IITA.  1981.  Cassava mealybug - Biological control, p. 40-43.  In:  Research Highlights For 1980.  Intern. Inst. Trop Agric., Ibadan, Nigeria.  64 p.

 

IITA.  1985.  Dissemination, dispersal, and impact of E. lopezi - A natural enemy of the cassava mealybug, p. 35-39.  In:  Research Highlights For 1984.  Intern. Inst. Trop. Agric., Ibadan, Nigeria.  114 p.

 

Kiyindou, A. & G. Fabres.  1987.  Etude de la capacite d'accroissement chez Hyperaspis raynevali (Col.: Coccinellidae) predateur introduit au Congo pour la regulation des populations de Phenacoccus manihoti (Hom.: Pseudococcidae).  Entomophaga 32:  181-89.

 

Kogan, M., D. Gerling & J. V. Maddox.  1992. Enhancement of Biological Control in Transient Agricultural Environments In:  Bellows, T. S. & T. W. Fisher (eds.), Handbook of Biological Control:  Principles and Applications.  Academic Press, San Diego, New York.  1046 p.

 

Lema, K. M. & H. R. Herren.  1985.  Release and establishment in Nigeria of Epidinocarsis lopezi, a parasitoid of the cassava mealybug, Phenacoccus manihoti.  Ent. Exp. Appl. 38:  171-76.

 

Le Ru, B.  1986.  Epizootiology of the entomophthoraceous fungus Neozygites fumosa in a population of the cassava mealybug, Phenacoccus manihoti (Homoptera: Pseudococcidae).  Entomophaga 31:  79-90.