''Phenacoccus manihoti'' is a mealybug insect species. In the early 1970s, the cassava mealybug ''P. manihoti'' was accidentally introduced to

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

.Neuenschwander, P., et al,. 1990. Biological Control of the cassava mealybug ''Phenacoccus manihoti'' (Hom., Pseudococcidae) by Epidinocarsis lopezi (Hym., Encyrtidae) in West Africa, as influence by climate and soil. Agriculture, Ecosystems and Environment. 32: 39 – 55 Within 15 years of its discovery, it had invaded most of West and Central Africa and was spreading to the East.Hennessey, R. D, et al,. 1990. Spread and current distribution of the cassava mealybug, ''Phenacoccus manihoti'' (Homoptera: Pseudococcidae), in Zaire. Tropical Pest Management. 36: 103 – 107. It soon became an important pest, and methods to control it became a topic of interest. The cassava mealybug was successfully suppressed at a continent-wide scale by the introduction of a specialist parasitic wasp, originally discovered in the mealybug's region of origin (i.e., Paraguay, Southern Brazil). This

biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also i ...

endeavor was awarded with the 1995

World Food Prize The World Food Prize is an international award recognizing the achievements of individuals who have advanced human development by improving the quality, quantity, or availability of food in the world. Conceived by Nobel Peace Prize laureate Nor ...

being handed to Swiss entomologist Hans Rudolf Herren.

Description

''P. manihoti'' is a type of mealybug. It is commonly called the cassava mealybug because it feeds on

cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively cultivated ...

. It is an oligophagous insect that demonstrates an

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

-like

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is c ...

feeding behavior.Calatayud, P. A. 2000. Influence of linamarin and rutin on biological performances of ''Phenacoccus manihoti'' in artificial diets. Entomologia Experimentalis et Applicata. 96: 81 – 86. ''P. manihoti'' reproduces by thelytokous

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

and goes through four in-star

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

l forms which have differing numbers of antennal segments.Le Ru, B., et al,. 1995. Antennal sensilla and their possible functions in the host-plant selection behavior of ''Phenacoccus manihoti'' (Matile-Ferrero) (Homoptera: Pseudococcidae). International Journal of Insect Morphology and Embryology. 24: 375 – 389. Mealybugs are noted for the production of dermal wax secretions.Cox, J. M. & Pearce M. J. 1983. Wax produced by dermal pores in three species of mealybug (Homoptera: Pseudococcidae). International Journal of Insect Morphology and Embryology. 12: 235 – 248. The body is covered with wax producing pores which have been well studied but the function of wax to particular species is based on speculation. Predictions about the function of dermal wax in the cassava mealybug suggest it is to prevent desiccation and to deter predators. The longer coils of wax secreted would be bitten first by a predator and give the cassava mealybug a chance to escape. Females have the highest fecundity on the first or second day of oviposition.Lema, K. M. & Herren, H. R. 1985. The influence of constant temperature on population growth rates of the cassava mealybug, ''Phenacoccus manihoti''. Entomologia Experimentalis et Applicata. 38: 165 – 169. The optimal temperature for populations of the cassava mealybug is between 20 and 30 degrees Celsius. The cassava mealybug has poor survivability during rainy season because it gets washed off the plant and drowns.Iheagwam, E. U. & Eluwa, M. C. 1983. The effects of temperature on the immature stages of the Cassava Mealybug, ''Phenacoccus manihoti'' Mat-Ferr. (Homoptera, Pseudococcidae). Deutsche Entomologische Zeitschrift. 30: 17 – 22.

Sensory structures

The cassava mealybug has similar host plant detection behavior to

aphids Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

.Renard, S., et al,. 1997. Recognition Behavior of the Cassava Mealybug ''Phenacoccus manihoti'' Matile-Ferrero (Homoptera: Pseudococcidae) at the Leaf Surface of Different Host Plants. Journal of Insect Behavior. 11: 429 – 450. It uses sight and smell to detect a possible host, once it lands, it walks along the leaf surface and uses specialized sensory organs to determine viability. After this, it penetrates the plant using a stylet and tests the phloem for quality and quantity. Generally the cassava mealybug can determine if a plant will be a suitable host within the first step of walking on the leaf surface. It damages the cassava plant by causing deformation, defoliation, and stunted growth which leads to the death of the plant.James, B. D. & Fofanah, M. 1992. Population growth patterns for ''Phenacoccus manihoti'' Mat-Ferr on cassava in Sierra Leone. Tropical Pest Management. 38: 89 – 92. The cassava mealybug uses antennae and receptors on the labium as a way to identify its host plant. The labium has thirty sensilla that include trichoid hairs and sensilla chaetica.Le Ru, B., et al,. 1995. Ultrastructure of sensory receptors on the labium of the cassava mealybug, ''Phenacoccus manihoti'' Matile Ferrero. Entomologia Experimentalis et Applicata. 77: 31 – 36. The trichoid hairs function as mechanoreceptors, while the sensilla chaetica or pegs serve as mechanoreceptors,

chemoreceptors A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorec ...

and olfactory organs. There are several types of sensilla chaetica. Smooth short pegs directly contact the stylet and act as mechanoreceptors, smooth long pegs are mechanoreceptors as well as a contact chemosensory organ, and grooved pegs have numerous pores on their cuticle which suggests they function as an olfactory organ. The cassava mealybug also uses antennal sensilla as a way to identify host-plants. The antenna are thought to be useful in detecting volatile substances given off by the plant. The antenna have similar ultrastructures that are found on the labium except studies showed that there was up to 58 sensilla on the antenna, which is more than what is found on the labium. The sensilla can work as mechanoreceptors, thermo-hygro receptors, chemoreceptors and olfactory sensory organs.

Damage

The cassava mealybug can destroy up to 54% of roots and 100% of leaves in locations of infestation. When it infests cassava it deteriorates the tissue mineral and nutrient contents. If the plant becomes stressed during dry season it is even more susceptible to infestation.

Control

Pesticides were used as an initial response to the cassava mealybug problem. Many different kinds were used and studied and they did seem to be effective, but they were costly.Atu, U. G. & Okeke, J.E,. 1981. Evaluation of insecticides for control of cassava mealybug (''Phenacoccus manihoti''). Tropical Pest Management. 27: 251- 253. The most effective pesticide tested was methidathion; in trials the infested cassava showed significant recovery.

Contrary to insecticide use, biological pest control provided a self-sustaining, cost-effective and environmentally-sound solution for mealybug suppression across the African cassava belt. The use of the introduced parasitoid ''Anagyrus lopezi'' proved to be a spectacular success story in the biological control of the cassava mealybug. The parasitoid attacks the second and third instar stages of the cassava mealybug. Within a few years of its release it covered the entire country, and within five years there were no high concentrations of the cassava mealybug present.Chakupurakal, J., et al,. 1994. Biological Control of the Cassava Mealybug , ''Phenacoccus manihoti'' (Homoptera: Pseudococcidae), in Zambia. Biological Control. 4: 254 – 262. The successful elimination of the cassava mealybug across the African continent increased cassava yields and improved farmer livelihoods, without any negative environmental side-effects. Biological control of the cassava mealybug generated economic benefits of over US$120 billion, averted widespread famine across subSaharan Africa and purportedly saved the lives of 20 million people.Maredia, M.K. and Raitzer, D.A., 2010. Estimating overall returns to international agricultural research in Africa through benefit‐cost analysis: a “best‐evidence” approach. Agricultural Economics, 41(1), pp.81-100.

This biological control effort was replicated in Southeast Asia, where ''P. manihoti'' had made its unfortunate arrival in 2008. The introduction of ''A. lopezi'' lowered mealybug infestation levels to considerable extent, restored cassava yields, exerted stabilizing effects on prices and inter-country trade of different cassava products - including starch.Wyckhuys, K.A., Zhang, W., Prager, S.D., Kramer, D.B., Delaquis, E., Gonzalez, C.E. and Van der Werf, W., 2018. Biological control of an invasive pest eases pressures on global commodity markets. Environmental Research Letters, 13(9), p.094005.

References

{{Taxonbar, from=Q7181310 Pseudococcidae Insects described in 1977