Mononychellus tanajoa
(cassava green mite)

The cassava green mite, M. tanajoa, is of Neotropical origin but was accidentally introduced to Africa in 1971 (Nyiira, 1972). By 1985, the pest had spread throughout the cassava belt of Africa (Yaninek and Heren, 1988). M. tanajoa affects the important annual crop cassava (Manihot esculenta) and can cause a reduction of about 50% in leaf weight, and up to 80% tuber yield loss (Shukla, 1976; Gutierrez et al., 1988; Pallangyo et al., 2004). M. tanajoa is mainly dispersed by human activity, whereby infested plant materials and contaminated media are transported over long distances. Natural dispersion by wind and water may also spread the cassava green mite. In areas where both the pest and host plant are exotic, there is no evidence that indigenous natural enemies are significant factors in limiting the mite population growth rates. M. tanajoa can feed and reproduce on other plant species (Moraes et al., 1995) and is reported as a quarantine pest (Delalibera et al., 1992; EPPO, 2009).

Like cassava, its primary host, M. tanajoa originated from the neotropics, where it occurs sporadically.

Due to the misidentification of the exotic mite M. progresivus as M. tanajoa in Africa, the distribution of M. tanajoa in this region requires careful scrutiny. Distribution data for M. tanajoa published from the 1970s to the mid 1990s during a time of taxonomic ambiguity may not be as accurate as more current references (Hicks, 2017).

For further references to Central American records, see Bolland et al. (1998).

Records of M. tanajoa in Antigua and Barbuda, Argentina, Chile, French Guiana, Peru, Suriname, Uruguay, Northern Mariana Islands and Micronesia (EPPO, 2014) published in previous versions of the Compendium are now considered unreliable (EPPO, 2016). 

A record of M. tanajoa in Australia (EPPO, 2014) published in previous version of the Compendium was based on an old record which is now considered to be erroneous. In 2016, Australian mite specialists confirmed the absence of M. tanajoa in Australia to the NPPO (EPPO, 2016).

Records of M. tanajoa in Florida (Pena et al., 1984) and Puerto Rico (Cruz, 1981) published in previous versions of the Compendium are considered invalid as they refer to M. caribbeanae, which was previously considered a synonym of M. tanajoa (Tuttle et al., 1977) but is now recognized as a separate species (Doreste, 1981).

In 2010, M. tanajoa was reported in Hainan, China (Lu et al., 2012), but the mite was incorrectly identified. Subsequent publications by Lu identify the species as M. mcgregor (Lu et al., 2014). Cassava green mite is not present in China (Parsa et al., 2015). M. tanajoa has not been reported in any of the Asian cassava-producing countries (Bellotti et al., 2012).

Korang-Amoakoh et al. (1987) described the species found in Ghana as “M. tanajoa sensu latu”, therefore the mite’s specific epithet was not verified. This record is unreliable as no current sources include Ghana in the distribution of M. tanajoa.

M. tanajoa has spread to almost all tropical countries where cassava is grown.

M. tanajoa is found on cassava (Manihot esculenta) and other plants in the genus Manihot, such as Manihot glaziovii and Manihot dichotoma (Bastos and Flechtmann, 1985; Ezulike and Egwuatu, 1993a). However, Moraes et al. (1995) reported that cassava green mite could feed and develop to the adult stage on Phaseolus vulgaris and also develop to the adult stage and lay eggs on the wild passion fruit Passiflora cincinnata. Several other hosts are listed in the catalogue by Bolland et al. (1998).

Tomato was previously listed as a host of M. tanajoa, but this host record was for M. caribbeanae, which is now recognized as a separate species (Doreste, 1981).

Common bean (Phaseolus vulgaris) is a conditional non-preferred host of M. tanajoa (Hicks, 2017).

The life history of M. tanajoa is typical of all tetranychids. Reproduction is arrhenotokous (Helle and Pijnacker, 1985). There are four active instars: a six-legged larva, two nymphal instars (protonymphs and deutonymphs) and an adult stage.

The biology of M. tanajoa, including the developmental time, fecundity and adult longevity depends on temperature, humidity, host plant and sex (Byrne et al., 1982b; Mesa et al., 1987; Yaninek et al., 1989a, c). Yaninek et al. (1989a) report that at 27°C, with relative humidity of 70% and a photoperiod of 12 hours light and 12 hours dark, the developmental times of egg, larva, protonymph and deutonymph on leaves of cassava (variety TMS 30572) were 5.4, 3.0, 1.1 and 2.8 days, respectively. At this temperature, typical of most areas in sub-Saharan Africa, the adult female mite lives for 11.6 days and lays an average of 62.8 eggs over a period of 9.8 days. The net reproduction rate reached a maximum of 43.2 progeny. Egg to adult developmental periods were estimated to be 21.3, 15.5, 12.3, 7.7 and 6.9 days at 20, 24, 27, 31 and 34°C, respectively. Yaninek and Gnanvossou (1993) reported that eggs, larvae and protonymphs had average fresh weights of 0.637, 0.625 and 1.013 µg respectively. Male and female deutonymphs had average weights of 1.209 and 2.715 µg, whereas male and female adults averaged 1.633 and 7.035 µg, respectively.

The availability of new foliage on cassava plants and the presence of rainfall are the major factors that determine the population dynamics of M. tanajoa in the field (Yaninek et al., 1989a, c). The population increases on new leaf growth during the early dry season (20-200 mites/leaf), but declines when defoliation and reduced leaf production follow drought. Prolonged rainfall also leads to a decrease in population (<1 mite/leaf) because the mites are washed off the plant.

Predatory insects and mites are the most abundant and important natural enemies of M. tanajoa. Most of the known insect predators are either opportunists or effective only at high mite populations. The most commonly encountered insect predators in the neotropics are in the families Coccinellidae, Staphylinidae, Lygaeidae, Chrysopidae, Syrphidae, Anthocoridae and Cecidomyiidae (Farias et al., 1981; Byrne et al., 1983) and the order Thysanoptera. Stethorus spp. and Holobus (=Oligota) spp. have been reared and released in a number of countries.

Mites of the family Phytoseiidae are the most important predators of M. tanajoa because they have a high capacity for predation, even at low prey densities and are also easy to rear. Bellotti et al. (1987) listed 46 phytoseiid species found in association with M. tanajoa on cassava in Colombia.

Environmental

• Biological control

General

• Research model

Genetic importance

• Gene source
• Test organisms (for pests and diseases)

M. tanajoa typically feeds on the underside of young leaves, starting along the veins and at the base of the leaves. Damage symptoms can be seen with the naked eye but eggs, crawlers or adults  are usually only visible under a light microscope. Examination of the underside of young leaves and growing terminals of cassava reveals the presence of this pest. Fresh sprouts from cassava stem cuttings may also harbour these mites and must be examined to prevent spread.

M. tanajoa is similar to the red spider mites (Tetranychus spp. and Oligonychus spp.). Although M. tanajoa is greenish/yellowish in appearance and the red spider mites are reddish in colour, all of them cause yellow specks (chlorosis) on leaves, especially along the main veins. However, red spider mites are larger than M. tanajoa and normally attack mature leaves lower down on the plants and cover the attacked leaves with webs.

The damage caused by M. tanajoa also looks similar to that caused by African cassava mosaic disease. Both cause leaf chlorosis, but the greenish-yellowish patches of African cassava mosaic disease are usually larger and severe leaf distortion is common.

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.

Regulatory Control

Close inspection of cutting materials and the use of clean certified cuttings may reduce the spread of M. tanajoa and delay the time of infestation of the cassava crop.

Cultural Control

Cultural control is limited owing to economic, technical and social constraints. Options include early planting at the onset of the rains to encourage vigorous growth and thereby increase tolerance to mite attack. Cassava plants aged 2-9 months are the most vulnerable to infestation.

The way a mite-infested cutting is planted influences the presence of the mites on the leaves soon after sprouting. Cuttings planted in a slanting position had mites on the leaves soon after sprouting, but those planted horizontally did not (Ezulike and Egwuatu, 1990). Ezulike and Egwuatu (1993b) reported that cassava intercropped with pigeon pea suffered less damage from M. tanajoa than that grown on a pure stand. They also found that cassava intercropped with pigeon pea in triple and double rows gave higher tuber yields than when it was alternated in a single row or in a pure stand.

Host-Plant Resistance

Certain attributes, such as leaf pubescence (Leuschner, 1982), have been claimed to confer tolerance to M. tanajoa. Some attempts have been made to identify mite-resistant cassava cultivars (Shukla, 1976; Santos et al., 1977; Byrne et al., 1982a,b; Markham and Robertson, 1987; Msabaha, 1984) but further studies including damage symptoms, tuber yields and disease resistance of the selected cultivars need to be carried out. Immunity to M. tanajoa is not known.

Biological Control

The importation of phytoseiids from the neotropics (especially from Colombia and Brazil) and their release into Africa began in 1984. In 1991, Amblyseius (=Neoseiulus) idaeus from north-eastern Brazil was reported to have persisted for over 18 months after release in Benin (Yaninek et al., 1991).

Toko et al. (1996) released the predator Amblyseius manihoti into a cassava field infested with M. tanajoa at the beginning of the dry season and recorded a 20% decrease in the numbers of M. tanajoa compared with control areas where there were no predators.

Herrera et al. (1994) studied the population dynamics of M. tanajoa and its predators Amblyseius limonicus and A. idaeus on cassava at three sites in Colombia between 1988 and 1990. The numbers of the phytoseiids increased in response to the population growth of M. tanajoa, but higher predator densities were observed when M. tanajoa densities were low. At one site (Pivijay), A. limonicus appeared at the peak population of M. tanajoa and suppressed the pest population, while itself persisting during the wet season in the absence of M. tanajoa. Compared with plots without predators, cassava plots with predators harboured less than 50% of the M. tanajoa population and produced double the fresh tuber yields.

The mite Typhlodromalus manihoti has been established in West Africa since its importation in 1989 from north-eastern Brazil (which is ecologically more similar to sub-Saharan Africa than is Colombia).

Typhlodromalus aripo was introduced from Brazil into West Africa to control M. tanajoa in 1993 (IITA, 1996). T. aripo has now spread, at times at a rate of 200 km/year, and established itself in more than 11 countries in Africa. M. tanajoa populations have dropped to less than 20/leaf, from more than 40/leaf before the introduction of T. aripo. Post release surveys conducted under farm field conditions in Tanzania reported a decline of M. tanajoa population densities from > 200 mites per leaf (before T. aripo introduction) to < 20 mites per leaf (Pallangyo et al., 2004). During a predator exclusion experiment, M. tanajoa population densities and damage severity were reduced by 64.3% and 45.3% respectively leading to an increase in cassava yield by up to 70% (Pallangyo et al., 2004). In Benin, this has led to a 30% increase in tuber yields, equivalent to a gain of $3 million per season.

The predatory insects Stethorus spp. and Holobus (=Oligota) spp. have been reared and released in a number of countries.

Among the pathogens, Neozygites spp. have shown the greatest potential for biological control. It has been reported to cause mortalities among M. tanajoa populations in Venezuela (Agudelo-Silva, 1986), Brazil (Delalibera et al., 1992), Colombia (Alvarez et al., 1993), Benin (Yaninek et al., 1996) and Kenya (Bartowski et al., 1988). The effect of abiotic factors on the ability of this fungus to cause epizootics among populations of M. tanajoa has been studied by Oduor et al. (1995a, b; 1996a, b; 1997a, b). Brazilian species are being compared with African strains to identify the ideal isolate for mass release in Africa.

Chemical Control

Most cassava is grown on a small scale by subsistence farmers with few resources. Lack of knowledge and finance makes the use of chemicals a non-sustainable option for controlling M. tanajoa. Pesticide resistance is also a problem in the long term.

There is a need to investigate the impact of M. tanajoa on other mite species including Tetranychus urticae and Oligonychus gossypii; also on cassava diseases including CMD and Cassava Brown Streak Disease Viruses. Research needs to be undertaken to establish the impact of M. tanajoa on biodiversity and Pest Surveillance to determine the current status of M. tanajoa.

Benin: IITA (Institut International d'Agriculture Tropicale), BP 08-0932 Cotonou, http://www.iita.org/

Kenya: International Centre for Insect Physiology and Ecology, P.O. Box 30772-00100, Nairobi, http://www.icipe.org/

Tanzania: Ministry of Agriculture, Food Security and Cooperatives, PO Box 2462, Dar es Salaam, http://www.agriculture.go.tz/

Tanzania: TanBIF, TanBIF, P.O. Box 4302, Ali Hassan Mwinyi Road, Kijitonyama (Sayansi ) COSTECH Building, Dar-es-Sala, http://www.tanbif.or.tz/

France: EPPO European and Mediterranean Organization, OEPP/EPPO, 1 rue Le Nôtre, 75016 Paris, France, http://www.eppo.org

Brazil: EMBRAPA, Embrapa Sede, Parque Estação Biológica - PqEB s/n°. Brasília, DF - Brasil - CEP 70770-901, http://www.embrapa.br/english

Colombia: CIAT International Centre for tropical Agriculture, Km 17, Recta Cali-Palmira, Apartado Aéreo 6713, Cali, http://ciat.cgiar.org/

26/08/2013 Updated by:

Beatrice Pollangyo, Ministry of Agriculture Food Security and Cooperatives, P.O.BOX 9071, Dar Es Salaam, Tanzania

03/11/1998 Orginal text by:

George Odour, CABI, ICRAF Complex, PO Box 633, Village Market, Nairobi, Kenya