Arthropod Pests
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Color profile: Disabled Composite Default screen Chapter 11 Arthropod Pests Anthony C. Bellotti Pest and Disease Management Project, Centro Internacional de Agricultura Tropical (CIAT), A.A. 6713, Cali, Colombia Introduction especially if there is a dry season of 3 months or more. When the crop is grown under conditions The dynamics of cassava production, utilization of irregular, limited rainfall as in the lowland sub- and marketing vary considerably from one humid and semiarid tropics, however, arthropod continent and country to another. In recent pest populations increase, causing considerable years there has been a shift in demand for partic- yield reduction (Bellotti et al., 1999). Arthropod ular cassava products in Latin America with a pests can cause low-to-moderate levels of crop noticeable trend towards the production of chips damage in the subtropical regions of Latin and pellets for animal feed, as well as high- America and Africa and in the highland regions quality flours for human consumption (Henry of Africa (Henry and Gottret, 1995). and Gottret, 1995). This could induce a trend Most cassava is grown by small-scale towards plantation-size production units. farmers, often on marginal or fragile soils under World cassava production, which is con- rainfed conditions, using few purchased inputs centrated in Latin America, Asia and Africa, such as fertilizers or pesticides. In these tradi- can be divided into five principal agroecosystems tional farming systems where cassava is usually (Henry and Gottret, 1995): one of many crops being grown, pest control • is often a low priority and so cassava receives the lowland humid tropics; minimal pesticide applications. Under such • the lowland subhumid tropics; • conditions, yields are often low, with a large gap the lowland semiarid tropics; between potential yield (21.3 t ha−1) and that • the highland tropics; and −1 • achieved by producers: a mean of 11.2 t ha in the subtropics. Latin America and 9.0 in Africa (Henry, 1995). Approximately 65% of the area under Arthropod pests and diseases are major factors in cassava production occurs in the lowland humid causing this yield reduction (Bellotti et al., 1999); and subhumid agroecosystems (Henry and moreover, the vegetative nature of cassava prop- Gottret, 1995). Arthropod pests do not appear to agation contributes to pest build-up and dissemi- cause significant damage in the lowland humid nation across regions and among countries and or the highland tropical agroecosystems, where continents. there is considerable and consistent rainfall In Latin America there are indications of a (Montagnini and Jordan, 1983; Bellotti et al., shift towards large-scale production units, where 1999). Moderate levels of crop damage can occur cassava is grown as a plantation crop. This may in the mid-altitude (1000–1400 m) tropics, result in new or worse pest problems than those ©CAB International 2002. Cassava: Biology, Production and Utilization (eds R.J. Hillocks, J.M. Thresh and A.C. Bellotti) 209 221 Z:\Customer\CABI\A4101 - Hillocks - Cassava\A4212 - Hillocks - Cassava #R.vp Monday, February 04, 2002 11:22:58 AM Color profile: Disabled Composite Default screen 210 A.C. Bellotti found in small-scale production. Such a scenario established and native arthropod pests that have is especially feasible in the Neotropics, where a adapted to cassava have not been reported as large complex of arthropod pests has co-evolved causing serious yield losses (Maddison, 1979). with the crop. For example, increased frequency Recent explorations in cassava-growing and severity of cassava hornworm (Erinnyis ello regions of the Neotropics indicate that the L.) attacks have been recorded, resulting in arthropod pest complex is not geographically increased pesticide applications (LaBerry, 1997). uniform. The evidence suggests that the mealy- In Asia, where there are extensive areas planted bug Phenacoccus herreni, which has caused with cassava, major pest problems have been considerable damage in northeast Brazil, was avoided as the most damaging pest species from probably introduced from northern South Amer- the Neotropics have not been introduced. ica (Venezuela or Colombia), where mealybug populations are controlled by natural enemies not found in Brazil (Bellotti et al., 1994; Smith The Cassava Arthropod Complex and Bellotti, 1996). P. manihoti, which has caused severe crop damage in Africa, occurs only Cassava (Euphorbiaceae: Manihot esculenta in Paraguay, the Mato Grosso area of Brazil and Crantz) is a perennial shrub grown commer- the Santa Cruz area of Bolivia (Lohr and Varela, cially as an annual or biennial, throughout 1990). tropical and subtropical regions of the world. Studies on the CGM demonstrate a higher This vegetatively propagated crop has a long degree of morphological polymorphism and a growth cycle and is drought-tolerant. As it greater Mononychellus species complex in is often intercropped and planting dates are northern South America than elsewhere in the staggered, cassava is almost always present in Neotropics (Bellotti et al., 1994). This diversity is farmers’ fields. These agronomic characteristics associated with greater species richness within undoubtedly contribute to the considerable the phytoseiid complex that preys upon Mono- diversity of arthropod pests that feed on the crop. nychellus spp. in cassava (Bellotti et al., 1987, Cassava originated in the Neotropics, 1999). The cassava pest complex can be divided although its exact centre of origin is equivocal into two groups: (Renvoize, 1973; Allem, 1994; see Chapter 4); • those that appear to have co-evolved with consequently, the greatest diversity of arthro- cassava, which is their primary or only pods reported attacking the crop (Table 11.1) host; and is from the region (Bellotti et al., 1994). An • generalist feeders that may attack the cas- estimated 200 species have been reported sava crop opportunistically, especially dur- (Bellotti and Van Schoonhoven, 1978a,b), many ing seasonally dry periods when cassava is of which are specific to cassava and have adapted one of the limited food sources available. in varying degrees to an array of natural biochemical defences in the host that include The former group includes the Monony- laticifers and cyanogenic compounds (Bellotti chellus mite complex, mealybugs (P. herreni and and Riis, 1994). The pest complex varies greatly P. manihoti), the hornworm (E. ello), lacebugs between the main cassava-growing areas, (Vatiga illudens, Vatiga manihotae, Amblystira indicating that careful quarantine measures machalana), whiteflies (Aleurotrachelus socialis could prevent pest introduction into uninfested and Aleurothrixus aepim), the stemborer (Chilo- areas (Frison and Feliu, 1991). The accidental mima clarkei and those of the genus Coelosternus), introduction of the cassava green mite (CGM; fruitflies (Anastrepha pickeli and Anastrepha Mononychellus tanajoa Bonder) and the cassava manihoti), the shootfly (Neosilba perezi), the white mealybug (Phenacoccus manihoti Mat. Ferr.) from scale (Aonidomytilus albus), thrips (Frankliniella the Americas into Africa has caused considerable williamsi) and the gallmidge (Jatrophobia brasil- crop loss throughout the cassava belt and has iensis; Bellotti et al., 1999). been the object of massive biological control The generalist feeders primarily consist efforts (Herren and Neuenschwander, 1991; of whitegrubs (Phyllophaga spp. and several Neuenschwander, 1994a). In Asia none of the others), termites, cutworms, grasshoppers, leaf- major neotropical cassava pests has become cutting ants, burrower bugs (Cyrtomenus bergi), 222 Z:\Customer\CABI\A4101 - Hillocks - Cassava\A4212 - Hillocks - Cassava #R.vp Monday, February 04, 2002 11:22:59 AM Color profile: Disabled Composite Default screen Arthropod Pests 211 crickets, Tetranychus mite species and stemborers become a major pest if introduced into areas (Lagochirus spp.) (Bellotti and van Schoonhoven, where native natural enemies and/or adapted or 1978a; Bellotti et al., 1999). resistant germplasm are unavailable. P. manihoti Several pests found in the Neotropics could has not yet reached other regions, although potentially cause severe crop losses if introduced there are no evident natural barriers to prevent inadvertently into Asian or African cassava- its movement, especially in Brazil, where cassava growing areas. They include the cassava horn- is grown extensively throughout most of the worm, several mite species, lacebugs, whiteflies country. The Andean mountain range in west- and stemborers. Moreover, a species which is ern South America has undoubtedly affected the considered to be a secondary or minor pest in the movement of cassava pests, although this is not Neotropics (e.g. the cassava mealybug, which is well documented. For example, the lepidopteran found only in limited sites, as mentioned) could stemborer C. clarkei, which has good flight Table 11.1. Global distribution of important arthropod pests of cassava. Pest Major species Americas Africa Asia Mites Mononychellus tanajoa X X Tetranychus urticae X X Mealybugs Phenacoccus manihoti X X Phenacoccus herreni X Whiteflies Aleurotrachelus socialis X Aleurodicus dispersus X X X Aleurothrixus aepim X Bemisia tabaci X X X Bemisia afer X X Hornworm Erinnyis ello X Erinnyis alope X Lacebugs Vatiga illudens X Vatiga manihotae X Burrower bugs Cyrtomenus bergi X Thrips Frankliniella williamsi X X Scirtothrips manihoti X Scales Aonidomytilus albus X X X Fruitflies Anastrepha pickeli X Anastrepha manihoti