COVER PHOTO: Larva of Erinnyis ello being preyed on by Polistes sp. CIA T i; a nonprofit organizutiuu de> ut<1d tu th,• agricultural and economic development of the iowland tropics. The Government of Columbia ¡>ru' id es support as hust country for CIA T and furnishes a 522· hectare farm near Cali for UA1\ h•·au4uartcr>. In addition. the Fundación para la Educación Superior (FES) makes available tu (.JA 1 the lll-4-hl'(tare substation uf Quilichao, situated near Santander de Quilichao, Departamento dd ( au(a. tullalwrati•·e work with the Instituto Colombiano Agropecuario (ICA) is carried out on se-eral uf it> c.,pcriutcntal stations a nd similar work is done with national agricultural agencies in othcr Lat111 Antcrican cuuntries. ('(A T is financcd h} a number of donors represented in the Con~ultati' e(, toup fur lntcrnational A¡:ricultural Research ( CGIA R ). During 1977 these donors were the Unitcd S t a tt ~ A~cll() for lntcrnational Development (\ ~A JO ), the Rockefeller Foundation, the Ford ~ oundaltvn. lhc \\'.h. Kellogj! f oundatinn, the Canadian lnternational Development Agenc} (CIDA¡. thc llltcrttatitJJIJI Uank fc;H Rcco_nstruction and Oevclopment (IBRD) through thc lnternational Ot,dupmcnt A»ucialiun (lif\ )/th_~ ~~~~American Ocvelopment Bank (IDB) and the governments of Au,tralta, lhl~ium . illl' l· cdcral Republic of Germany. Japan. the Nctherlands, Switurland and the Lnit~d Kut~d u n1. lu auuitiun, 'pccial project funds are ~upplied b y ,·arious of the aforementioned entitie~ plu> thc I11Lcruatiuual U e• dop,ncnl llesearch ( entre (! DR (') uf Ca nada and the United Nations Oevelopmcm Pru ~•antn,.·t l .'\UI'¡. This publication was financed b) th• (assa,·a lnformation Center al CIAT, a special pruject funlletl juintly by JDRC (Cassava Information P roject - Ph~• ll) and CL\ r's core budget. 1 7 Series 09EC-2 November, 197o CASSAV A PESTS AND THEIR CONTROL Anthony ,Bellotti Aart van Schoonhoven CCM~lJ Edited by BlBL \0 EC Trudy Brekelbaum 551l&c CASSAVA INFORMATION CENTER- CIAT Contents lntroduction 5 The host plant 6 Distribution of pests 6 Crop losses due to insects and mites 6 Mites and insects attacking foliage 9 Mi tes 9 Thrips 14 Cassava hornworm 17 Whiteflies 21 Leaf-cutter ants 22 G rasshoppers 25 Gall midges 26 Cassava lace bug 26 lnsects attacking stems 29 Stemborers 29 Fruit flies 33 Shoot flies 34 Scale insects 37 Mealybugs 41 lnsects that attack roots. cuttings and seedlings 45 Grubs 45 Cutworms 46 Termites 46 Crickets 49 Storage pests of dried cassava 49 Crop protection 50 The role of different control methods 53 The status of cassava entomological research 55 Literature cited 57 Appendix 1ndices for classifying pest damage 65 The cassava mite and insect complex 69 Cassava pests and their control* Anthony Bellotti Aart van Schoonhovenu 1ntr oduction Cassava ( Manihot esculenta). a major energy source for 300 to 500 million people, is grown throughout the tropical regions of thc world. lt is cultivated mainly in developing countries on small farms with little t cchnology. As a result. it has received limited attention from scientists and tcchnologists. FAO estimates for 1977 indicate an annual global production of 105 million tons on 11 million hectarcs. of which at lcast 55 mili ion are consumed by humans. Although cassava is now cultivated in sorne 90 countries. 80 pcrcent ofthc world's production comes from only 10; the six leading producers are Brazil (31%), Indonesia, Zaire, Nigeria, Thailand and 1ndia (98). 1n many parts of thc world, especially Wcst A frica, cassava appears to be the most economical. lowest risk subsistcnce crop for the small farmer. Thc increasing world population and the limited availability of energy has prompted a recent surge of interest in cassava, not only for traditional uses as a human food and for specialized starches including tapioca but also for animal feedstuffs and industrial uses (65). There is an cxcellent potcntial for increasing both yicld and arca under cultivation. Two international ccnlers for tropical agriculture. one in Colombia (Centro Internacional de Agricultura Tropical, CIAT) and another in Nigeria ( 1nternationall nstitute ofTropical Agriculture, liTA), carry out cxtcnsive research on cassava in addition to other tropical crops (98). Emphasis is placed on dcveloping high-yiclding germplasm for low-input conditions. Present world cassava yiclds undcr small-farm conditions average only 5 to 15 t f ha. Experimental yields of 55 t in Colombia (27) and 70 t/ ha elsewhere (97) ha ve been obtained. Commercial yields with low input in Colombia ha ve cxceeded 40 t / ha. Thcse figures indica te that undoubtedly there are severa! fa ctors limiting production undcr farm conditions, one of which is pests. 1t has frcquently becn reported that cassava is gencrally free of arthropod pests; however, prcsenl rescarch at C IAT and othcr centers rcveals that mite and insect damage does limit cassava production; e.g .. the recent introduction into A frica and the conscquent epidemic of the green mitc A1ononychellus tanaioa has caused serious crop losses (86, 104). Cassava pcsts represen! a wide range of arthropods: approximately 200 species have been rccorded. Although many are minor pests. causing little or no economic losses, severa! must be classified as major pests. These include mites. thrips, stemborers. hornworms. whiteflies and scale insects. Atmd~ed \cnwn appe:u(·d ongmally in lhc Annual Rc\itw of Fntomolog)' 23:39-67. 1978 1 ntornolog•:,t!ll. CIA f. Cah. Colomh1a 5 What little information is available on this subjecl- scattered in numerous journals and monographs- has been collected and made available to researchers through CIAT's Cassava lnformation Center. There is a paucity of data on cassava pest biology, ecology, dislribution, seasonal occurrence and economic damage, often resulting in confusion as lo iden1ifica1ion, laxonomic classification, delermination of synonyms and effective control measures. An attempl has been made to galher informalion on lhese pests with recent observation~ by th..: authors, whose experience has been mainly in Latín America. The host plant Manihot esculenta, a member ofthe Euphorbiaceae, is a perennial shrub that originated in the Americas; it was la ter taken to Africa and more recently introduced into Asia. Common names include mandioca, yuca, manioc and tapioca. Because of the different levels of cyanogenic glycosides it conlains in the roots, it has often been classified into "sweet" and "bitter" varieties. Leaves are formed at active apices and consist of an elongated petiole anda palma te leaf blade. The plant exhibits apical dominance, producing a single stcm; the petioles are borne on raised structures, giving the slem a characlerislic nobby appearance. When the main apex becomcs reproductive. apical dominance is broken; and two, three, or four axillary buds immediately below the reproductive slruclure become active and branching occurs. The roots accumulate carbohydrales in the parenchyma lo form swollen storage organs. Depending on ecological conditions, lhe planl is cultivaled from 8 to 24 months. Although the plant can be grown from seed, it is usually reproduced vegetatively for commercial purposes by planting stem cuttings. Cassava is grown commercially at altitudes between sea leve! and 2000 meters. Distribution of pests The greatest diversity of insects reported attacking cassava is from the Amcricas. Representatives of the 17 general groups of pests described in this review are f ound in the Americas, 12 are reported from A frica. and only 5 are from Asia. U ndoubtedly, pesl distribulion is more widely dispersed than the literalure indicates. Mites. whiteflies, whitegrubs. scales and termiles are reported from all major cassava-growing areas. The green mite Mononychellus tanajoa is reported only from the Americas and ccrtain parts of Africa ( 105). whereas the lwo-spotted spider mite Tetranychus urticae (T 1elariw) is reported worldwide. The white scale Aonidomytilus albus is reported from Asia. Africa and thc Americas whercas severa! other scale species are more localized. White grubs are reponed damaging cassava in severa! regions. but no single species appears universal. The cassava hornworm (Erinnyis ello), shoot flies, fruit flies, lace bugs (VatiKa manihotae) and gall midgcs are rcported only from the Americas. Stemborers. thrips. mealybugs and leaf-cutter ant~ are reported from the Amcricas and Africa. Grasshoppcrs are rcporled as a major pest only in Africa. Cutworms and crickets are found worldwidc but have nol been reponed as attacking cassava in all arcas. lt appcars that lhc pest complex varíes greatly overthe main cassava-growing arcas; therctorc. careful quaranline measures should be employed to preven! their introduction into uninte~tcd arcas. Crop losses due to insects and mites Insects can cause damagc to cassava by reducing photosynthetic arca. which results in} 1cld reductions: by attacking stems. which weakens the plant and inhibils nutricnt transpon: and by 6 MITES Oamage b) ¡\4onom ch t>llus tanaJoa (~ la nt un the righ t ) MITES ~r>rrt' allac~ h) .11. tonaioa attack i ng planting material. which reduces germination. Those mi tes and insects that attack the stcm a lso b sen the 4uantity and quality of planting material ta ken from these plants. thus affccting product ion. Soil-borne insects attack cuttings. causing wounds o r boring boles th ro ugh wh ich soil -borne pat hogens can en ter; thcy m ay al so complctely dest ro y t he epidermis and or hud ~ of the cuttings. Othcrs cut thc roots and 1or shoots shortly aftcr cmcrgcncc. Sorne insccts are vcctors of diseases as wcll. lndications are that pests such as miles. thrips. whitcflies,scalcs. mealybugs. lace bugs and ~ t c m horcrs. which attack the plant over a prolongcd period. will reduce yield more than those that dcfoliatc or damage plant parts for a brief period; e.g .. hornworms. fruit flies. shoot flies a nd lcaf-cuttcr ants.