Colour variation of the head bug (Eurystylus oldi) in relation to Sorghum bicolor panicle or grain colour is reported. Results of different feeding experiments of E. oldi on sorghum of different colours are reported. Data from these research showed that the colour of the head bug changed with the colour of the food they consume. However, a few exceptions are noted, and these may be due to the changes in grain pigmentation during development that may not be apparent in the immature grain fed to the nymphs. These observations suggest that the different species of head bugs on sorghum may be colour morphs of the same species

Ratnadass, A

Sharma, H C

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Colour variation in the African sorghum head bug

Sifuentes, J.A., Mughogho, L.K., and Thakur, R.P. 1992.Inheritance of resistance to sorghum leaf blight. Pages 16-17 inCereals Program Annual Report. Patancheru 502 324, AndhraPradesh, India: International Crops Research Institute for theSemi-Arid Tropics. (Limited distribution)Tarumoto, I., Isawa, K., and Watanbe, K. 1977. Inheritance ofresistance in sorghum-Sudangrass and sorghum hybrids. JapanJournal of Plant Breeding 27: 216-222.Widstrom, N.W., Wiseman, B.R., and McMillian, W.W. 1984.Patterns of resistance to sorghum midge. Crop Science 24: 791-793.Color Variation in the African SorghumHead BugH C Sharma1 and A Ratnadass2 (1. InternationalCrops Research Institute for the Semi-Arid Tropics(ICRISAT), Patancheru 502 324, Andhra Pradesh,India. 2. ICRISAT-Centre de cooperation inter-nationale en recherche agronomique pour ledevelopment (CIRAD), BP 320, Bamako, Mali)Sorghum [Sorghum bicolor (L.) Moench] is an importantcereal crop in West Africa. It is damaged by over 150species of insects worldwide, of which Eurystylus oldi Poppius (Heteroptera: Miridae) is one of the mostdamaging pests in West and Central Africa (Ratnadass etal. 1994). Published reports of Eurystylus spp. on sorghumsuggest a complex of species are involved in West Africa.Eurystylus marginatus Odh. was recorded as the dominantspecies in Mali (Doumbia and Bonzi 1985),E. rufocunealis Poppius in Nigeria (MacFarlane 1989),E. risbeci Sch. in Senegal (Risbec 1950), E. marginatus inNiger (Steck et al. 1989), and E. immaculatus Odh. inNigeria and Mali (Sharma et al. 1992, 1994; Ratnadass etal. 1994). However, based on head bug collections fromseveral locations in West Africa, Stonedahl (1995)reported that the major head bug species infestingsorghum in West Africa is E. oldi Poppius, withE. bellevoyei Reuter sometimes occurring as a minor pest.Previous identifications of E. marginatus weremisidentifications, while E. risbeci and E. immaculatus are synonyms of E. oldi. This confusion about speciesidentity has, to an extent, been due to various color morphsof E. oldi, and to different names being assigned bytaxonomists at different times/locations.Few farmers recognize head bugs on sorghum, and mostare not familiar with the nature of the damage these insectscause. Agronomists and breeders in general are unaware ofhead bugs, and their damage potential. This ignorance isattributable to the relatively small size of the insects, andthe fact that both nymphs and adults tend to assume thesame color as that of the panicle/grain. There is therefore a need to educate farmers/extension workers, agronomists,and breeders on the identification and pest status of E. oldi in West and Central Africa. In this paper color variation inE. oldi in relation to panicle/grain color in sorghum isreported.In 1989, first- and second-instar head bug nymphscollected from sorghum panicles in the field in Nigeria andMali, were sorted into red, red-brown, and green colormorphs. The nymphs were reared on green or red-coloredsorghum grain, corresponding to 'white' and 'brown' grainclasses. Red-colored nymphs reared on red graindeveloped into reddish adults with bluish-greenundersides, while the green nymphs reared on green graindeveloped into greenish-brown adults with bluish-greenundersides. Red-brown nymphs reared on green grainbecame brown-black adults, with light green undersides.Red nymphs reared on green grain became light green orred, while green nymphs reared on red grain developedinto light green adults. Dark brown nymphs reared ongreen grain became brown-red adults.Observations on the changes in color of the nymphs andadults were confirmed during the 1999 rainy season atSamanko, Mali. The green first-instar nymphs collectedfrom white- or tan-grained sorghum cultivars S 34 orICSV 197, that have green immature grain, developed intogreenish-brown adults with bluish-green undersides whenreared on the maturing green grains of the same white- ortan-grained cultivars, or of chalky-grained cv Nagawhite.The green first-instar nymphs collected from white- or tan-grained sorghum cultivars, S 34 or ICSV 197, developedinto reddish-brown adults with bluish-green undersideswith distinct red markings on their abdominal segments,when reared on the maturing red grains of Sorvato 28 orFramida (which is actually brown-grained: its grain hasboth a pigmented testa and a red pericarp).The green third-instar nymphs collected from paniclesof the tan-grained sorghum cultivar ICSH 89002developed into greenish-brown adults with bluish-greenundersides when reared on the maturing green grains ofthe same tan-grained cultivar. However, the nymphsdeveloped into light green adults when reared on thematuring red-brown grains of Framida. The red third-instar nymphs collected from panicles of the red-browngrained sorghum Framida developed into reddish-brownadults with light green undersides in males, and bluish-green females with red markings on their abdominalsegments, when reared either on the maturing red grains of42 ISMN 41,2000the same cultivar, or on maturing green grains of tan-grained ICSH 89002.Thus, the color of the head bugs changed with the colorof the food they consumed. However, there were a fewexceptions, that might be due to changes in grainpigmentation during development, that might not beapparent in the immature grain fed to the nymphs. Theseobservations suggested that the different species reportedearlier on sorghum are in fact the color morphs of the samespecies, as confirmed by the taxonomic studies ofStonedahl(1995).ReferencesDoumbia, Y.O. and Bonzi, S.M. 1985. Note sur les problemesdes insectes des panicules du sorgho au Mali. Pages 173-182 inProceedings of the West African Regional Sorghum NetworkWorkshop. 21-24 Oct 1985, Bamako, Mali. Ouagadougou,Burkina Faso: Semi-Arid Food Grain Research andDevelopment/International Crops Research Institute for theSemi-Arid Tropics.MacFarlane, J.H. 1989. The hemipterous insects and spiders ofsorghum in northern Nigeria. Insect Science and its Application10: 277-284.Ratnadass, A., Cisse, B., and Malle, K. 1994. Notes on thebiology and immature stages of sorghum head bugs Eurystylus immaculatus and Creontiades pallidas (Heteroptera: Miridae).Bulletin of Entomological Research 84: 383-388.Risbec, J. 1950. (I). La faune entomologique des cultures auSenegal et au Soudan Francais. Dakar. Senegal: GouvernementGeneral de I'Afrique Occidentale Francaise, 498 pp.Sharma, H.C., Doumbia, Y.O., and Diorisso, N.Y. 1992. A headcage technique to screen for resistance to head bug.Eurysrylus immaculatus Odh. in West Africa. Insect Science andits Application 13: 417-427.Sharma, H.C., Doumbia, Y.O., Scheuring, J.F., Ramaiah,K.V., Beninati, N.F., and Haidara, M. 1994. Genotypicresistance and mechanisms of resistance to the sorghum headbug, Eurystylus immaculatus Odh. in West Africa. Insect Scienceand its Application 15:39-48.Steck, G.J., Teetes, G.L., and Maiga, S.D. 1989. Speciescomposition and injury to sorghum by panicle feeding bugs inNiger. Insect Science and its Application 10: 199-217.Stonedahl, G.M. 1995. Taxonomy of African Eurystylus (Heteroptera: Miridae), with a review of their status as pests ofsorghum. Bulletin of Entomological Research 85: 135-156.Predation by Cheilomenes propinqua on Corn Leaf AphidI O Dicko (Institut du developpement rural, Univer-site de Ouagadougou, 03 BP 7021 Ouagadougou-03,Burkina Faso)IntroductionThe corn leaf aphid, Rhopalosiphum maidis Fitch(Homoptera: Aphididae), is among the insect pests ofsorghum [Sorghum bicolor (L.) Moench] that causeeconomically important damage to the crop (Teetes et al.1983). Direct damage, observed during attacks by largecolonies of R. maidis on young sorghum plants, can killseedlings. Indirect damage includes both secretion of a honeydew that favors the development of molds, andtransmission of such viruses as the sorghum dwarf mosaicvirus (SDMV) (Hagen and van den Bosh 1968).Extensive use of broad-spectrum chemical pesticides,usually prescribed to minimize insect pest damage onsorghum, is rarely cost effective and often leads to thedevelopment of resistance within populations of R. maidis (Young and Teetes 1977). Hence, there is an urgent needthat alternative control methods to chemicals be developedand made available to farmers.Cheilomenes propinqua Mulsant (Coleoptera:Coccinellidae) is a polyphagous predator widelydistributed in Africa (IIE 1996). It is a potential biologicalcontrol agent for R. maidis. However, attempts to includeC. propinqua in a biological control program require (asfor any other predator) that adequately designed studiesgather detail information on its vital functions, includingits numerical and functional responses. Holling (1963)defined the functional response of a predator as its abilityto linearly increase its consumption in response toincreasing population densities of the prey. Thus, thepredation effectiveness, or voracity of a predator, is a keycomponent of its functional response.This paper summarizes results on laboratory evaluationof the predation effectiveness of C. propinqua adults andlarvae on R. maidis. Materials and methodsIn 1997 and 1998 C. propinqua and R. maidis werecollected from field-grown sorghum plants at theUniversity of Ouagadougou's Research Station, located 20km from Ouagadougou, Burkina Faso.Aphid prey were captured by excising sorghum leaveson which they had formed large colonies. Excised leafpieces were then carefully placed in 1.5-L, covered.ISMN 41,2000 43

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Colour variation in the African sorghum head bug

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