I

THE SOURCES OF THE W-IXy4Sf,AN=1-9-SJj R. H. A. BAiGR 5, 1. 87 1. INTRODUCTION Baker et al (1986 & J.rr press) studied the in.rasion of sottth-eastern MaIi by savanna S. damnosum s.1. during the early rainy seasons of 1980 - 1985. After examining meteorological, hydrological, vector biting, morphologieal and .orrirol- inf ormation, they concluded that breeding sites in the Sankarani Basirr were not the principal sources of this invasion. These were to be found. instead on very large breeding s.ites further west on the Milo, Niandan, Kouya, Mafou and Niger. Eries from the sankarani Basin were, however, 'principally responsible for invasion at the most sor.rth-easterly point, Kank6Ia.

This short document reviews the same informatiorr for 1g8G to determine whether simllar conclusions can be made. Fig. 1 shows the rivers and capture points in the Upper Niger Basin irr Guinea arrd South-Eastern Mali with the source breeding sites believed to Lrave been principally responsibre for invasion in 1gB0-85. 2.

The 19BG control operations in the Sarrkararri Basirr were ri.ot, as in 1984 and 1985, designed specificalry to control invasion. Treatments were conducted principally to cl-ear the basin of all S. sanctipauli which might be re.sistant and could therefore transfer this resistance to S. sirbanum. One S. sanctipauli/sirbanurl hybrid was f ound on the R, Sankarani in Jtrne 1986 ULrC ilre viabiiiay o-f these hybrids is still- uncertain arrcl the ,sea::ch f or backcr.rss progeny continues.

From week 3 to week g the whole Sankarani Basirr was treated as part of the 9-LZ day treatment cycle. AbateR treatmerrt failures occurred on all ri-vers except the Dion, arrcl so these ri",ers were treated with Teknar from week 6. No treatments in the Sankarani Basin (except f or the Kourou-Kelle) r^rere conducted durirrg weeks 10-14, 22-24 or 40-SZ. From week lS to ZL (Znd week irr April to the 3rd week in May), the Gbanhala, Kourai, Dion bel-ow T6r:e arrd Sarrkarani were treated with TeknarR or TeknarRHPD but the Dion above T616 was left urrtreated. From week zs (mid-.]une) until week 39 (end of september), the whore of the sankarani Basin was treated with TeknarRHPD except for the main Dion (from Diamaraclou to the Sankarani) which was treated with permethrin. In week Z!, much of the Dion above T616 was subject to an insectieide treatment tr..ia1 which successfully interrupted breeding. The Fi6 was treated only from week 28 (2nd week of July) to r""k Sg with TeknarRHpD.

Prospections of the treated parts of the Sarr karani Basin revealed positive breeding sites,N, c)rr each occasion . On 24.4.86, pupae were found at Koimana ( 10o 11 go 3g,W) on the Sa (9040'N, nkarani and Gfte D Lebala 8o18'W) on the i(otrrai. On 23. 5, B 6, Iarvae and pupae were f ound at l(alaf ilia ( go 57,N, Bo O7,W ) arrd agai n at I(oimana orr the Sankarani. Treatments were suspended i n earLy Ju ne and prospections in week 24 (10-14.6.86) showed that onL y the Sarrk arani arrcl Di orr (which had not yet been treated) were s trongly po sitive. On 3. 7. 86, I(a1af ilia was again positive ( L++ p++ I and on 25. 7.86, 2 moriburrd Iarvae were found Aval Confluence Koura i ( Bo 27 '\1, 10o07'Vl) seven hours af ter treatnrent. . : ., , ,..8 ,l ' ar / - I ,/0 Overall in 1986, very few flies bred in the Sankarani Basirr except upstream of T616 on the Dlon. The treatment faiLures in the Sankarani River were probably due to the carry and dispersion of Teknar HPD. This is hard to check without more information on the dropping points and the quantities applied. The problem at KalafiIia is well known: the surface water at the beginning of the glte is subiect to a sideways current which passes through branches trailine from the left bank while the main river fLc,w (arrd the insecticide) passes straight through, avoiding these larvaI supports. Pilots have been requested to treat further upstream to ensure greater insecticide mixing.

3. METEOROLOGY & HYDROLOGY In 1986, the rains in south-eastern Mali were very good, exceeding the 1951-80 mean in ApriI, May, June and September at Bougouni (cf fig 2A). The annual total of 7127 mm was cLose to the 1951-80 mean of 1175 mm. At Kankan, records are incomplete but rainfa]l was close to the 1951-80 mean from April to JuIy but being badly deficient in September (cf fie 28). The ITCZ (fies 3A &.38) was equal to or further north than iri 1985 for the critical 14-23 calendar week period. Madina Diassa, the principaL morritoring point f or irrvasion, is at latitude 10o 50'N. The ITCZ remained to the north of this point from week 15, anci so the south-westerly winds for fly invasiorr should have been available from this time. Figs 4A,48 and 4C give the daily discharge,s of the Milo (at Kankan), the Niandan (at Baro) and the Niger (at Kouroussa) as received by satel-lite irr Niamey. Figs 5a, 58 ancl 5C show the mean weekly river heights since 1983 for ttre same rivers. The early part of the rainy season can be seerr to be rather sirnilar to 1985 for each river. In 1985 these Guinea rivers rose exceptionally late f rr-.,m extremely low leve1s, but this was equal-Ied or exceeded in 1986. Orr 22.5.86, the Niger at Diaragbela (near Kouroussa) and the Mafou at SSr6koroba were not flowing (though some flow was observed i-rr the Niger upstream of Earanah). Readings have been made at Kotrroussa since 1945 and although discharges at low water are imprecise, nc) previous record has been made of zero discharge. Eurther east in the Sankarani Basin, heavy April- rains in the Beyla area swelled the Dion and the few records which we have from the Sankarani at Mandiana (fig 23 confirms this early rise). n VECTOR POPIII,ATT ONS IN THE INVASTON ZONE OF'' SOI]TH_EASTERN MALI 4.7 Cvtotaxonomic Identif ications During 1986, several ]arval collectiorrs were iderrtified from the invasion zone of south-eastern MaIi. S. sanctipauli was common at I(ank61a (Kank6laba), Madina Diassa (Baoul6) and Metela (Bago6) in January. Eor the rest of the year, however, only S. sirLranum was identified (from Boundio-Bougouni (Baou]6) in May ancl September, Djigu6missala (Baou}6) in July and September, Nienambal6 (Ouassoulou-8a15) in June, Metela in May, Taouba (Baoul6) in Oct,ober, Fava (Faya) in August and Tienfala (Nieer) in August and October), except at the southernmost point, AvaI I'laclina (10o19'N, 7o46,W), where the Baoul6 crosses the frontier with Cdte cl'fvoire, Here 4 S. damnosum s.str. were identified with lg s. sirbanqn from a sample collected on 21.5.86. A sample f rom the san)e site colf ecteci on 19. 6. BG consisted of onl_y 29 S. sirbarrum. L-1

Thus, ds in previous years,. the principal invading species iri 19BG was S-__Ej:.be;1um which was joined by S. damnosum s.str. in the most southerly parts of this zone 4.2 Vector Bitirrs Populatiorrs Fis. 6A and 68 show the mean dairy bitine rates per week at Madina Diassa since 1979 for the 13-34 calendar week period (April to August). rt can be immediatel.y seen that 1986 was a year of very strong j"nvasion exceeding, &t its maximum, 1980. The maximum number of flies caught was 1058 on July 10th, giving a total for the 7 days of capture in week 28 of 5493, &n average of zB5 flies per day. The same picture was observed for Kank6l-a, Mpie1a and Faya, though at Mete1a, j-nvasion in 1979 and lgBO was stronger. Fie 7 plots the mean daily bitlne rates per week at all 5 sltes in south-eastern Mati during the 1986 invasion season. It can be seen that f1y numbers began to rise at l(ank61a and Madina Diassa irr week 20, in weeks 27-22 aL Metela and not until weeks 24-25 at Mpi6la and Eaya. At Kank6la and Maclina Dia.ssa, two peaks in f ly numberl were observed, the first between weeks 20-23 and a second Ionger and stronger wave between weeks 24-25 (26-27 at l(ank61a, Mpi6Ia, Metela and Faya) and 3L-32, peaking during week ZB. To what exterrt were these f lies invading? Invad.ing f lies are usually characterised by their high parous rate. We thus need to determine whether there were any instances of treatment failures or low parous rates. In week 20 at Madina Diassa only 27.8% of the 72 flies dissected (out of 209 captured) were parous. The Baou16 had only iust begun to flow, water temperatures were high and treatment frequerrcies and pilot instructions were not designecl to cope with this problem. However, by week 21, parous rates had climbea to 9B . 6%, suggesting a predominantly irrvasive population. At ltank6la, dtrring week 20,87.1% of the 31 flies dissected were parous, also suggesting a predominantly invasive population. The parous flies at Madina Diassa and Kank6la during week zo were hiehry infective (s.o% and 7.4% respectively, indicating an oId population. We thus have considerable evidence for concluding that this first peak in flies at Madina Diassa and Kank6la was only margirrally affected by loca1 breeding on the Baou16.

5. VECTOR POPULATIONS ]N THE SANI{ARANI & FIE BAS]NS Evaluating the efficacy of the Sankarani treatments and thus the potential r6le of the baslrr as a source of invaslon from vector collections has always been difficult due to the paucity of baseline data irr the Sarrkarani Basin. However, with 3 years of d.ata and frequent treatment suspensions, a picture of what vector populations would be preserrt without treatment is beginning to take shape. 5. 1 Cvtotaxonomic Identifications Recent iclentif ications have not greatly changed the clistribution of each vector species in the Sankarani Basin as described by Baker et al (1986), except for S. sanctipauli, whose redescription by post (1980) has lead to changes in its distribution with S. ioubrense. Identifications in this basin have been virtually .e"t.i"t"d to the dry season.

Table 1 shows that of the 56 larval collecttons ldentified fronr the Dion and arranged by month, none have been made between JuIy and September. Table 2 gives the identifications on the Dion arranged by ratitude, the records between the two thick lines being those 4

obtain.ed from the famous series of rapids upstream of Tere arrd downstream of the Sesseko confluence. Eor the Dion, therefore, it can be seen that the savanna species have a wide distribution, though they are probably rare in the south during the rainy season. Eew records are available for MaylJune, but it appears that the Dion above T616 is colonized principally by S. soubrense at this time and does not contain a huge breeding population of savanna flies. S. soubrense is virtuaLLy restricted to the raplds above T616, with the occasj.onal S. sanctipauli occurring there and further downstream towards the confluence with the Sankaranl. S. squamosum 1s rare irr the north but still occurs quite commonly ln the rapids above T616. Both S. sirbanum and S. damnosum s.str. have been found on the Sankarani, Iower Gbanhala and Iower Kourai, though the 1986 records irrdicate that S. damnosum s.str. was commoner i.rr January/February and S. sirbanum in May/June. S. soubrense was rare.r on these rivers than on the Dion while S. sanctipauli was found only on the Gbanhala and Sankarani between November 1985 and March 1986 and has not yet been recorded from the l(ourai. S. squamosum is common only in the. upPer stretches of these rivers. It breeds in the sma1l mountain headwater tributaries, many of which have never been treated. 5.2 Vector Bitins Populations Fies. B to 15 (A & B) portray the daily bitine rate per week at each capture point, whire MBRs are given in Tables 3 & 4 (recent MBRs, especialLy those f o.r December 1986 should be treated with car.rtion ) . Due to problems of accessibility captures in this area have never been regularr ancl so Lines drawn between points are there only to serve as a rough guide crf the weekly biting picture throughout the year. Vector biting rates were lowest at GbanhaLa on the lower Gbanhara, sasseidou on the upper Gbanhala, Sanankoro on the upper Sankararri and Diamaradou clrr the upper Dion. At Gbanhala, fly numbers dropped to near zero by the end (week 9) of the g-Lz treathent experiment, built up to over 100 per day during the 10-14 cafendar week interruption but remained very Iow from week l6 onwards suggesting successful treatments and 1ittle invasion from the Dion or from productive S. squamosum gttes upstream. EIy collections at Sasseldou were not frequent but showed that, ds usual, a small biting popuLation of S. squamosum remalned. Sanankoro was inaccesslble during August and September but the collections earlier in the year suggest that captures were affected for a much longer period (weeks 10-fE) by the ?-LZ treatment experiment. From weeks 17-25, the daily biting rates rose to remain generally between 15 and 50 with a high parous rate, suggesting invasion from the Dion. At Diamaradou, vector collections dropped after the 9-72 treatment experiment and did not recover untiL December. rt is possibre that vector coLLecti-ons are naturally low at this point during the Late dry and rainy seasons. The capture point at T616 is used to nronitor the efflcacy of treatments on the long and complex series of rapids upstream since it is generally believecl not to be much affected by invasiorr from other river basins. The 1985 treatments between weeks 16 and 35 (mid-April to end of August) dramt j.cally corrtrolled vector collections f rom weeks L7-4L. In 1986, fly numt,ers were low only between weeks 34 and 42.. The jrritial failure to reduce fly numbers at T616 with the permethrin treatments of the main Dion which started in week 25, was almost certainly due to not treating the tributaries, especially the Beni, until week 29. In 1985, the tributaries were treated much more corrsistently, with many prospections desigrred to check when each 5

started to flow. During the first part of the invasion numbers season, frv remai,ed at over 1s0 per d"y. The insecticide trial in week 27 had only, at most, a short term effect on fry numbers since in week 24 flies rapidly irrcreased. to over 400 a day. At Barauama, Mandiana Bac and i(ound.ianakoura, wele high biting l-e.reIs recorded for onl-y a short periocl in the middre oi the y*Ir, u period coinciding witir the invasion in south-eastern MaIi (thoush at Baranama, f lies were also conrrnon at the.beginning of the year).- At Koundianakoura, the records are inadequate to indicate when the flies first became ntunerous, but they reachJd a peak in week ZB (the same week as the peak at Mad.ina Diassa and Kankela). At Mandiana , tti numbers rose sharply in week 24, reached a peak in week 26 but no captures were made in week zg. At Baranama, increased fry captures arso sharpl-y in week 24, increasi.ng erratically to a maximum of 190 flies per day in week 31. t) 6.1 Vector collections during 1986 confirmed the picture obtained in previous years. S' damnosum s.str. was absent from trre other in the Upper Niger Basin west rivers populations of the Sankaranl. Enormous breecling of S' sirbanum in company with S. were to be found on the Milo, the Niindan, the ito*y., thJ "o,rUr.rr=.Mafo,, and the rn week 2L (22'5'86), rarvar supports, Niger. were tlack with rarvae and pupae found on the Milo at Bafe1e (10o01,N) and on the Niandan at Bessekoro (9o31'N). These rarvae were alt id.entified as rn the same week-, the s. sirbanum. flowing. Kouya, Mafou, Niger and Fi6 were stirl not In week 27, similar heavy U"E"aing was discovered on the Milo at Baf€le, the Niandan (lt the Rapides (goSS,N) and Bessekoro), the Kouya, the upper Mafou and the Nielr below Balandougou (10o46,W). In the salne week, the lower Mafou was-not flowing and the Rapicles ciu Niger ( 10o 0 7 'W ) had only .iust started to f low. 6.2 Vector Bitine populatiorrg

Fie=. 16 to 19 (A & B) portray the daily bitine rate per week at Morigbedougou and L6re on irre Miio, Diaragb6la Sansant"y. Niandan and on the Niger. Lele is upstream-Fit of the ""-trr"Chutes Milo where S. soubrense is principatly found numbers exceeded 50 per at this point rarely dav so it is unlikely trr"t the Chutes Milo played a bie r6le in the 1986 invasion. on tire other hand at Morigbedougou, sansanbaya and Diaragb6la, savanna fIy captures rose to great heights during the i.nvasion season with . ,.*i*,r, of gg3 week 24' At Morigbedougou, at sansanbaya. in ffy numbers ?rere greater than 1oO per day throughout but.ro?e sharpry between ,..k= 16 between 300 and ina 19. Two peaks 400 flies per day were observed in weeks 19 and 26 and flv numbers ferl in weeks 30-33. At sansanbiya,-the flies started to increase sharply in weeks ZO-Z!, reachld thelr peak in week 24 and fell steeplv in week 28. l"ater, starting At Diaraebela , f]y numbers rose in week 24, rising rapidry i" w"ei 22, reaching a peak in week 28 and falling in weeks SS-SS. 7. DISCUSSION Baker et al (in press) provided the suspected fotlowing criteria which source breeding sites should satisfy before they can be implicated in the invasion of south-easterrr. Mari: ( 1 ) Since the principal invading species is S. sirbanum, the source rapids should be of suf f icient slze to prociuce very €i

large numbers of this sPecies (2) FIies caught at source should be in the same size range as those caught on arrival in the invasion areas. (3) Sirrce invading f lies are rnoved f rom their breeding sites with the assistance of the south-westerly monsoon winds, these breedirrg sites nrust lie up*wirrd and to the south-west of the invasion zone. (4) These Long distance nrigrations are known to occur during the early to middle wet season (ApriI-May to August-September) bqt the processes which initiate, orientate, terminate and determine their strength are poorly understood. The time scale suggests that they start when the Irrter-Troplcal Convergence Zone (ITCZ) passes north of the source breeding sites providing the south-westerly winds needed for fly movement and occur at times when the rivers are beginning to rise after the first rains have fallen, increasing the productivity of the breeding sites. The end of the migration occurs when the south-westerly winds are stitl hlowing ancl may thus be due to the flooding of these breeding sites. We might, therefore, expect a relationship between the movement of the ITCZ, the water leveLs in the source rivers and the periodicity of invasion. T[e rapids in the Niger, Mafou, Kouya, Niandan and Mi]o were shown to satisfy aII these criteria on the evidence obtainable in 1985. For 1986, the same criteria need to reappraised. 7.L S. sirbanum Breedine Sites As in previous years, enormous productive breeding sites of S. sirbanum were found on the Lower MiIo, Iower Nlandan, Kouya, Mafou and Niger. The Sankarani. was f ound to contain both S. damrrosum s. str. and S. sirbanum breeding sites. In 1986, the main savanna breeding sites on the Sankarani, Kourai, Gbanhala and Dion below T616 Yiere controlled for most of the invasion season. AII larvae identified at points where treatment failures had occurred ( see page I ) were identified as S. sirbanum. Treatments were interrupted in weeks 22-24, but this was not Long enough to allow signlficant vector breeding. The treatments of the Dion above T616 in week 2l and from week 25 - 40 only sIowly brought bitine rates dowrr because the tributaries were not treated until week 29. The Dion above T616 was thus a potentiaL source c-,f the f lies invading MaIi during the early part of the invasion season. The few cytotaxonomic identifications made from this famous stretch of the Dion during May and June indicate, however, that S. soubrense and not saYanna species are dominant tftere cluring this perlod. However, the presence of S. damnosr.rm s.str. at Madina on the Baoul6 near the Cdte d'I.roire border in May, sr.rggests strongly that f Iies from the Sankarani Basin rnust corrtribute to j.rrvasion sirrce no breeding sites of this specles occur further west. 5.2 F1v Size This wil.l be the subiect of a separate report by M. Wi Isorr. Once again, however, flies in the potential source areas of the Sankarani and Upper Niger Basins were shown to be within the same size range as those caught in south-eastern MaIi. 5. 3 Winds Wind direction data for 1986 have not been available for analysis but there are no reasons to doubt that the for previous years also hold true same conclusions s.+ The movement of the pubrications ITCZ has already been shown ln previous not to be a vgry good guid.e to the perlodiclty of invasion. once again in 19g6, the capture points ricz had moved north of the in the invasion zone, well before the invasion started invasion had stopped rong before the rrcz had moved s6qrrr.:3:.:n" south As before we must water conrpare the periodicity of invasion with the levels in the potentiar sourc3.i,r."" which have been affect the productivitv of tire ureeJr"e sites. shown to biting rates along rn 19g6, the vector productivity. the source rivers piovided an .*ir. indication of Fie=. Z0 & 21. show the daily biting rates per Diassa and the principal capture points week at Madina source areas in the potential_ invasion in Guirrea during the invasj.on Eigure zz pr_ots the dailv bitlne rate per week at Madina Diassa=..=Lrr. levels (in metres) of the principal against the river To rivers in the upper Nlger Basin. show the changes in river revers more crearly, these have plotted on their owrr in fie. 23. been Niger are The records for the sankarani and incomprete. Both the r""ora= for the Niger at Earanah at l(ouroussa have been protted because and invasion season. together they cover the

The invasion of south-eastern Mali at Madlna Metela started in weeks Diassa, Kank6la and flies 20-27. ttrese-ities wourd [. tr,. progeny of laying eggs in weeks 18-20 and one would expect that rivers wourd have iust risen and vector the source river banks would colrections arong the source also have begurr to ,i."" sharply durlng weeks (assuming invading flies bite Uefo.e ifr.y travel). lg_Zl The sankarani rose sharply in week Niandan in weeks 19-20 ("itt.polated 16, the M110 in week 77 , the Niger (at Fararrah) trom i-ncomprete recogds) and the in weeks z1-zz. goih tr,e s"nrra"anl and Milo (and to a lesser extent the Niandan) are th;; candidates the first wave of invasion. ior the source of Daily bitine rates at T616 in the Sankarani Basin (Dion) Morigbedougou on the Mi.lo were between ancl period, though the zoo and 3oo during this Morigbeclougou had risen sharply (by three times since week 16) wrrrte th; T616""i"fl"= peak coLlections at T616 "ui"rr"= had harved. vector arrd Morj-gbeclougo,, **r* made in weeks zs-26. corrections at sansanbaya ii." Niandan rapicilv irr weeks zo-21 (maxin,r* "" -ia) began to increase Niger *..t and at Diaragbela on the in weeks 26-27 (maximum week zB). The c.ul6l thus have come first invading fries either from th; oion or the Mi1o. However, since Lriting rates were sharply inc.eisir* o, were fallirrg on. th9 Dion, the Milo while they this th; L*t"rri-to-wrrrch the Dlon above T616 at season is hiehry prod.r-rctive for s. sirbanum is g.eat increase in f fy uncrear, and no (as numbers was uE-E-.a.r.ru, downstream of T6re would be expected if the Di;;-flies"i=Er.r"o had just more mobile), the Milo is a stronger become much first invading flies. cancjidate .u-it. source of the The fal] in vector dramatic irrvasi.on during weeks 23'24 and the rise during week 25 can be explained by the fall in fly 8 numbers on the Dion and Mito (even arrd-the rapid increase at arr points Mandiana Bac orr the lower santarini which is far from large breeding sites) during week 24. r},u increased during lli"ndan popur.iior, rapidry the weeks zo-24 u"a ,"=t also have played a major role in the second wave of invasion. most northwestwards points This second wave reached the of F.ya and Mpi6la .f=o in week 24 but f Iv numbers did rrot ir,.r.au. rapidly until weeks because these points .r.-tnvaaeh p.LOoniinantly Z1lia, possibly Llpper Niger itself by flies from the The magnitude of the 1gg6 invasion, whlch exceeded that observed in the 1979-1gBS period, was most probably due to the source rlver leve]s staying low for a very ]ong time. This allowed vector breeding to take place before extensi.ve flooded. these Ureeaine =it.= were The 1986 invasion ended irr weeks 31_34, a time of rapidly rising rj-ver Ievels in the source rivers and fatline L'lpper Niger Uiiing rates in the Basin. As in previous years, the Niger was the last reach a river level of 2 n (in week -"rra to the invasion. 35) this presaged the end of C

6. SUMMARY & CONCLUSIONS 6 ' 1 The 19BG invasi-on of south-eastern Mali was stronger tharr in any of the previous seven years in which this phenomenon has been studied. s. sirbanum was again shown to te the main invading species with small populations of S. damnosum s.str. at the southernmost points . For the f irst tirn;, bit'1"g rates in both source and invaded areas courd be compared. 6'2 Despite erratj.c treatments in the Sankarani Basin, very little breeding occurred except on the Dlon upstream of T616 which was not properLy treated until the heisht of the invaslon in Mali. 6.3 Some LocaL breeding in south-eastern MaIi and. in treated stretches of the Sankarani Basin was not thought to have had an important effect on vector biting rates. 6.4 It was concluded that the Dion important upstream of 1616 was less than the Milo as a =oui"e of the first wave of flies which invaded Mali in mict-May since bltlng rates at T616 were decreasing at the time, rro concomitant rise was observed at Baranama downstream ancl cytotaxonomic identifications iirAicat"a that this stretch of river is principally colonized by S' soubrense at this time of the year. At Morigbedougou on the Milo, however, fry numbers had srlatry increased and rarvar supports were blaci< with larvae and pupae of S. slrbanum during the same period. The Milo had started to rise from its annuaL low 3 weeks before, and. the Sankarani 4 weeks before the bitlng rate in l"Iali began to rise. 6'5 Vectors from t}1e Sankararri Basin,rnust have contributed to the invasion since s. damnosum s.str., which onry breeds in this basin in Guirrea, was recorcled f rom the Baour6 on the c6te d'Ivoire border with Mali. It is probable that flies from the Sankarani Basin prirrcipally invaded the area to the extreme south and east of Mali and the extreme cot* ";;;h "i d,Ivoire. 6,6 The heieht of the invasion in early July water le.,zels coincided with rising arrd bitine rates throughout the Urn." Niger Basin but especiarlv on the Niandan and Nrger. rrr"-frie"" (and was the rast river to rise Mafou) rerationshlp and there appeared to be a between the.lerrel of thls river-l,tprer. and the start of invasion at the most northeasteriy points, and Faya. 6'7 The end of invasion coincided wlth rapidly rislng and flooding water fevels throughout the Upper Nleer Basin ir, earLy August. 6'B Erie's from both source and invaded areas r^rere size range. within the same 6.9 The importarrce of breecllng as ^!,h* sltes 1n the Upper Niger Easln the source of flies invading south-eastern Mali was again confirmed. Proof should come when these breeding treated this year sltes are