Although chemical control methods have been used in anti-tsetse campaigns in 18 countries in Africa, side-effects on non-target organisms have only been studied in five of these, viz. Botswana, Kenya, Nigeria, Uganda and Zambia. These studies are listed in Table 3.1 In this chapter a general account will be given of the studies referred to in the table.
Table 3.1. Studies on side-effects of the chemical control of tsetse files considered in the present report
|Country||Year (s)||Type of insecticide + method of application||Reference|
|Dieldrin groundspray (mistblower)|
Endosulfan ULV fixed-wing
Russell-Smith (unpublished report, 1976)
Russell-Smith (COPR, personal communication)
|Koeman and Pennings (1970)|
Koeman et al. (1969)
Alsop (personal communication)
Dieldrin ULV helicopter
Dieldrin/endosulfan ULV helicopter
Endosulfan ULV fixed-wing
|Koeman and Pennings (1970)|
Koeman et al. (1971)
Koeman et al. (1976)
Takken et al. (1976)
|Serunjoji and Tjell (1971)|
|Dieldrin groundspray (mist-blower)|
Endosulfan ULV fixed-wing
Magadza (unpublished report, 1969)
Botswana appears to be the first country in Africa where side-effect studies in relation to chemical control of tsetse have been carried out. In 1964 riverine forests were sprayed against G. morsitans in an area near Maun. The pesticide used was dieldrin which was applied by both Unimag and knapsack spraying equipment. The effects on non-target organisms were observed for a period of 10 days following spraying. Among the animals found dead were many birds, mammals, reptiles and fish (Graham, 1964).
The other studies carried out in Botswana all concern the ULV fixed-wing applications of endosulfan which were started in 1975. The spraying is carried out in the Okavango Delta where savanna areas around the swamps are repeatedly (4–5 applications) sprayed at a dose rate of 6 g endosulfan a.i. per hectare. Special attention was paid on possible effects on the aquatic ecosystem. The preliminary results which have come available so far show that no measurable effects occur in fish and aquatic and terrestrial invertebrates (Russell-Smith, 1976).
In this country studies were made in 1968. This concerned dieldrin groundspray applications against G. fuscipes and G. pallidipes along the shores of Lake Victoria and the riverine forest on the slopes of the Ruri hills (Province South Nyanza). It was found that in particular insectivorous birds and many species of non-target insects died in fair numbers due to dieldrin poisoning. In table 3.2. residue levels found in livers and brain of some of the victims, are listed. Analyses were also made of rodents, birds and fish collected in the areas sprayed. The dieldrin levels in the livers of 18 out of 20 small rodents (Arvicanthis niloticus, Lemniscomys striatus, Mastomys natalensis and Aethomys kaiseri) varied from 0.01 to 0.52 ppm. Only in two specimens the level exceded 1 ppm (respectively 1.4 and 9.7). Dieldrin levels in livers of 13 fish-eating birds (8 cormorants and 5 pied Kingfishers) collected near the shoreline sprayed, varied from 0.03–1.81 ppm (all data on a wet weight basis). In 15 larger fish (Tilapia esculenta, Alestes jacksoni and Clarias mozambicus) dieldrin residues (total body or lateral muscles) varied from 0.009–0.086 ppm (Koeman et al., 1969).
Table 3.2 Residues of dieldrin in the livers and brain of birds which were found dead or dying in the Wandere Valley
|Species||Sex||Date||Residue in ppm|
In the Lambwe Valley (Nyanza Province) the possible hazards to game animals resulting from aerial dieldrin applications for tsetse control were studied in the years 1970–72. The uptake by game animals of dieldrin and its photo-isomerizations product photodieldrin, as well as residues in grass and soil, were determined immediately after spraying and in a 15–24 month period after the last date of aerialdieldrin-applications. It is reported that for this reason various game animals up to a total of 164 individuals were shot and their livers and brain analysed for chemical residues (Richardson, 1970; Baldry, personal communication).
In many samples the residue of dieldrin was lower than the limit of detection of 0.01 ppm whilst the mean liver residue of the other samples (comprising Reedbuck, Oribi and Hyena) amounted to 0.223 ppm (range 0.010–4.4 ppm). The results are comparable to those of the rodent analyses referred to above, and indicate that both the groundspray ans aerial spray procedures concerned do not give rise to a significant contamination of the grass and shrubs on which the larger game animals feed. Apparently the hyena's in the area also do not feed on contaminated food organisms.
Most studies concerning the environmental impact of tsetse control by chemicals means, are reported from Nigeria. Figure 3.1 shows the areas where the studies were carried out.
In 1960 fish-eating birds were collected along the shore of Lake Chad and the estuary of the Yobé river in the lake. The aim was to measure residue levels of DDT and its metabolites (in particular DDE). In the previous period from 1956 to 1966 tons of DDT had been applied on the Komadugu Gana/Yobé river system for the control of G. tachinoides and G. morsitans submorsitans (Davies, 1964, 1971). The DDE levels in the livers of 15 Cormorants and Pied Kingfishers varied from 0.012 to 0.17 ppm indicating that at that time the level of contamination of the estuary and the lake was relatively low (Koeman and Pennings, 1970).
Acute and long-term effects of discriminative groundspray applications of dieldrin were studied in a fringing forest habitat in the Sudan Savanna near Potiskum (area 2, Fig. 3) The study was carried out in 1969 and 1970. The results showed that the application of diel-drin was associated with acute deaths of many wild animal species including among others insects, fish, birds (especially insectivorous species) and certain mammals (e.g. bats, squirrels). The increased death rates could be correlated with a marked decline of the population density of certain species. Observations carried out one year after spraying showed that almost all species of mammals, birds, reptiles and amphibians included in the census before and at the time of spraying had survived and that many of the depleted species showed signs of recovery; the latter very probably being due to immigration of individuals from adjacent unaffected areas. However, some species of insectivorous birds characteristic for the fringing forest biome were still present in low density as compared to prespraying conditions and control areas, while a few apparently had reached the point of local extinction (e.g. the White-crowned Robin-Chat, Cossypha albicapilla (Vieillot) and the Blue-breasted Kingfisher, Halcyon malimbicus (Shaw)). Dieldrin levels discovered in the brains of birds found dead varied from 2.2 to 16 ppm (wet weight basis). In general in birds, amphibians and fish collected one year after spraying the residue levels of dieldrin were low and very probably did not represent a toxic hazard for the animals analysed.
Fig. 3.1. Map showing study areas
In the period from 1974 to 1976 side-effect studies were made of helicopter applications of dieldrin and endsulfan and groundspray applications of endosulfan and DDT. These studies were carried out on three locations in the Northern Guinea Savanna Zone. It was found that all applications concerned may give rise to mortality in many non-target species. After helicopter application the period in which mortality occurred in birds, mammals, reptiles, amphibians, fish and non-target insects amounts to 2 to 3 weeks in the case of dieldrin and approximately 1 week in the case of endosulfan. It seems that endosulfan causes slightly more damage to coldblooded vertebrates than dieldrin, while on the other hand certain warmblooded species are much less susceptible for endosulfan than for dieldrin. The insect mortality as found after aerial dieldrin and endosulfan applications is indicated in tables 3.3 and 3.4. Insects were caught on two 4 square metre blanket sheets in each area respectively (Koeman et al., 1976). When a comparison is made with the former studies in which the side-effects of dieldrin groundspray applications were concerned the conclusion can be drawn that helicopter aerial applications affect a wider range of bird species than discriminative groundspray applications. Certain species appeared to be very vulnerable and either were not recorded anymore or became extremely rare in the areas treated. Certain mammalian species were also affected by the spraying operations and their numbers markedly reduced (e.g. Tantalus monkeys after aerial applications of dieldrin and Fruit Bats after aerial applications of endosulfan).
Table 3.3. Numbers of insects and spiders found dying or dead on blanket sheets following helicopter spraying with diel-drin in area (4) in 1975-
|Hymenoptera (with exception of Formiciodea)||2||7||4||3||2||6||1||4||1||30|
|Heteroptera + Homoptera||2||7||7||5||7||4||1||33|
Table 3.4. Numbers of insects and spiders found dying or dead on blanket sheets following helicopter spraying with endosulfan in area (4) in 1975
|Hymenoptera (with exception of Formicoidea)||30||6||1||4||1||42|
|Heteroptera + Homoptera||22||22||7||1||1||2||55|
A preliminary investigation was made on the environmental effect of ULV fixed-wing applications of endosulfan. This study was carried out in the Southern Guinea Savanna zone in the Doma Forest Reserve (area 6, Fig. 3).
No adverse effects on wildlife (including birds, mammals, reptiles, amphibians, fish and non-target insects) were observed during and after the spraying operations. Therefore the preliminary conclusion can be drawn that this method very probably is less deleterious to wildlife than the helicopter application of endosulfan tried out experimentally in other parts of Nigeria (Takken et al., 1976). However it appears that the eradication of G. palpalis was not fully successfull, as the fly population-density has only been reduced for a relatively short period (Tsetse and Trypanosomiasis Division, personal communication).
The environmental impact of 8 to 10 years dieldrin application in Eastern Ankole (western Region) is reported by Sserunjoji and Tjell (1971) and Sserunjoji (1973). Chemical analyses were made of samples from soil and grass. The sampling areas were all treated with a selectively applied dosage of 3% dieldrin water emulsions (average deposit 98 g a.i. per hectare) only once. Dieldrin residues in soil varied from 0.006 to 0.029 ppm, whilst residues in grass varied from 0.93 to 0.11 ppm. Residues in both soil and grass were in general inversely proportional to the time of application (Sserunjoji and Tjell, 1971).
In this country side-effects of dieldrin applications using knapsack and Unimog mist-blower spraying devices were studied in the years 1962–1964. Potential tsetse resting sites along road verges and on all trees lining access tracks, including rot holes in trees, overhanging branches and fallen logs were sprayed. Also holes in the ground, particularly those of the antbear Orycteropus afer (which proved to be important resting and breeding sites of tsetse) were treated.
Dead and dying animals were collected, incidentally only, which included mammals, birds, reptiles and fish. In Table 3.5 mammals which died as a result of the dieldrin applications are listed. It is reported that the Hyenas very probably died due to their feeding on Elephant meat which was contaminated with dieldrin by accident. A total of 38 birds representing 24 species were found dead or dying, among which 15 insectivorous species were counted. It is further reported that a large number of various reptiles were collected, viz. 17 snakes and 101 lizards. Due to an incident (washing of empty Dieldrix T15 tins in a dam) a total of 223 dead fish were found within a week after the incident, all were Tilapia species (Wilson, 1972).
Studies on the side-effects of ULV fixed-wing endosulfan applications in Barotse Province (south-west Zambia) were carried out in 1968. Emphasis was laid mainly on non-target insect species by means of 1) ground observations immediately after spraying; 2) measurement of the insect ‘fall-out’ of trees with a dense insect concentration and 3) observations of a predator (Dragonfly) species population. In no occasion any dead or dying animal was found and a reduction in the abundance of species or population density was not observed. Insect collections made in sprayed and unsprayed areas revealed a total of subsequently 163 and 159 different species (Magadza, 1969).
Table 3.5. Mammals found dead after dieldrin applications with groundspray (mistblower) devices (after Wilson, 1972)
|Scientific name||Common name||No.|
|Galago senegalensis||Night ape (lesser Galago)||7|
|Heterohyrax brucei||Yellow spotted Dassie||2|
|Crocuta crocuta||Spotted Hyena||3|
|Canis sp.||Domestic Dog||1|
|Paraxerus cepapi||Bush Squirrel||5|
The conclusion can be drawn that most ground and aerial applications of pesticides commonly used in tsetse control and eradication programmes may cause appreciable mortality in many non-target organisms (vertebrates as well as invertebrates). Although the observations made during various side-effect studies show the ultimate survival of most of the species considered in these studies, certain species such as insectivorous birds either do not recover quickly or virtually disappear. As only selective species of organisms were included in the animal census it is most likely that many more species were affected than those for which a strong and sometimes a fatal decline was recorded. In particular when very large areas are treated with insecticides in a relatively short period of time certain species may not be able at all to recover and hence are likely to become eliminated completely from the areas concerned. This is most likely for species which are confined or almost confined to certain habitats like the fringing forest and similar biomes which in most cases also form the dry season habitat for the tsetse flies. In general it has been found that the present helicopter applications affect a wider range of species than discriminative groundspray applications. However, as can be judged from the spectrum of species found among the victims, the most hazardous method of pesticide application in connection to tsetse control very probably is the ground use of mistblowers (e.g. Unimog) or comparable equipment (Graham, 1964; Wilson, 1972).
The least hazardous method reported so far seems to be the so-called knock-down method in which low dosages of endosulfan have been applied in ultra-low volume formulation by means of fixed-wing aircraft. In Botswana and Nigeria no serious side effects were observed after application of this method. However, it is not known yet whether this method is applicable in all tsetse habitats.