Selective use of odour-baited, insecticide-treated targets to control tsetse flies Glossina austeni and G. brevipalpis in South Africa

The effectiveness of odour-baited targets treated with 0.8% deltamethrin in controlling Glossina austeni Newstead and G. brevipalpis Newstead (Diptera: Glossinidae) was evaluated in Zululand, South Africa. Targets were initially deployed in the three habitat types (grassland, woodland and forest) of two adjacent areas at a density of four targets per km(2). One area functioned as the treatment block (c. 35 km(2)) and included the focus of the target deployment, and the second area functioned as a barrier block (c. 40 km(2)) against tsetse fly re-invasion from the untreated area to the south. After 8 months, targets were removed from open grassland in both areas and target density in wooded habitats and sand forest was increased to eight per km(2). Twelve months later, all targets were removed from the barrier block and used to increase target density in the wooded and sand forest habitats of the treatment block to 12 per km(2). This target density was maintained for 14 months. In the treatment area, a 99% reduction in G. austeni females occurred after 13 months at a target density of eight per km(2) in wooded habitat; this was maintained for 22 months. Reduction in G. brevipalpis was less marked. The relatively poor reduction in G. brevipalpis is attributed to the high mobility of this species and its distribution throughout less wooded and more open habitats.     

Seasonal variations in the distribution and abundance of the tsetse fly,Glossina morsitans morsitans in eastern Zambia

The seasonal changes in the distribution of Glossina morsitans morsitans Westwood (Diptera: Glossinidae) and its main host, cattle, were examined in a cultivated area of the plateau of eastern Zambia. During four consecutive years, the tsetse and cattle populations were monitored along a fly-round transect traversing the two main vegetation types in the study area. These were miombo, a one-storied open woodland with the genera Brachystegia and Julbernardia dominant, and munga, a one- or two-storied woodland where the principal tree genera were Acacia, Combretum and Terminalia. Concurrently, a capture/mark/release/recapture (CMRR) exercise was conducted along two other transects also traversing both vegetation types. The index of apparent abundance of tsetse (IAA) in miombo increased at the beginning of the rainy season (November), reached its peak at the end of the rainy season (April) and was low during the cold season (May to late August), but especially the hot dry season (September to late October). The IAA of tsetse in munga showed a pattern that was the reverse of that in miombo. The seasonal changes in the IAA of tsetse in both vegetation types were in accordance with changes in the movement patterns of tsetse between the two vegetation type as observed using CMRR. The distribution and abundance of cattle along the transect also showed a seasonal trend. This was especially so in munga, during the first three years of observations, where cattle abundance increased gradually from June onwards, reached a maximum at the end of the hot dry season (October-November) and declined steeply at the start of the rainy season (November-December). In both vegetation types, the monthly mean IAA of tsetse was positively correlated with the abundance of cattle in the previous month. It is concluded that the distribution of tsetse in cultivated area of the eastern plateau of Zambia undergoes substantial seasonal changes, which can partly be attributed to changes in the distribution of cattle. The implications of these observations for the control of tsetse are discussed.     

Genetics of hybridization of Glossina swynnertoni with Glossina morsitans morsitans and Glossina morsitans centralis

Abstract Reciprocal crosses were performed with Glossina swynnertoni and Glossina morsitans morsitans and with G. swynnertoni and Glossina morsitans centralis , using strains that carried marker genes in all three linkage groups. Glossina swynnertoni males can inseminate, but not fertilize, G.m.morsitans; all other crosses produced some fertile females. Hybridization did not cause sex ratio distortion among F_{ flies. Most F and backcross females were fertile, but all F, males were sterile. Sterility among backcross males was also high (99% in BXj, 85% in Bx₂, and about 50% in Bx₃ to Bx₅). Chromosome transmission by hybrid females usually conformed to Mendelian expectations, but genetic recombination was lower than observed in G.m.morsitans. The reduction in fertility among backcross females was not associated with heterozygosity in any linkage group. Sterility among hybrid and backcross males was associated with heterozygosity of sex chromosomes and probably autosomes. The results support the systematic placement of G.swynnertoni closer to G.mxentralis than to G.m.morsitans.     

Juvenile hormone mimics as effective sterilants for the tsetse fly Glossina morsitans morsitans

The development of puparia of Glossina morsitans morsitans Westwood was disrupted by topical applications of the juvenile hormone mimics S-methoprene (the resolved enantiomer of 11-methoxy-3,7,11-trimethyl-2,4-dodecadienoic acid 1-methyl ester) (Zoecon), S21149 (propionaldoxime-0-4-phenoxyphenoxyethylether) (Sumitomo), or S31183 (2-[1-methyl-2-(4-phenoxyphenoxy)ethoxy]pyridine) (Sumitomo) dissolved in acetone. Puparia so treated during the first 4 days of life suffered developmental abnormalities, the severity of which were dose-dependent. Similarly, puparia produced by adult females treated with these compounds were abnormal. Dose-response data showed that effects were greatest with S31183 and least with S-methoprene. Abnormalities in the form of abdominal lesions and wing crumpling were typical of flies emerging from puparia produced by S-methoprene-treated females. However, arrested development at the red eye and pigmented seta stage within the puparium were typical of offspring of females treated with S21149 and S31183. A dose of 2 micrograms per female of S31183 was sufficient to prevent emergence of offspring produced for the rest of the life of the fly. The same dose resulted in partial recovery of females treated with S21149 some 18 days following treatment. Treatment with 2 micrograms S-methoprene did not suppress completely the production of normal offspring and recovery was complete some 27-35 days after treatment. Exposure of males to 20 micrograms S31183 did not impair their ability to inseminate females; transfer of material during copulation was sufficient to prevent the production of viable offspring by their mates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of temperature changes on larviposition rhythm in the tsetse fly, Glossina morsitans

ABSTRACT. The hourly and quarter-hourly distribution of larval deposition by female Glossina morsitans Westw. was studied at various temperatures. At constant temperature and humidity, peak larviposition occurred 8–9 h after lights on. The effect of confining the flies to daily (LD 12:12 h) regimes of at least twenty-five consecutive cycles that included a sudden increase in temperature of c. 6°C for 2 h was a significant reduction in depositions during each period of increased temperature, and a significant increase before the heat impulse. When the temperature was allowed to fall rapidly, larviposition rate doubled in the following 15 min.     

Performance of the tsetse, Glossina morsitans morsitans reared under various feeding regimens in Zambia

Groups of Glossina morsitans morsitans Westwood fed at emergence and thereafter daily, every second or third day respectively, up to the end of their first pregnancy cycle, survived well (73–79%) and produced virtually the same number of puparia/ (0.83–0.85) in the same puparial weight class (23–24 mg). However, adult survival (29%), number of puparia/ (0.30) and puparial weight (19 mg) were much lower in the group consistently fed every 4th day after the initial meal at emergence. It is proposed that tsetse colonies could be fed on Mondays, Wednesdays and Fridays without jeopardising adult survival, puparial production/ and the size (weight) of puparia produced.

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Performances en Zambie de la mouche Tsé-Tsé (Glossina morsitans morsitans) élevée en utilisant différents régimes alimentaires

Résumé Afin d'estimer si une alimentation quotidienne de G. morsitans morsitans présente un avantage sur une alimentation moins fréquente, nous avons enrigestré la survie des adultes, la production et le poids des pupes chez des individus nourris à l'émergence et, ensuite, tous les jours ou tous les 2, 3 ou 4 jours. Les femelles alimentées quotidiennement, ou tous les 2 ou 3 jours, ont produit le même nombre de pupes (0,83–0,85), avec des poids de même ordre (23–24 mg), et avec une aussi bonne survie (73 à 79%). Alimentées tous les 4 jours, elles ont produit 0,30 pupe/femelle, pesant 19 mg/pupe et avec une plus faible survie (29%). Ces résultats montrent qu'il est inutile de nourrir les mouches chaque jour au lieu de tous les 2 ou 3 jours. Cependant une alimentation à des intervalles supérieurs à 3 jours, a eu des conséquences clairement défavorables. Ainsi, peuvent être considérablement réduits et le travail et le coût des élevages, sans porter préjudice à la production, en alimentant les mouches 3 fois par semaine, par ex. les lundis, mercredis et vendredis.

     

Responses of tsetse flies, Glossina morsitans morsitans and Glossina pallidipes, to baits of various size

Recent studies of Palpalis group tsetse [Glossina fuscipes fuscipes (Diptera: Glossinidae) in Kenya] suggest that small (0.25 × 0.25 m) insecticide-treated targets will be more cost-effective than the larger (≥1.0 × 1.0 m) designs currently used to control tsetse. Studies were undertaken in Zimbabwe to assess whether small targets are also more cost-effective for the Morsitans group tsetse, Glossina morsitans morsitans and Glossina pallidipes. Numbers of tsetse contacting targets of 0.25 × 0.25 m or 1.0 × 1.0 m, respectively, were estimated using arrangements of electrocuting grids which killed or stunned tsetse as they contacted the target. Catches of G. pallidipes and G. m. morsitans at small (0.25 × 0.25 m) targets were, respectively, ～1% and ～6% of catches at large (1.0 × 1.0 m) targets. Hence, the tsetse killed per unit area of target was greater for the larger than the smaller target, suggesting that small targets are not cost-effective for use against Morsitans group species. The results suggest that there is a fundamental difference in the host-orientated behaviour of Morsitans and Palpalis group tsetse and that the former are more responsive to host odours, whereas the latter seem highly responsive to visual stimuli.     

Lifetime changes in the nutritional characteristics of female tsetse Glossina pallidipes caught in odour-baited traps

Female Glossina pallidipes Austen were captured in odour-baited traps at Rekomitjie Research Station, Zambezi Valley, Zimbabwe during February 1994; 2890 were dissected and assigned to their ovarian age category and day of pregnancy using the lengths of the oocytes and uterine content. For 1838 of these flies, the nutritional state of the mother and her uterine content were estimated separately. It was thereby possible to see how, during pregnancy, the females acquired fat and residual dry weight (RDW) and transfered them to the larva. Newly emerged flies contained 1 mg fat and 6 mg RDW, of which 4 mg was in the thorax (TRDW). Fat hardly increased by the first ovulation; RDW increased by 2.5 mg and 1.5 mg of this increase was in TRDW. Mean haematin levels increased from 2 to 8 microg during each pregnancy. Fat increased from 1.2 mg to 4.5-5 mg by day 7 and was then rapidly transferred to the larva. RDW increased by only 1.8 mg by day 7, but larval RDW increased thereafter by > 6 mg. Amino acids from late-pregnancy bloodmeals are incorporated directly, in the uterine gland, into 'milk' that is taken up rapidly by the larva. Capture probability was highest on day 1 of pregnancy, when nutritional levels were lowest, with lesser peaks on days 5 and 8 when the fly was nourishing a rapidly developing larva. On day 1, the peak of the logarithm of the haematin distribution corresponded to flies estimated to have fed approximately 75 h previously; by day 8 it had shifted to approximately 60 h post-feeding. A model in which feeding rates and capture probabilities increased exponentially with time since feeding accounted for 97% of the variance in log haematin frequencies. On 4/9 days of pregnancy there was no significant decline in fat with haematin content during the lipolytic phase. The rate of decline is not a satisfactory estimate of the rate of fat usage. Flies in this study had longer wings and higher TRDW than those from refuges in an earlier study, but had lower levels of fat and haematin.     

Activity patterns in pregnant tsetse flies, Glossina morsitans

ABSTRACT. Actograph measurements of the spontaneous flight activity of isolated female Glossina morsitans morsitans Westw. were made through their first two pregnancy cycles in constant conditions under LD 12:12. Activity fell from a mean of c. 20 units/day to near zero during the 24 h preceding the day on which larvipositionoccurred. Activity on the day of larviposition rose significantly, to c. 35 units/day, then fell back to the baseline 20 units on subsequent days. The circadian pattern of activity was changed markedly by larviposition: 48 h before it, activity in the morning peak of the usual V-shaped diel pattern was twice normal; over 70% of the flies then fed, and the evening arm of their V disappeared; 24 h before larviposition, most flies were totally inactive, the few that did fly performing only 1 or 2 units/day, and only in the first and last hours of the photophase; on the day of larviposition, the morning peak of the V was reduced by c. 70%, and activity peaked instead during the post-noon 2–3 h, before and during the act of parturition. Almost all larvipositions occurred between noon and lights-out. It is suggested that the c. 48 h of pre-larviposition quiescence may play a role in the fact that pregnant G. morsitans females often survive non-residual aerosol insecticide campaigns.     

The roles of vision and olfaction in mate location by males of the tsetse fly Glossina morsitans morsitans

The roles of visual and/or olfactory stimuli in eliciting mating responses from male Glossina morsitans morsitans Westwood were examined, using a system for automatically recording the number and duration of mating strikes made towards decoys, under controlled conditions. The results confirm that there is no olfactory component of the female sex recognition pheromone sensed by the male antennae, and the attraction of males to females appears to be visual. The absence of male-male mating strikes was the result of the absence of female sex-pheromone, rather than the presence of a repellent mating deterrent in the male cuticle. Experiments with coloured, artificial, sex-pheromone-dosed, cotton decoys showed that colour had only weak effects on attractiveness and number of encounters with decoys, and that no colour caused significant enhancement of mating responses over those shown to decoy females.     

Cloning and expression of the yolk protein of the tsetse fly Glossina morsitans morsitans

Two major families of nutritional proteins exist in insects, namely the vitellogenins and the yolk proteins. While in other insects only vitellogenins are found, cyclorraphan flies only contain yolk proteins. Possible sites of yolk protein synthesis are the fat body and the follicle cells surrounding the oocyte. We report the cloning of the yolk protein of the tsetse fly Glossina morsitans morsitans, a species with adenotrophic viviparity. The tsetse fly yolk protein could be aligned with other dipteran yolk proteins and with some vertebrate lipases. In contrast to the situation in most fly species, only a single yolk protein gene was found in the tsetse fly. Northern blot analysis showed that only the ovarian follicle cells, and not the fat body represents the site of yolk protein synthesis.     

Microsatellite diversities and gene flow in the tsetse fly,Glossina morsitans s.l

Tsetse flies occupy discontinuous habitats and gene flow among them needs to be investigated in anticipation of area-wide control programs. Genetic diversities were estimated at six microsatellite loci in seven Glossina morsitans submorsitans Newstead (Diptera: Glossinidae) populations and five microsatellite loci in six G. m. morsitans Westwood populations. Nei's unbiased diversities were 0.808 and 76 alleles in G. m. submorsitans and 0.727 and 55 alleles in G. m. morsitans. Diversities were less in three laboratory cultures. Matings were random within populations. Populations were highly differentiated genetically. Populations were strongly subdivided, as indicated by fixation indices (F(ST)) of 0.18 in G. m. morsitans and 0.17 in G. m. submorsitans. 35% of the genetic variance in G. m. submorsitans was attributed to differences between populations from The Gambia and Ethiopia. All available genetic evidence suggests that genetic drift is much greater than gene flow among G. morsitans s.l. populations.     

The efficacy of various pyrethroid insecticides for use on odour-baited targets to control tsetse

The efficacy of various pyrethroid insecticides for use on odour-baited targets to control tsetse was compared in Zimbabwe. Formulations were applied to cotton cloth and polyester net and, at various intervals, the materials were bioassayed by exposing fed female Glossina pallidipes (Austen) (Diptera: Glossinidae) to cloth for 45 s or by inducing them to collide briefly with net. Trial formulations were compared with deltamethrin suspension concentrate (s.c.), the insecticide currently used in tsetse control operations in Zimbabwe. Applying 0.8% suspension of alphacypermethrin to cloth or net produced high mortalities for 9 months which was similar in performance to 0.4% suspension of deltamethrin s.c. Deltamethrin s.c. and beta-cyfluthrin s.c. applied to cloth as 0.1% suspensions were equally effective, producing high mortalities for 2 months during the wet season, and 0.8% suspension of beta-cyfluthrin was effective for 12 months. Suspensions of 0.1% lambdacyhalothrin capsule suspension or 0.1% lambdacyhalothrin wettable powder were significantly less effective than 0.1% deltamethrin s.c. Chemical analyses showed that increasing the concentration of insecticide applied to material increased the initial amount of insecticide on the material and decreased the subsequent rate of loss; 0.1% suspension of beta-cyfluthrin s.c. applied to cloth produced an initial concentration of approximately 280 mg/m2 which declined by 94% in 12 months whereas 0.8% suspension showed no significant decrease in concentration (mean= 1304 mg/m2) over the same period. For controlling tsetse by means of pyrethroid-treated targets, it is suggested that beta-cyfluthrin s.c. is as effective as deltamethrin s.c. but that alphacypermethrin s.c. should be used at twice the concentration of deltamethrin s.c. to obtain the same performance.     

Performance of the tsetse fly Glossina pallidipes reared under simple laboratory conditions

A simple grass-thatched hut was used to rear Glossina pallidipes Austen. Constructed to allow free flow of air, the temperature and humidity inside correspond to that of the outside environment. Pupae used to start the colony were obtained from pregnant females from Lambwe Valley, Western Kenya. Nine day-old females were paired with 12 day-old males for 7 days after which they were separated.Colony performance was evaluated on the basis of female survival, number and weight of puparia produced, and mortality rates. The emergence rate of puparia weighing more than 30 mg was above 80%. Data on the performance of the colony between June 1985 and June 1986 are presented. We suggest that the simple nature of the rearing facility and its direct contact with the outside environment have facilitated the colonization of the flies.

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Résumé Une cage très simple, conçue pour assurer l'arrivé d'air, et le maintien de l'humidité et de loa température extérieure, a été employée pour conserver et élever G. pallidipes. Les pupes utilisées pour constituer la souche provenaient de Lambwe valley (ouest du Kénya). Des couples de femelles vieilles de 9 jours et de mâles de 12 jours ont été consitués, les sexes ont ensiute été séparés. La performance de la souche a été estimée en fonction de la survie des femelles et du nombre et du poids des pupes produites, et des taux de mortalité. Plus de 80% des pupes ont pesé 30 mg et plus, et le taux d'émergence a été de 80%. Les résultats fournis concernent les performances observées entre juin 1985 et juin 1986. Nous estimons que la simplicité du dispositif d'élevage et le contact direct avec les conditions écologiques externes ont facilité l'éstablissement de la souche.

     

Experiments on the elimination of symbionts from the tsetse fly,Glossina morsitans morsitans (Diptera: Glossinidae), by antibiotics and lysozyme

One sulfonamide and ten antibiotics were tested for symbiont elimination in Glossina morsitans morsitans. Only tetracycline, penicillin, and kanamycin could be used in concentrations which destroyed the symbionts and impeded host reproduction, but did not affect host longevity. The later the treatment with penicillin and kanamycin began, the smaller was the damage to symbionts from these two antibiotics. Small doses damaged the symbionts to an extent that flies could produce offspring, but these were free of symbionts. Lysozyme was used as an alternative to antibiotics. After both injection and oral administration of lysozyme the symbionts were damaged, and host reproduction ceased, although host longevity remained unaffected. It can be concluded from the results of these experiments that tsetse flies do not require their symbionts for survival but probably do need them for reproduction.     

Copulatory behaviour of the tsetse flies Glossina morsitans and G.austeni

ABSTRACT. The copulatory behaviour of Glossina morsitans morsitans West. and G.austeni Newst. was analysed by filming. After a male and female engaged genitalia, the male performed a repertoire of five actions for 3–4 min: (1) 'rubbing' his metathoracic, tibiotarsal joint against the region of genital contact; (2) 'stroking' or hitting the female's head and thorax with his meso- and metathoracic legs; (3) 'wing flick' by moving his mesothoracic legs in a rowing motion whilst at the same time vibrating the wings as in normal flight; (4) 'wing vibration' with the wings vibrated in the closed position; (5) 'wings out' in which the wings are moved out to the flying position without any observable vibration. Each action was repeated many times, to give variable individual sequences, but declined in frequency exponentially over the first 3–4 min in copulo. The two species differed in the frequency of acts. Shortly before separation, a few hours later, actions 1 and 2 reappeared. Receptive females exhibited little overt behaviour except in the maintenance of a passive stance. Refractory females rejected a mating attempt by flexing the abdomen ventrally, vibrating their wings in the closed position, and pushing the male with meso- and metathoracic legs. The significance and possible functions of male behaviour are discussed in relation to mating in Glossina and other Diptera.     

Spectral sensitivity and flicker fusion frequencies of the compound eye of salmon and wild-type tsetse flies, Glossina morsitans

ABSTRACT. The spectral sensitivity and flicker fusion frequency (FFF) of wild-type and salmon Glossina morsitans morsitans Westwood (Diptera, Glossinidae) were compared electroretinographically (ERG). Spectral sensitivity curves were similar in shape for dark-adapted wild-type and salmon flies, but salmon flies were over 100 times as sensitive as wild-type flies over much of their sensitivity range. Estimation of the spectral absorption curve (from the differences in ERG sensitivities) for the pigment absent from (or present in low concentration in) the salmon eye suggests that the pigment is an ommochrome. FFF at threshold light intensities was similar in wild-type and salmon flies, but at higher light intensity (1.3 °W/cm²) the FFF of salmon flies increased c. 200–300%, due to the capacity of the salmon eye to adapt rapidly to the flicker stimulus. Body weight had little effect upon spectral sensitivity and FFF. Wild-type males were more sensitive to yellow-green light and had higher FFF than did wild-type females. Salmon males and females did not differ in spectral sensitivity, but females had higher FFF (when tested with 520-nm light) than did males. Old wild-type females did not differ from young females in either spectral sensitivity or FFF. However, old salmon females were more sensitive but had lower FFF than young salmon females. Food deprivation reduced spectral sensitivity and FFF in wild-type males but not in salmon males. Irradiation (10.5 krad) reduced spectral sensitivity ( c. 75–375%) and FFF ( c. 30%) in wild-type males. The greatly increased spectral sensitivity and FFF in salmon flies indicate that these flies may behave differently from wild-type flies in the field. Differences in the way spectral sensitivity and flicker discrimination are affected by dark and light adaptation, and by such factors as age and sex, indicate that these measurements are of two independent phenomena.     

The sunset activity of tsetse flies: a light threshold study on Glossina morsitans

ABSTRACT. At dusk, tsetses fly from their day-time resting sites on tree trunks to spend the night on leaves and twigs. At the end of the day in the laboratory, they show a few minutes of heightened activity which apparently represents this behaviour. This occurs immediately after lights-out in a square-wave LD cycle, but just before the end of a 30-min artificial 'dusk' which mimics the natural change in light intensity at sunset. The activity is triggered when the declining light falls to a mean value of c. 350 mW m^-2. Accurate, 24-h light measurements made in Zimbabwe show that in tsetse 'bush' this intensity occurs close to sunset. Neither the initial photophase light intensity (900 and 2500 mW m^-2 were tested) nor the rate of dimming affect the critical value, which is also the same whether arrived at within c. 10 min in a 'logarithmic dusk' or within c. 20 min in a 'linear dusk'. In newly-emerged or recently fed flies, however, it is lower ( c. 50–100 mW m^-2); and when a similar activity burst is induced by a 'dusk' at midday (i.e. at the flies' phase of minimum activity), the threshold is c. 200 m W m^-2. It is concluded that this short behavioural programme is primarily a direct response to a specific, low light intensity, but that the threshold is modified by circadian and other physiological inputs.