Characterization of the sexual responses of male tsetse flies, Glossina morsitans morsitans, to pheromone-baited decoy 'females' in the field

ABSTRACT. The sexual behaviour of male Glossina morsitans morsitans Westwood (Diptera: Glossinidae) towards decoys dosed with sex phero-mone (15,19,23-trimethylheptatriacontane) is described quantitatively from field observations. The flies responded with a standard behavioural pattern after landing. This involved: first, the perception of pheromone; second, orientation on the decoy and genitalia engagement; and third, a lengthy quiescence corresponding to natural copulation. The probability of a fly leaving a decoy decreased during the sequence and was least in the final 'copulatory' phase, when it remained constant under constant conditions. The initial, rapid rates at which flies left decoys were affected mostly by pheromone dose: the lower the dose, the higher the rate. The final, slow rate of leaving was unaffected by pheromone dose, being most affected by environmental stimuli, especially interference from other flies: at high fly densities, final rates of leaving were high. The results are discussed in the context of improving the potential for using pheromone and chemo-sterilant-dosed decoys for tsetse autosterilization.     

Olfactory responses of tsetse flies to phenols from buffalo urine

Abstract A comparison was made of the EAG responses of males and females of Glossina morsitans morsitans Westwood, G.austeni Newstead and G.tachinoides , Westwood to various doses of compounds known to be components of ox and buffalo urine fractions which are attractive to tsetse in the field (phenol, 3- and 4-methylphenol, 3- and 4-ethylphenol, 4-n-propylphenol, dimethylsulfone). All three species did not respond to dimethylsulfone. The overall responses to the phenolic substances were higher in females than in males in G.m.morsitans and higher in males than in females in G.austeni and G.tachinoides. Response spectra of the species for the phenolic substances suggested that G.m.morsitans and G. austeni were most responsive to 3- and 4-methylphenol and 3-ethylphenol, whereas G. tachinoides was most sensitive to 3-ethylphenol and 3-methylphenol, and only moderately sensitive to 4-methylphenol.
Cross-adaptation experiments, in which l-octen-3-ol, acetone, 4-heptanone and 3-nonanone were also included, revealed that all phenolic compounds stimulated one and the same class of receptors, which differed from the class of receptors activated by l-octen-3-ol. The ketones also had their own receptors. Hence, the flies can obtain information about the presence of attractants by at least three different receptor classes. It was concluded that phenol and any individual alkylphenol found in ox and buffalo urine should be attractive to tsetse flies, provided that stimulus intensity is above threshold and not beyond optimum. One class of receptors may respond more strongly in males than in females, whereas another class is more responsive in females than in males. This may result in a change in sex ratios in catches depending on the odour bait used.     

Selection of susceptible and refractory lines of Glossina morsitans centralis for Trypanosoma congolense infection and their susceptibility to different pathogenic Trypanosoma species

Abstract .In a single generation of selection, two lines of Glossina morsitans centralis were established that differed significantly in susceptibility to Trypanosoma congolense clone IL 1180. Reciprocal crosses demonstrated that susceptibility was a maternally inherited trait. Differences between the lines, to all phases of the trypanosome infection, were maintained for eight generations, whereas differences in susceptibility to midgut infections were maintained for twenty-eight generations. Thereafter, the lines did not differ in susceptibility to Trypanosoma congolense IL 1180. Susceptibility to infections with Trypanosoma congolense IL 1180 was only a weak predictor of susceptibility to T. congolense clones IL 13-E3 and K60/1, as well as clone T. brucei brucei STIB 247-L. However, the susceptible and refractory lines displayed these phenotypes when tested with Trypanosoma vivax, indicating that the factors that affect susceptibility to trypanosomes are expressed both within and outside the midgut.     

A comparison of Glossina morsitans centralis originating from Tanzania and Zambia, with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility

wo laboratory strains of Glossina morsitans centralis originating from different fly-belts (one from Singida, in Tanzania, and the other from Mumbwa, in Zambia) were compared with respect to vectorial competence for pathogenic Trypanosoma species, genetic variation and inter-colony fertility. The vectorial competence of G.m.centralis of Tanzanian origin for Trypanosoma vivax and T.congolense is similar to, whereas for T.brucei brucei it is lower than the colony of Zambian origin. Nevertheless, these two laboratory strains of G.m.centralis showed levels of susceptibility to the three pathogenic Trypanosoma species which were much greater than previously observed in laboratory colonies of other Glossina species. Electrophoresis of fifteen enzymes revealed that the two colonies differ significantly in allele frequencies at only three loci that are relatively close together on one of the autosomes. Hybridization experiments revealed that G.m.centralis from the two fly-belts are consubspecific.     

Changes in temperature, not photoperiod, control the pattern of adult eclosion in the tsetse, Glossina morsitans

Abstract. The timing of adult eclosion in tsetse, an event that normally occurs in mid-afternoon, is regulated by the daily cycle of temperature elevation. If a temperature cycle is maintained, the rhythm of eclosion persists under continuous light or continuous darkness. Artificially shifting the temperature peak to the scotophase results in a concomitant shift in the eclosion pattern. Daily temperature variations as small as 0.4°C are sufficient to establish the rhythm. Eclosion activity tracks the temperature peak, even if the pulses are of short duration (4 h) or with irregular frequencies of 12 or 36 h. The temperature-induced rhythm offers a simple mechanism for separating females and males. Individuals that pupariate on the same day eclose as adults over a 4–5 day period at 25°C, and in such collections, females are the first to eclose. This distinction makes it possible to collect samples of predominately one sex, a feature that may facilitate the collecting of males for use in the sterile-male technique.     

Studies on Trypanosoma vivax: Transmission of mouse infective T. vivax by tsetse flies

Glossina morsitans and G. tachinoides were successfully infected with 2 isolates of Trypanosoma vivax which had an inherent property for serial maintenance in mice. The infection rate in the flies was relatively high. Cyclical transmission of these isolates from sheep to sheep and from goat to goat was achieved and did not affect the property of the isolates to infect mice. Mice were not apparently suitable for direct fly transmission experiments of T. vivax.     

Tissue distribution and prevalence of Wolbachia infections in tsetse flies, Glossina spp

Tsetse flies Glossina spp. (Diptera: Glossinidae) harbor three different symbiotic microorganisms, one being an intracellular Rickettsia of the genus Wolbachia. This bacterium infects a wide range of arthropods, where it causes a variety of reproductive abnormalities, one of which is termed cytoplasmic incompatibility (CI) that, when expressed, results in embryonic death due to disruptions in fertilization events. We report here that in colonized flies, Wolbachia infections can be detected in 100% of sampled individuals, while infections vary significantly in field populations. Based on Wolbachia Surface Protein (wsp) gene sequence analysis, the infections associated with different fly species are all unique within the A group of the Wolbachia pipientis clade. In addition to being present in germ-line tissues, Wolbachia infections have been found in somatic tissues of several insects. Using a Wolbachia-specific PCR-based assay, the tissue tropism of infections in Glossina morsitans morsitans Westwood, Glossina brevipalpis Newstead and Glossina austeni Newstead were analysed. While infections in G. m. morsitans and G. brevipalpis were limited to reproductive tissues, in G. austeni, Wolbachia could be detected in various somatic tissues.     

Feeding behaviour of Glossina pallidipes and g. morsitans centralis on Boran cattle infected with trypanosoma congolense or T. vivax under laboratory conditions

In field studies, tsetse flies (Diptera: Glossinidae) feed more successfully on cattle infected with Trypanosoma congolense Broden (Kinetoplastida: Trypanosomatidae) than on cattle infected with T. vivax Ziemann or uninfected cattle. Here we describe the first laboratory investigation of this phenomenon. In the first experiment, caged Glossina pallidipes Austen were fed for 1 and 5 min on a Boran steer infected with T. congolense clone IL 1180 and on an uninfected steer. Feeding success was recorded in this way five times over several weeks. The same protocol was subsequently used in three additional experiments with the following combinations: G. pallidipes and a steer infected with T. vivax stock IL 3913, G. morsitans centralis Machado and a steer infected with T. congolense, and G. morsitans centralis and a steer infected with T. vivax. The four experiments were replicated once, making eight experiments in total. In three experiments there was increased tsetse feeding success, measured at 1 min, after a steer became infected (T. congolense, two experiments and T. vivax, one experiment). Analysis of all data combined found no significant differences in tsetse feeding success on the different groups of cattle prior to infection, but after infection tsetse feeding success was significantly greater on the infected cattle (P< 0.001). Trypanosoma congolense infection led to a greater increase in tsetse feeding success than T. vivax infection. The increase in feeding success was not related to changes in the level of anaemia, skin surface temperature or parasitaemia. A possible explanation is the effects of trypanosome infection on cutaneous vasodilation and/or blood clotting in infected cattle. When allowed to feed for 5 min, nearly all tsetse engorged successfully and effects of cattle infection on feeding success were not found.     

Activation of three species of tsetse (Glossina spp.) in response to host derived stimuli

Recordings were made of the activation of hungry Glossina morsitans morsitans Westwood, G. pallidipes Austen, and G. austeni Newstead in response to odours from ox breath and ox urine, and a moving visual stimulus, in a wind tunnel. The spontaneous activity of G.m.morsitans was very low (less than 4% of males and 2% of females active per min during control periods). That of G.austeni and G.pallidipes was in the region of 20% except for G.pallidipes females when in excess of 40% were active during control periods. Addition of ox urine odours to the airstream had no effect on activity in any of the species investigated but addition of ox breath odours to the airstream significantly increased activity of G.pallidipes and of G.m.morsitans, although for the latter only approximately 12% of flies were active. For G.austeni the addition of ox breath odours resulted in a significant increase in activity of females but not of males. The moving visual stimulus resulted in a significant increase in the activity of both sexes of G.austeni and G.m.morsitans but no change in the activity of G.pallidipes. The low level of spontaneous activity and the low response to ox breath odours in a strain of G.m.morsitans maintained in the laboratory since 1969 was compared with a new colony of this species which originated from puparia collected in Zimbabwe in 1991. No differences in either spontaneous activity or the response to ox breath odour was recorded, but females from the new colony were significantly more responsive to a moving visual stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)