P. A. Langley

Sterilizing tsetse (Diptera: Glossinidae) in the field: a successful trial

The juvenile hormone mimic, pyriproxyfen, applied topically to female tsetse flies, Glossina morsitans morsitans Westwood and G. pallidipes Austen, effectively sterilizes them by arresting development of their offspring in the pupal stage. Between July and November 1989, 41 odour baited traps treated with pyriproxyfen were deployed near Rekomitjie Research Station, Zambezi Valley, Zimbabwe, in a 12.3 km 2 block of woodland habitat of G. m. morsitans and G. pallidipes. Tsetse entering the traps brushed against material dosed with 2 mg/cm 2 pyriproxyfen and were then allowed to escape. Emergence rates from pupae of the two species collected in the block fell to 30% and 2.7%, respectively, of control levels after three months. Of more than 750 pupae of each species dissected 78% and 94%, respectively, showed incomplete development. The average ovarian age category of female G. pallidipes sampled in the block doubled during the trial. This was due to immigration of older flies and the declining birth rate which, if sustained over a large area for a year, was estimated as sufficient to cause a population reduction to 10 −6 of its original level.

Physiology of tsetse flies ( Glossina spp.) (Diptera: Glossinidae): a review

Abstract Since no major review of the literature on tsetse physiology has hitherto been undertaken, relevant papers up to the beginning of 1977 are included in the present work. The physiology of Glossina is dealt with under three major headings; reproductive, developmental and nutritional events in the life of this haematophagous and viviparous insect are discussed in relation to general principles of insect physiology gained from the study of other genera. The role of adult maturation and the possible involvement of a sex pheromone in successful mating are considered. The difficulties of studying neuroendocrine function in relation to reproductive physiology in a viviparous insect, where reproductive and developmental events are not always separated chronologically, are emphasised. Nevertheless, the role of the neuroendocrine system in the control of such events as ovarian development, ovulation, parturition, pupariation and metamorphosis is considered, and the contribution that recent work on Glossina has made to an increased understanding of general principles in this field is discussed. Laboratory observations have demonstrated circadian components of behaviour in Glossina that can influence interpretation of field observations and likewise should influence the design of physiological experiments. Utilisation of nutritional reserves for larval growth and for flight activity has received considerable attention recently. The general pattern seems to be one of rapid mobilisation of blood-meal amino acids and the involvement of a large lipid reserve. The combined haematophagous and viviparous habit of Glossina has led to some interesting modifications of basic physiology particularly in regard to flight metabolism, female accessory gland function and Malpighian tubule activity. The relevance of physiological studies to current developments in the field of tsetse control is discussed and the importance of exploiting our knowledge in the quest for novel insecticidal techniques emphasised.

Survival and behaviour of tsetse flies (Diptera, Glossinidae) released in the field: a comparison between wild flies and animal-fed and in vitro-fed laboratory-reared flies

Male and female Glossina morsitans morsitans Westw. which emerged from puparia produced by animal-fed and in vitro-fed colonies in England were marked distinctively with non-toxic paint and released into a natural habitat of G. morsitans and G. pallidipes Aust. in Rhodesia. Concurrently, adults of both species which emerged from locally-collected puparia were marked and released. Recaptures from artificial refuges, odour attractants and mobile baits at periods up to 59 days after release and at distances up to 1800 m from the release site indicated no clear differences between native G. morsitans and the two laboratory-reared groups in respect of body size, amount of fat present at emergence, survival, dispersal, availability to a range of baits, diet, speed of taking a first meal, wing damage and insemination rate. Although the blood-meal identifications for marked female G. morsitans were similar to those for both sexes of unmarked flies, blood-meals from marked males showed a relatively high proportion of bovid identifications. Unmarked flies caught were generally older than marked catches. The ratio of females to males in unmarked samples (1:1 for G. morsitans , 2:1 for G. pallidipes ) was roughly double that in marked catches.

A field trial of pyriproxyfen-treated targets as an alternative method for controlling tsetse (Diptera: Glossinidae)

A juvenile hormone mimic (pyriproxyfen) was used with odour-baited targets to assess its suitability for controlling tsetse flies ( Glossina spp.). In August 1991, 41 odour-baited targets identical to those used with insecticide in tsetse control operations, were each treated with 4 g of pyriproxyfen and deployed near Rekomitjie Research Station, Zambezi Valley, Zimbabwe, in a 12.3 km 2 block of woodland habitat of Glossina morsitans morsitans Westwood and G. pallidipes Austen. After three months, emergence rates from puparia of the two species collected in the block fell to 34% and 20% of control levels; 50 and 70%, respectively, of puparia of the two species collected were found, on dissection, to show arrested development. Changes in mean ovarian age and wing-fray category in the tsetse population during the trial were due partially to the pyriproxyfen and partially to high mortality, in the larval/pupal stages and in young adult flies, which occurs each year in the hot/dry season. Chemical analysis of cloth samples indicated that after four months 68–85% of the pyriproxyfen had been lost, a large proportion apparently dripping off the bottom of the target. If the technical problem of persistence can be solved pyriproxyfen could substitute for pesticides in target-based tsetse control operations.

Formulation of pyriproxyfen, a juvenile hormone mimic, for tsetse control.

ABSTRACT. A topical dose, in 1 uJ acetone, of 0.02 |xg 2‐[l‐methyl‐2‐(4‐phenoxyphenoxy) ethoxy] pyridine, the juvenile hormone mimic pyriproxyfen (S‐31183, Sumitomo Chemical Co.), caused an adult female tsetse, Glossina morsitans morsitans Westwood, to produce non‐viable offspring for the whole of her life.

Determining the age of tsetse flies, Glossina spp. (Diptera: Glossinidae): an appraisal of the pteridine fluorescence technique

Standard curves for the regression of pteridine fluorescence in the head upon chronological age were constructed for laboratory-reared Glossina adults. Of the five species investigated, the technique was a reliable predictor of age in G. morsitans morsitans Westwood, G. pallidipes Austen, G. palpalis palpalis (Robineau-Desvoidy) and G. tachinoides Westwood, but was not reliable for G. austeni Newstead. Field-caught tenerals of both sexes of G. p. palpalis , field-caught teneral females of G. pallidipes and tenerals of both sexes of G. m. morsitans released on an island in Lake Kariba, Zimbabwe, had significantly higher pteridine fluorescence levels than tenerals hatched in the laboratory. However, the regression of fluorescence on age produced similar slopes for both laboratory-reared and field-caught flies. From this, it is concluded that estimates of the ages of field-caught flies can be corrected by simply subtracting the difference in fluorescence values between field-caught and laboratory-reared tenerals. In practice, this amounts to shifting the frequency distribution of different age categories to bring the youngest age group back to day zero. A comparison of the fluorescence technique and the ovarian dissection method of determining the ages of females showed that over a wide range of ages the former was at least as accurate as the latter and should be the technique of choice for most field investigations.

Hormone stimulated lipolysis and proline synthesis in the fat body of the adult tsetse fly, Glossina morsitans

G. morsitans fat cells incubated in vitro with l-[U-14C]-leucine incorporated the radiolabel, mainly into triglycerides. Aqueous extracts of corpora cardiaca, midbrain, or thoracic ganglion stimulated the release of radiolabelled material from prelabelled fat cells in vitro. Corpora cardiaca extracts were the most active, approx. 1 × 10−3 gland pairs/μl elicited the maximal response. At concentrations above 1 × 10−3 gland pairs/μl the activity of corpora cardiaca extracts was inhibited by a substance which could be removed by gel filtration. The stimulatory factor in nervous-tissue extracts was destroyed by proteolytic enzymes and was recoverable in a single peak by Sephadex G15 gel filtration. Results suggest that it is a peptide hormone produced mainly by the median neurosecretory cells of the midbrain with the corpora cardiaca being the site of storage and release. No hormone was detectable in fresh haemolymph, but it was found at high concentration in boiled haemolymph, implying the presence of a heat labile inhibitor. Under the in vitro conditions used the hormone stimulated the synthesis of proline from alanine and the hydrolysis of triglycerides to free fatty acids. The probable functions of the hormone are to stimulate proline synthesis in response to demand for flight and/or to mobilise lipid for larval nutrition. The relative importance of these apparent functions in vivo could not be determined.

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

Abstract. 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 μg 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 μg 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 μg 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.

Maturation of the tsetse fly Glossina pallidipes (Diptera: Glossinidae) in relation to trap-orientated behaviour

ABSTRACT The fat free dry weight or residual dry weight of the thorax (Trdw) increased linearly for the first 10 days of adult life in both sexes of G.pallidipes in the laboratory as their flight muscles developed. Using ovarian dissection to estimate the ages of nulliparous adult females of G.pallidipes, the Trdw was also found to increase linearly for at least 14 days in the field. Significant increases in pteridine fluorescence with age were measured in both laboratory‐reared males and females of known chronological age and in wild‐caught nulliparous females whose ages were estimated by ovarian dissection. A linear relationship existed between pteridine fluorescence and wing fray category for a wide range of ages of field‐caught flies of both sexes. A stationary trap baited with ox odour was selective in that only the hungrier portion of the flies attracted to it actually entered. However, it was not selective in terms of the mean ages of flies caught. Comparisons were made of the age compositions of catches of both sexes of G.pallidipes attracted to a stationary trap baited with synthetic odours or to a mobile electrified net by plotting Trdw values against pteridine fluorescence. Nulliparous females were not attracted to the stationary trap, but were attracted to the mobile bait. Males of all ages appeared to be equally attracted to both. It is concluded that nulliparous females do not respond to host odour stimuli until they are ready to mate, perhaps relying on the energy‐conserving strategy of watching for a moving host animal before attempting to feed. Alternatively, synthetic odours may differ from natural host odours in terms of their attractiveness to young females. Males, however, probably exhibit dual sexual and feeding behaviour by responding to an odour‐baited stationary trap even when young.

Hormonal control of lipid synthesis in the fat body of the adult female tsetse fly, Glossina morsitans

Abstract Aqueous extracts of brain, thoracic ganglion or corpora cardiaca of female Glossina morsitans were shown to contain a substance which inhibited the synthesis of lipid from l [U- 14 C] leucine by fat cells incubated in vitro . The highest concentration of this substance was found in the corpora cardiaca; approximately 1 × 10 −6 gland pairs μl −1 were required for maximum inhibition. At concentrations greater than 1 × 10 −4 gland pairs μl −1 the lipid synthesis inhibiting factor (hereafter referred to as the LSIF) was inactivated by the presence of a substance which could be removed by gel filtration. The concentration of LSIF in the corpora cardiaca and midbrain varied throughout the reproductive cycle of the female. Net release of LSIF from the midbrain occurred between the 2nd and 7th day of the 9-day reproductive cycle. Net release from the corpora cardiaca began on day 5 and continued until the end of the interlarval period on day 9. Results are consistent with the hypothesis that LSIF is synthesised mainly in the medial neurosecretory cells of the midbrain whereas the corpora cardiaca are the site of storage and release into the haemolymph. LSIF was present in midbrain and corpora cardiaca extracts from male G. morsitans but at lower concentrations than in females. No variation in LSIF concentration could be correlated with the feeding cycle. LSIF activity was not detected in fresh haemolymph but was found at high concentration in boiled haemolymph, suggesting the presence of an inhibitor which was inactivated at high temperature. Preliminary investigations into the nature of LSIF have shown it to be inactivated by proteolytic enzymes and to be recoverable in a single peak from a Sephadex G15 column. Results support the view that LSIF is a peptide hormone which, in conjunction with an inhibitor, controls the lipid synthetic ability of the fat cells of the adult female tsetse fly throughout the reproductive cycle.