David A. Dame

Effect of the Chemosterilant Tepa on Glossina morsitans Westw.

Pupae of Glossina morsitans Westw. collected in the Zambezi valley near Kariba, Rhodesia, were brought to the laboratory, and the effects of the chemosterilant tepa were investigated by observations on the resulting adults. In the standard test, 25 pairs of adults were caged together for 28 days at 79°F. and 70 per cent, relative humidity and fed on guinea-pigs, and the survival of both sexes, the numbers of pupae and adults produced and (in some tests) the insemination rate of the parent females were recorded. With untreated flies, the insemination rate was 94 per cent, or more, averages of 28 pupae and 26 adult progeny per cage were produced, and 72 and 77 per cent, of males and females, respectively, survived for the 28 days. These results were compared with those obtained when the flies of one sex in the cage had been treated with tepa either as pupae or as adults. Injection of 1 μg. tepa into the thorax of young males produced complete sterility. Dipping the pupae in 5 per cent, tepa solution for one minute caused complete sterility of adults emerging during the first two post-treatment weeks and partial sterility of males emerging during the third week. Adults emerging from dipped pupae washed one day after treatment were fertile. Dipping pupae in solutions containing 1 or 0·5 per cent, tepa did not completely sterilise the resulting adults. Contact exposure of adult males and females of various known ages usually resulted in complete sterility (99·7%) after exposures ranging from 15 to 240 min. to deposits on glass of 10 or 50 mg./ft. 2 tepa. Males exposed for 240 min. to 10 mg./ft. 2 tepa retained their sterility throughout a 42-day test period and, in special tests, competed well with untreated males for the females, but their life length was reduced by 25 per cent, when unmated and by 33 per cent, when mated. Males exposed for 60 min. or less survived as well over a 42-day test period as untreated males, but those exposed for 15 min. recovered an undesirable degree of fertility. No treatment affected the ability of the male to inseminate the females. Sperm from treated males were motile and appeared normal in their behaviour in the female spermathecae. Dominant lethality induced by tepa was usually expressed during the embroyonic stages, but occasionally was delayed until the pupal stage.

Development of the thoracic muscle and flight behaviour of Glossina morsitans orientalis Vanderplank

Laboratory and field studies were made to study the flight behaviour and development of thoracic musculature in male Glossina morsitans orientalis Vanderplank collected as adults near Kariba, Rhodesia, or emerged from puparia collected there. Muscular development, measured as thoracic residual dry weight, was significantly inhibited by confinement in the laboratory and flight activity declined when laboratory-emerged flies were maintained in the laboratory. Survival of laboratory-emerged flies in the field was only 17% that of field-emerged flies. Irreversible behavioural and physiological inhibition in flight and in flight musculature is therefore believed to occur within the first few hours of adult life as a result of confinement; 70–80% of the confined population was affected. These inhibitions can be avoided by using field-emerged adults for field trials.

Multiple mating of Glossina morsitans Westw. and its potential effect on the sterile male technique.

Virgin females of Glossina morsitans Westw. derived from pupae collected on the field were exposed in the laboratory to virgin sterile males and later to virgin normal males; the resulting productivity was an indication of multiple mating by females. Females inseminated once with sterile sperm and then held for 0, 24 or 96 hr. before being allowed to mate with fertile males produced about equal numbers of progeny 29–56 days later; however, subequal numbers of progeny were produced the first 28 days after the initial mating because of the relationship between the time of the second insemination and ovulation. Females given the opportunity to mate repeatedly for 96 hours with their first mates also mated again with new groups of males, but the incidence of this second mating was lower. Thus, multiple mating of females in the laboratory is established, but its frequency in nature is unkown. When groups of males were exposed to successive new groups of virgin females, the minimum mean number of females inseminated per male renged from 4.9 to 5.6. However, the later inseminations were progressively less effective, and once the complement of sperm of an individual male was depleted, fertility was not recovered. The multiple mating of male and female G. morsitans is not expected to affect the use of sterile males for population control.

Field cage evaluation of the competitiveness of male Glossina morsitans orientalis Vanderplank sterilised with tepa or gamma irradiation

Laboratory and field cage trials were made with male Glossina morsitans orientalis Vanderplank treated with tepa or gamma irradiation to assess the ability of the sterile males to compete with untreated males for normal females when the ratios of treated males to untreated males to untreated females ranged from 4:1:5 to 5:2:5. Irradiation of the pupal and adult stages with 8000 and 15000 rad or 8000 and 12000 rad, respectively, reduced reproduction by 87–100% (mean, 95%). Contact for 60 min on a glass surface coated with 10 mg tepa/ft 2 or exposure to 0·25 ml of 5% tepa in a wind tunnel usually produced complete sterility (mean, 99%) in 0- or 2-day-old male flies. Trials in the laboratory and in a small field cage (288 ft 2 ) with chemosterilised flies generally reduced reproduction to near the expected values. Similar results were obtained with male flies emerging from irradiated puparia, but males treated as adults produced somewhat smaller reductions than expected. Unreplicated competitive trials with chemosterilised and irradiated males in a large field cage (8100 ft 2 ) produced considerably smaller reductions in reproduction than expected, suggesting that treated males released in nature might not compete for normal females as readily as untreated males.