The attractiveness of cattle urine to Glossina morsitans morsitans Westwood and G. pallidipes Austen was shown to be entirely attributable to the phenolic components which it contains. Four of the eight naturally occurring phenol derivatives (3- and 4-methylphenol, 3-ethylphenol and 3-n-propylphenol) were electroantennographically active, induced upwind flight in wind-tunnel bioassays and increased trap catches in field tests in Zimbabwe. One of the minor components, 2-methoxyphenol, had little antennographic activity but induced upwind flight in the wind-tunnel and appeared to be repellent in field tests.

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The larva of the tsetse fly is nourished by a maternal secretion rich in lipoid (Hoffmann, 1954) and at the time of deposition it contains extensive reserves of chloroform-soluble substances, which will henceforth be referred to as fat. This fat constitutes the sole source of energy during pupal development (Bursell, 1958) and that which remains at the end of development makes up the greater proportion of the food reserves available to the fly prior to its first blood-meal. It is clear that any factor which affects the amount of fat consumed during development will influence the length of life of the newly emerged fly and hence its chance of obtaining a blood-meal. Temperature could be such a factor and, to estimate the magnitude of the effect, the fat content of newly emerged flies was determined following development at different temperatures. Material and methods.Most of the experimental work was done with puparia t of Glossina morsitans Westw. bred from females maintained in the laboratory. Puparia were recovered from the breeding tubes and weighed less than 10 hours after larviposition; they were kept in incubators at the stated temperatures until the flies emerged. The normal rhythm of emergence (Bursell, 1959a) appears to be abolished when puparia are kept at constant temperature, the flies emerging indifferently at all hours. The incubators were inspected at regular intervals from early morning till about 2200 hr., so that during this period flies were recovered soon after emergence. They were kept under observation at about 25°C. until they had reached the stage of being capable of flight and were then killed with potassium cyanide. Of the flies that emerged during the night, only those that were not yet capable of flight at the first inspection were included for analysis.After the flies had been killed, fat content and non-fatty dry weight (referred to as residual dry weight) were estimated by methods described elsewhere (Bursell, 1959a). Eegressions of fat contents on residual dry weight were calculated and samples compared at specified levels of this measure of size. As will be shown below, the relation between size and fat content is not rectilinear over the whole range of size, but within the restricted ranges over which regressions were calculated this departure from rectilinearity was not statistically demonstrable, and failure to take account of it is unlikely to affect the conclusions drawn.In attempting to relate present findings to the biology of tsetse flies under natural conditions it will be assumed that normal shade temperatures give a * Now at Department of Zoology, University College of Rhodesia and Nyasaland, Salisbury, Southern Ehodesia.t To avoid continual circumlocution, the word " puparium " will be used to denote the pupa-rial shell and its contents, whether these comprise a third-or fourth-instar larva, a pupa or pharate adult.

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The direction of flight in tsetse flies (Glossina pallidipes Aust. and G.m.morsitans Westw.) taking off in the presence of certain wind-borne odours showed a significant upwind shift both in the field and in the laboratory. The average angular deviation between the resting orientation and flight direction was not materially affected by odour, but turns were steered in relation t o wind direction if odour was present. Upwind flight in an odour plume was regularly preceded by a standing turn, the fly turning partly or completely into the wind before taking off in upwind flight. This suggests that wind direction was assessed, and flight direction determined, before the fly took off.

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