Resting sites and predation levels of adult glossina Pallidipes Austen at Nguruman, Kenya

Abstract

This study aimed at investigating the resting sites and assessing the amount of predation done on resting adult tsetse flies of the genus Glossina pallidipes Austen. Tsetse flies were trapped in the field using Zimbabwean F3 traps baited with cow urine and acetone. Flies used for nocturnal resting site studies were dusted with flourescent powder and released in the bush at dusk. When it was fully dark, one-hour long searches were then made using long wave ultra-violet light. This was done from August 1986 to May 1987. Daytime resting sites were investigated during the hot dry and long rainy seasons. It involved searching for resting tsetse flies in a large field cage at four different times of the day, namely early in the morning (05.45 to 06.30 h), late in the morning (10.30 to 11.30 h), early afternoon (13.30 to 14.30 h) and late in the afternoon (16.30 to 17.30 h). For each fly observed, its resting substrate and resting height were recorded. Temperature and relative humidity were also measured. Nocturnal resting substrates were leaves, twigs, branches and tree trunks. strong preferences were shown for twigs and small branches during the cool dry, short rainy and hot dry seaSOAS. Leaves were prelerred during the long rains. Mean nocturnal_resting heights were lowest in the cool dry season (1.5 m), -intermediate and equal in the two rainy seasons (1.7 m), and were 'remarkably high-during the hot dry season (2.3m). Branches and tree trunks were used as daytime resting substrates. During the afternoons of the hot dry season, the ground was preferred, while branches were preferred during the wet season at the same times. No tsetse were found on the ground during the wet season. The nocturnal resting substrates were the ones observed in the very early morning search. Diurnal mean resting heights varied greatly during the hot dry season depending on the time of the day. There was a gradual decrease from 2.03 m early in the morning to 1.21 m late in the morning, and eventually to 0.25 m in the early afternoon. During the long rainy season resting heights fluctuated from 1.74 m to 1.38 m to 1.51 m and eventually to 1.34 m during the four times of the day respectively. Generally tsetse rested higher at night than in the daytime. It was 'observed that temperatures above 250c and relative humidity below 40% were apparently responsible for resting low down on thick substrates, and even on the ground. The amount of predation of resting tsetse flies was assessed at three different resting sites namely leaves, branches and tree trunks, and at three different localities. The method adopted was that deyeloped by Rogers (1974). It involved tethering tsetse flies within a 'metre cube' of the resting substrate. The predatory behaviours of vertebrates, mainly birds and 'lizards were watched from a distance while those of invertebrates were done by inspections at experimental sites. Samples of invertebrate predators were preserved in -xvalcohol for species identification later in the laboratory. The amount of predation occurring in the daytime was distinguished from that which occurred at night. The effects of prey density on predation levels was also investigated. Results obtained were normalized by arcsine square root tranformation and then subjected to multivariate analysis of variance. Field observations showed that daytime predators largely included birds, lizards and jumping spiders of the family Salticidae. Ponerine ants were the main nocturnal predators. The level of total predation on the various resting substrates, i.e leaves (44%), branches (47%) and tree trunks (56%) were not significantly different. Vertebrate predation was however much higher on thick substrates than on thin ones (i.e 37% on tree trunks and 17% on leaves). Predation by ants was indifferent Qf the sites. Level of predation in the daytime (54%) was much higher than that at night (43%). Mean levels of prediction at the three locations were 43%, 61% and 52%. These were shown tg Pe significantly different. These results were caused by the existing local differences in the abundance, distribution and movements of tnepredator populations. Vertebrate predation sh9wed direct density dependence at low densities of up to 8 tsetse flies per metre cube of vegetation.