Factors Affecting Puparia Distribution And Mortality In A Natural Population Of Glossina Pallidipes Austen (Diptera: Glossinidae) At Nguruman, Kenya

Abstract

Glossina pallidipes Austen is an important vector of both human and animal trypanosomiasis in Kenya. In an effort to generate information that could be useful for its control, studies were carried out on its ecology to investigate the factors affecting the distribution and mortality of G.pallidipes puparia at Nguruman, Kenya. It was revealed by these studies that natural puparia mortalities were caused by developmental and emergence failures (29.0 %), pupal tissue degeneration (16.1 %), puparia parasitism (4.4 %) and fungal infections (50.5 %). Regression analysis of k-values of each submortality against the total mortality (K) showed that fungal infection was the most significant factor (r= 0.55, P< 0.05) causing puparia mortality in the field. It was also revealed by these studies that submersion of puparia in water for more than 6 hours caused death probably through asphyxiation indicating that water logging or flooding could result in death of tsetse puparia. These studies also showed that puparia parasites of G.pa11idipes comprised of two diptera species of the family Bombyliidae, namely, Exhyalanthrax lugens Lw and E. beckerianus Bezzi. Mortality caused by these parasites was highest ( 35-100 %) during the short rains. When the weights of field collected tsetse puparia were determined , it was found that the mean weight of ecloded puparia of G.pallidipes was 33.30 ± 0.6 mg . Puparia whose weight was less than 28.3 mg were recovered when they had died before eclosion. It was also shown that parasitised puparia could not be distinguished from unparasitised puparia on the basis of weight, although the former puparia on average were lighter than the latter puparia There were also significant ( t= 13.2, P< 0.01) seasonal variations in the mean weight of puparia collected during the dry and rainy season. Puparia collected during the rainy season were heavier ( 34.40 mg;) than those that were collected during the dry season ( 32.80 mg1). It was also revealed by these studies that there was a significant positive correlation ( r= 0.7, P< 0.01) between puparia weight and relative humidity in the previous month. This indicated that relative humidity in the previous month was an important factor that influenced puparia weight probably because it was the vital climatic factor experienced by the parent female flies. These studies also showed that there were differences in the relative abundance and distribution of puparia recovered from different vegetation types. This was probably due to a seasonal shift in larviposition sites from the lowland riverine vegetation to the valley woodland vegetation during the rainy season. Studies were also carried out to determine the effect of adult tsetse suppression control on the abundance and distribution of G.pallidipes puparia. It was revealed that there was a decline in the live puparia number per site in the suppression area which coincided with a decline in the mean catches of adult flies within the area, suggesting that the distribution and abundance of puparia was to a large extent dependent on the distribution and abundance of adult female flies From these studies it was also revealed that the most important predators of G.pallidipes puparia at Nguruman belonged to two families namely, formicidae ( Order: Hymenoptera) and gryllidae ( Order: Orthoptera). The most abundant formicid ants belonged to the genus Pheidole while those of gryllids belonged to the genus Gryllus. It was also revealed that there were seasonal fluctuations in the numbers of formicid ants and gryllids caught in larviposition sites. The predators were most abundant during the short rainy season and during the cold-dry season. Low numbers of the predators were found during the long rainy season probably due to flooding of larviposition sites. Field experiments were also conducted to determine the rates of tsetse puparia predation buried at different densities and soil depths . It was shown that predation of puparia buried at different soil depths varied significantly ( F= 15.7, P< 0.05). Puparia left on the soil surface were the most damaged compared to those buried within the soil. It was also revealed that there was no significant relationship (P> 0.05) between overall predation rate and puparia density, indicating that puparia predation was not a density dependent factor.