faculty of pure and applied sciences - The Department of Chemistry ...

ABSTRACTS OF PRESENTATIONS_________________________________________________________________________________O-1 THE DYNAMICS OF TROPICAL INSECT POPULATIONSBrian FreemanDepartment of Life Sciences, MonaThe dynamics of tropical insect populations have not been studied systematically apart from the work donehere and in Trinidad and Tobago by my research group from 1970 to 1995. Work in Africa has largelybeen directed to solving insect vector and plant pest problems. While this is admirable, it does not directlyimpact on the more fundamental subject of understanding of the regulation of insect numbers on a globalscale. A small amount of work has been done in tropical South America by Anthony Raw, one of my exresearchstudents. Our data thus provide the majority of information to be compared with a considerablebody of work published for temperate and Mediterranean zones. I must add that it is vital to carry outpure research in the Tropics as well as in other regions if we are to achieve a balanced understanding ofany worldwide ecological process.For any fundamental knowledge of the regulation of animal numbers (and most of the research in this areahas been on insect populations), certain basic parameters need to be estimated. They are:1. Developmental mortality - the mortality occurring between fertilisation of the egg and the achievementof adulthood. This is commonly believed to be the most influential parameter.2. The percentage of adults which are female. This often deviates significantly from 50%. Males aredeemed to be merely a factor in female fertility and are often numerically written off.3. The percentage of adult females which survives to reproduce. This factor has often been disregarded.The mean fertility of reproducing females. In insects at least, this is often directly related to sizevariation within the species.If all these parameters can be estimated, and often they have not been, the validity of the conclusionsdrawn from the data depends on:1. The size of the sample;2. The duration of the sampling period;3. The spatial comprehensiveness of the sampling, i.e. how many places were looked at;4. The validity of the logic. For a majority of studies only a single locality has been sampled and for aduration of less than 10 generations.My research group has investigated a variety of contrasted insect groups:A. Solitary bees and wasps (18 species). For all species developmental mortality was low (typically 40 -60%) and directly related to the density of the population except in one important case (Trypoxylonpalliditarse in Trinidad) in which this relationship is inverse. Generally, the sex-ratio was slightly biasedtowards the females. Only 15 - 35 % of adult females survived to reproduce. Fertility was low at 6-15eggs /female. These data are similar to those of Raw for Brazil and Watmough for the South AfricanKarroo.19