Aloo, Ismail K.2026-03-112026-03-111996-03https://www.suaire.sua.ac.tz/handle/20.500.14820/7378PhD ThesesCinara todocola is a well known pest of Sakhalin-fir (Abies sachalinensis) trees in Hokkaido, Japan. It attacks trees less than 10 years old, and the percentage of infested trees often increase when no winged females exist, indicating that dispersal is done by wingless aphids. The effects of plant spacing, interplanting with non-host plants, shade and direct sunlight on dispersal of C. todocola and their application in forest management was studied. Increased plant spacing, interplanting with non-host plants and direct sunlight prevented/delayed aphid dispersal. However, plant mortality was high since many aphids concentrated on just a few trees. At first each aphid occupied its most suitable position on a plant, and reproduced there. When it become overcrowded some moved to other positions. Such movement occurred suddenly rather than gradually when the population density exceeded a certain level (over 300 individuals per 55cm mean height sapling) under controlled and in open area conditions. This movement, which involved adults and young insects, lead me to speculate that there must be a threshold for mass movement. It is also very difficult to estimate at what colony size aphids begin to disperse, since movement was observed even on a small colony of four. Young aphids tended to stay with their mother, but later they began to move, especially when they reached the 3rd instar stage. Overcrowding, host plant conditions, presence of natural enemies and brushing by dispersing aphids influenced aphid dispersal. Overcrowding of population was avoided by intra- and inter tree movement Temperature influenced dispersal starting time and was earlier at high than low temperatures. During dispersal, when emigrating aphids reached ground level, most turned back and climbed the tree again. C.todocola has a high walking ability compared to tall tree, herbaceous, and agricultural aphid species. The 3rd instar larvae walked longer distance than other stages. It is thus suggested that one of the important functions of this instar is dispersal since no winged female aphids were produced. The 4th instar larvae could not walk long distances because it is thought that, when it reaches this stage it has already started to invest in reproduction and so it will also be too costly for the clones to invest in both dispersal and reproduction at the same stage. Although the proportion of the dispersal investment to body weight was not calculated , it is thought that the ratio is higher in the 3rd instar larvae than other stages. The longer walking distance shown by stem mothers could be due to their lager body size. Higher population growth was observed in June/July and September/October which is related to good food quality in spring and autumn. However, aphids bom in the first generation were larger and heavier than those bom in later generations. Aphid population growth was characterized by : Clumped spatial distribution within some plots, steep and steady population growth, and violent fluctuations in population density. These characteristics may have resulted from combinations of physiological traits intrinsic to the insect and the environment. Population peaks were usually followed by dispersal. Ant attended colonies had higher population growth rates compared to unattended ones. In 1993 and 1994 proportion of trees with aphids attended by ants was 96% and 80%, respectively. As a result, aphid spread was low in 1993 since ant nests restricted their dispersal and encouraged high population growth by protecting them from natural enemies. This lead to the death of 64% of trees infested with aphids in 1993 compared to 42% in 1994. Maximum dispersal distance observed in the field was 16m. Aphids moves randomly, and their walking distance changes with time. When an object is placed in front of an aphid most tended to be a little directional, and they were most attracted to green, followed by yellow colours. They were also attracted to larger rather than smaller objects. It is recommended that a wider plant spacing interplanted with non-host plant species be used to reduce chances of aphid infestation in Sakhalin-fir plantation forest.enCinara speciesTodocola inouyePlant spacingDispersal dynamicsPopulation dynamicsThesis