| Cephus cinctus Norton has been a major pest of spring wheat in the southern prairies of Canada and the adjoining parts of the United States for several decades and the grain yield loss caused by mining of the wheat stem sawfly larva can be severe. So far, major advances have been made to protect crops from this pest. An integrated pest management (IPM) approach has been developed using top-down control, i.e biological control, and bottom-up control i.e. plant resistance and cultural measures. This IPM package has provided the necessary tools to reduce the damage of the wheat stem sawfly and prevent economic losses.Our objectives were to provide some scientific bases for controlling C. cinctus by IPM with following study: to determine the fields and spatial distribution of C. cinctus and its parasitoid Bracon cephi, to test the some agronomic operations effected on C. cinctus and B. cephi, B. cephi effected on fitness of the wheat, the novel genotype effected on C. cinctus and B. cephi, the size of C. cinctus larvae effected on the host selection by B. cephi. The main results of this study as followed:1. To determine the distribution and damage by C. cinctus and compare damage between solid-stemmed and hollow-stemmed wheat and to confirm the population dynamics of its parasitoid B. cephi in Alberta, a field survey was conducted. The results indicated that the solid stem reduced girdling damage by C. cinctus. However, due to lower grain yield of some of the resistant wheat cultivars compared with the hollow-stemmed wheat, some producers did not prefer to choose the solid-stemmed variety. Within 49°02.805' N~49°40.153' N, the increase in latitude had no negative effect on activities of C. cinctus and B. cephi. Although the distribution of C. cinctus showed an'Edge Effect', the difference was not significant within a short distance.2. C. cinctus prefered to lay its eggs into thicker stems of the wheat due to low seeding rate and better growth; the treatment harrowed had neither effect on the emergence of C. cinctus and B. cephi; either lower wheat straw remained or wheat straw choped had negative effect on emergence of B. cephi but had no effect on C. cinctus as harvesting.3. There was no consistent yield benefit and enhanced plant fitness attributed to the C. cinctus parasitoids B. cephi that attack larva at an advanced stage. The wheat stems infested by C. cinctus had a higher yield potential than un-infested stems. Under severe infestation by C. cinctus, the potential positive impact of B. cephi on plant was not sufficient to counteract the damage already caused by C. cinctus larva. Nevertheless, the most severe form of loss from C. cinctus comes from the stems that are girdled and topple to the ground and are not harvested. Therefore, the parasitoids B. cephi significantly reduce the girdling rate and wheat stem lodging during growing season, and still control effectively populations of C. cinctus in following years.4. Our study indicated that wheat genotype had consistent effect on C. cinctus. Novel genotype decreased the survival of C. cinctus and its population in following years. Novel experimental synthetic hexaploid wheat lines G9608B1-L12J11BF02 displayed low levels of infestation and girdling damage. The solid trait of wheat stem had no negative influence on B. cephi directly. However, due to the solid trait effect on infestation and survival of C. cinctus, and the resulting shortage of host larvae, the population density of the B. cephi would decrease in subsequent years.5. The size of C. cinctus larvae had effect on the host selection by B. cephi. This was determined by comparing the surface area and diameter of the image of C. cinctus head capsule between un-parasitized and larvae parasitized by B. cephi. The results showed that the outside diameter of wheat had no effect on the selection of B. cephi. B. cephi preferred larger C. cinctus larva to lay its eggs.
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