Aphids and thrips

The thesis investigates aphids and thrips in cereals - their biology, occurrence, economic damage, migration and control by integrated pest management. Experiments were carried out in all types of cereals in southern Sweden during the period 1978-2003. The main pest problem in these cereals is the aphid Sitobion avenae. It attacks wheat, the most valuable crop and the second in acreage. A crop loss model is presented based on average annual yield loss in field experiments in high yielding varieties. The most serious thrips pests are Limothrips cerealium and L. denticornis. Other thrips such as Haplothrips aculeatus, Stenothrips graminum, Thrips angusticeps and Frankliniella tenuicornis are minor pests not causing serious damage to cereals but occurring practically every year. Yield loss and economic injury levels were estimated for S. avenae, Rhopalosiphum padi, L. denticornis, L. cerealium and S. graminum. Grain quality parameters such as protein content, germination rate and mycotoxin concentrations in crops attacked by aphids and thrips were generally not decreased in a way that affected the price of the product. The compensation ability of cereals against aphids and thrips is considerable, probably because of the high number of tillers and the fact that the pests generally do not directly attack the grains. Warning and forecasting are essential within integrated pest management, and knowledge about the effect of weather on different pests is important, particularly in southern Sweden where several pests are on the northern limit of their geographical range. Weather is particularly important for L. cerealium and S. avenae. Investigations on the spatio-temporal dynamics of thrips in cereal crops during a single year revealed that many thrips species interact with acreage of the different cereals grown. The strong flyers, L. cerealium and L. denticornis, are specialised on cereals and their two generations provide the best possibilities to utilise different crops in the landscape. Populations of grain aphids were kept around a certain number, probably by natural predators, with aphid years followed by low populations, the so-called density dependence. Protection of these natural enemies through reduced application of pesticides in cereals might make the production more sustainable