Exjobbsförslag från företag

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Förslaget inkom 2004-03-26

Biologiocal control of leaf beetles / Biologisk kontroll av bladbaggar

Willows (Salix spp.) are grown in Sweden as a renewable source of energy. Plantations of willows are attacked by pathogens and insects. The most severe attacks, so far, has come from leaf beetless Chrysomelidae: Coleoptera). Heavy attacks from leaf beetles may reduce biomass production by up to 39%. The abundance of leaf beetles may vary considerably among years but seem to vary independently in individual plantations. There is also variation within plantations. We need to learn more about the causes behind this variation in order to successfully reach the long-term goal of our research: to develop a sustainable protection of coppicing willows against leaf beetle attack by using a combination of plant resistance and management practices that promote natural enemies.

Below we present two possible areas of research within which we believe that there are great possibilities of formulating research projects suitable as examensarbeten. Project I -Willow hairiness Cuttings from willows grown in laboratory have shown to increase number of hairs (trichomes) on newly sprouting leaves, after grazing by adult leaf beetles. This could be a mechanism to protect new leaves from grazing as hairy leaves is considered to deter herbivores. However, so far we lack good indications on how long time after grazing the increased hairyness is expressed, how it affects the leaf beetles and if the response vary under different
environmental conditions. The willows may react to the grazing by adult beetles early in the season in trying to protect their new leaves against the more severe defoliation that occurs later in the season by larvae. The grazing by adult beetles, early in the season, may therefore indicat how severe the grazing may be later in the season. This has so far only been studied on naturally occurring species of willows. It would therefore also be interesting to study if there is a similar response in the willows grown in plantations. Project II - Role of weeds for natural enemies. It has been suggested that one could increase the possibilities for biological control by natural enemies of insect pests by promoting weeds in plantations of commercial crops. We have observed very high abundances of natural enemies (Heteropterans) on stinging nettles (Urtica dioica)growing in willow plantations. However, it is not clear whether these high densities of enemies on nettles result in higher predation on leaf beetle egg and larvae on the willows. It even seems as if different species of predators may behave differently, resulting in nettles acting as a source for one enemy and as a sink for another. The suggestions above are not in the form of pre-designed, ready-to-go projects. The reason for this is that we would like to develop the project from an idea to a detailed plan together with you.


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