Epsilon Open Archive

Abstract

Global food security is largely dependent on the use of synthetic pesticides for pest control. This extensive reliance on pesticides, however, has promoted widespread loss of insect diversity; thereby jeopardizing the provision of insect ecosystem services like pollination and biological control. For future sustainability, agricultural practices need to shift from pesticide-dependency towards more balanced approaches such as integrated pest management IPM).

Strawberry cultivation is in particular highly pesticide dependent. To protect pollinators, pesticides could be avoided, but reduced pesticide use might promote floral damage by herbivores and lower yields. Indeed, results from this thesis show that in woodland strawberry (Fragaria vesca, L.) floral damage by strawberry leaf beetles (Galerucella spp.) had indirect effects on pollination and direct effects on yield. Pest-damaged flowers yielded smaller fruits, even when pollinated by hand, and were avoided by pollinators. Breeding crop cultivars for pest resistance is a corner stone of IPM and could provide a potential solution to prevent pollination deficits in low-pesticide cultivation.

Crop wild relatives like woodland strawberry are predicted to show high heritable variation in resistance traits useful for crop improvement. Here, wild accessions of woodland strawberry from Sweden were screened for resistance against strawberry leaf beetles. Heritable genetic variation was found for each plant resistance indicator and oviposition was avoided on resistant plant genotypes. Thus wild woodland strawberry can be deemed to offer a promising resource for restoring pest resistance in cultivated strawberry.

However, modifying plant resistance could also affect the herbivore’s natural enemies. Parasitoid performance was in fact strongly affected by herbivore diet source when tested with different wild woodland genotypes. Yet genotype resistance against the parasitoid’s host, the strawberry leaf beetle, did not predict parasitoid survival. Rather, parasitoid survival was explained by plant foliar chemistry, of which levels of carbohydrates appeared to be the most important for parasitism success. These findings underline the need to assess plant-quality effects on biocontrol in plant breeding programs for a synergistic application in
IPM.

Taken together, this work demonstrates that deeper insight into trophic interactions between crop plants, pests, and mutualists (e.g. pollinators and natural enemies) will be crucial in order to design optimal IPM strategies which suppress pests and support mutualists.