title: The effects of strawberry cropping practices on the strawberry tortricid (Lepidoptera: Tortricidae), its natural enemies, and the presence of nematodes.
abstract: Cropping practice can affect pests and natural enemies. A three-year study of the strawberry tortricid, Acleris comariana (Lienig and Zeller) (Lepidoptera: Tortricidae), its parasitoid Copidosoma aretas Walker (Hymenoptera: Encyrtidae), and its entomopathogenic fungi was conducted in seven pairs of organic and conventional farms to test the hypothesis that farming practice (organic versus conventional) will affect the level of pest infestation and will affect the natural enemies. In addition, the number of years with strawberries on the farm, field age, and other factors that may affect pests and their natural enemies were considered. Farms were characterized by their cropping practices, cropping history, and other parameters. Field-collected larvae were laboratory reared to assess mortality from parasitoids and entomopathogenic fungi. In 2010, a survey of nematodes was made to assess the response of an unrelated taxonomic group to cropping practice. 2,743 larvae were collected. Of those, 2,584 were identified as A. comariana. 579 A. comariana were parasitized by C. aretas and 64 A. comariana were parasitized by other parasitoid species. Finally, 28% of the larvae and pupae of A. comariana died from unknown causes. Only two of the field-collected A. comariana larvae were infected by entomopathogenic fungi; one was infected by Isaria sp. and the other by Beauvaria sp. The density of A. comariana was on average four times lower in organic farms, which was significantly lower than in conventional farms. A. comariana was more dominant on conventional farms than on organic farms. The effect of crop age (One, two, or three years) on A. comariana infestation was significant, with higher infestations in older fields. Crop age had no effect on A. comariana infestation in a comparison of first- and second-year fields in 2010. Cropping practice did not lead to significant differences in the level of total parasitism or in C. aretas parasitism; however, C. aretas contributed to a higher proportion of the parasitized larvae on conventional farms than on organic farms. Mortality from unknown causes of A. comariana was higher in organic farms than conventional farms, and unknown mortality was two to seven times higher in second-generation A. comariana than in first generation. Entomopathogenic nematodes were found on three organic farms and one conventional farm. Plant parasitic nematodes were found in more samples from conventional farms than from organic farms. The low density of A. comariana in organic farms exposes the specialist C. aretas to a higher risk of local extinction. In organic farms, where the density of A. comariana is low, other parasitoids may play an important role in controlling A. comariana by supplementing C. aretas. Other tortricid species may serve as alternative hosts for these other parasitoids, contributing to conserving them in the habitat. The higher unknown mortality of larvae from organic fields may be the result of non-consumptive parasitoid or predator effects. This study reports an example of the effects of cropping practice on an insect pest, with similar effects on nematodes. An understanding of the responsible factors could be used to develop more sustainable cropping systems.
authors.affiliation: University of Copenhagen, Department of Plant and Environmental Sciences, Section of Organismal Biology, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark les@plen.ku.dk.
authors.forename: Lene
authors.initials: L
authors.lastname: Sigsgaard
authors.affiliation: University of Copenhagen, Department of Plant and Environmental Sciences, Section of Organismal Biology, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
authors.forename: Cyril
authors.initials: C
authors.lastname: Naulin
authors.affiliation: Bioforsk, Norwegian Institute for Agricultural and Environmental Research, As, Norway.
authors.forename: Solveig
authors.initials: S
authors.lastname: Haukeland
authors.affiliation: Aarhus University, Faculty of Science and Technology, Department of Agroecology, Research Centre Foulum, Blichers Alle 20, Postboks 50, DK-8830 Tjele, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Kristensen
authors.affiliation: Aarhus University, Faculty of Science and Technology, Department of Agroecology, Research Centre Flakkebjerg, DK-4200 Slagelse, Denmark.
authors.forename: Annie
authors.initials: A
authors.lastname: Enkegaard
authors.affiliation: HortiAdvice Scandinavia A/S, Hvidkarvej 29, DK-5250 Odense SV, Denmark.
authors.forename: Nauja Lisa
authors.initials: NL
authors.lastname: Jensen
authors.affiliation: University of Copenhagen, Department of Plant and Environmental Sciences, Section of Organismal Biology, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Eilenberg
mesh_terms: D000818:Animals; D031985:Fragaria / Q000469:parasitology*; D005658:Fungi / Q000502:physiology; D007915:Lepidoptera / Q000382:microbiology / Q000502:physiology*; D009348:Nematoda / Q000502:physiology; D058871:Organic Agriculture; D010572:Pest Control, Biological
keywords: Acleris comariana; Copidosoma aretas; organic farming; parasitoid