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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.

journal of insect science

The effects of strawberry cropping practices on the strawberry tortricid (Lepidoptera: Tortricidae), its natural enemies, and the presence of nematodes