Immigration of Lygus spp. (Hemiptera: Miridae) and predaceous natural enemies to trap-cropped organic strawberry

Authors: NIETO, DIEGO - University Of California Santa Cruz; Hagler, James; SWEZEY, SEAN - University Of California Santa Cruz; Machtley, Scott; BRYER, JANET - University Of California Santa Cruz

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2023
Publication Date: 8/28/2023
Citation: Nieto, D.J., Hagler, J.R., Swezey, S.L., Machtley, S.A., Bryer, J.A. 2023. Immigration of Lygus spp. (Hemiptera: Miridae) and predaceous natural enemies to trap-cropped organic strawberry. Environmental Entomology. 52(5):824-831. https://doi.org/10.1093/ee/nvad085.
DOI: https://doi.org/10.1093/ee/nvad085

Interpretive Summary: The lygus bug is the major strawberry pest. However, alfalfa and native weeds are preferred by lygus. As such, intercropping strips of alfalfa (trap cropping) within strawberry production fields and allowing weeds to flower adjacent to the fields can serve as a sink for both lygus and its predaceous natural enemies. ARS scientists at Maricopa, AZ teamed up with University of California scientists to study the population dynamics and dispersal characteristics of lygus and its associated predator complex in strawberry fields embedded with strips of alfalfa and surrounded by weedy vegetation. First, they examined the preference of immigrating lygus on alfalfa trap crops with and without flowers. The lygus population was up to 2.5 times higher in flowering alfalfa. Using a protein marking method, they then studied the movement of lygus and its associated predators from weeds to strawberry fields embedded with alfalfa trap crops. The majority (71%) of protein-marked lygus that emigrated from weeds were recovered from alfalfa rather than strawberry. Moreover, most protein-marked predators immigrated to strawberry, rather than alfalfa. The marked predator-to-lygus ratio found in strawberry was 5:1. Trap cropping effectively reduced the infestation of lygus in strawberries. Converting weedy areas to native perennial plantings could further mitigate the risk of pest migration while conserving beneficial insects.

Technical Abstract: Lygus spp. are polyphagous pests that overwinter in weedy vegetation. In the spring on the central coast of California, Lygus spp. emigrate from weeds into strawberry fields. Subsequent feeding on strawberry flowers causes fruit deformation that precludes sale on the fresh market. Use of alfalfa (Medicago sativa L.) (Fabales: Fabaceae) as a trap crop has been hypothesized to prevent Lygus spp. colonization in strawberries. We first compared the establishment of immigrating Lygus spp. on alfalfa traps crops with and without flowers. Lygus densities were up to 2.5 times higher in flowering alfalfa relative to non-flowering trap crops, thus distinguishing a source of attraction for this pest. We then examined the movement of Lygus spp. and associated predators from weeds to strawberry fields with alfalfa trap crops using a protein mark-capture technique. Insects and spiders were collected from weeds, strawberry, and alfalfa 1 day, 2 days, and ~2 weeks after an albumin protein mark was applied to weeds bordering strawberry fields. For marked Lygus spp. that emigrated from weeds, the majority (71%) of adults were recovered from alfalfa trap crops, however, all nymphs had immigrated to strawberry. Most protein-marked predators immigrated to strawberry, rather than trap crops resulting in a marked predator-to-Lygus spp. ratio of 5:1. Trap cropping effectively reduced the colonization of Lygus adults in strawberry. Converting weedy areas to native perennial plantings could further mitigate the risk of pest migration, while simultaneously conserving beneficial insects.