Location: Pest Management and Biocontrol Research
Title: Dispersion and movement of the Lygus spp.parasitoid Peristenus relictus (Hymenoptera: Braconidae) in trapcropped organic strawberries Authors
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2013
Publication Date: N/A
Interpretive Summary: Narrow strips of alfalfa (trap crops) planted in strawberry fields can be used to lure a key pest, the lygus bug, away from the high-value strawberries. This management tactic is particularly important in organic strawberries, where conventional insecticides cannot be used for insect control. The aggregation of lygus bugs by the alfalfa trap crop may also present an opportunity to enhance the impact of natural enemies. One such natural enemy is the parasitoid Peristenus relictus, which is an introduced wasp that attacks immature lygus (nymphs). Studies in trap cropped strawberries on the California Central Coast indicated higher populations of both lygus nymphs and Peristenus in the trap crop rows compared with adjacent strawberries. Lygus nymphs in the alfalfa rows were also more likely to be parasitized by Peristenus than were nymphs in the strawberries. The majority (50 to 85%) of adult Peristenus that were marked to detect movement either stayed in the alfalfa trap crop, or returned to the trap crop after dispersing. These findings reflect a phenomenon called spatial density dependence, in which the higher lygus populations in the alfalfa trap crop enhance the activity and effectiveness of their Peristenus parasitoid. Based on these results, the alfalfa trap crop - Peristenus tactic may be further refined to increase the effectiveness of natural enemies of lygus in organic strawberries.
Technical Abstract: Alfalfa trap crops can be used to manage Lygus spp. in organic strawberries on the California Central Coast. The retention of Lygus spp. in alfalfa creates aggregated distributions that provide improved opportunities for biological control by the introduced parasitoid Peristenus relictus (Ruthe). The abundance and distribution of P. relictus between two trap crops separated by 50 strawberry rows was analyzed in 2008 and 2010. Parasitism of Lygus spp. nymphs by P. relictus (measured by larval abundance and % parasitism) was greatest in alfalfa trap crops when compared with strawberry rows. The spatial distribution of nymphs and P. relictus larvae in and between trap crops was significantly correlated and bimodal. The movement of P. relictus adults from a marked alfalfa trap crop into adjacent strawberry rows or trap crops was also studied in 2008 and 2009 using a chicken egg albumin enzyme-linked immunosorbent assay (ELISA) mark-capture technique. In 2008 and 2009, 85% and 49% of protein-marked wasps were captured from central trap crops, indicating that alfalfa trap crops act as host-density-anchors in organic strawberries that allow for spatial density dependence between parasitoid and host.