Dynamics of predation on Lygus hesperus (Hemiptera: Miridae) in alfalfa trap cropped organic strawberry

Authors: Hagler, James; NIETO, DIEGO - University Of California; Machtley, Scott; Spurgeon, Dale; Hogg, Brian; SWEZEY, SEAN - University Of California

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2018
Publication Date: 8/7/2018
Citation: Hagler, J.R., Nieto, D.J., Machtley, S.A., Spurgeon, D.W., Hogg, B.N., Swezey, S.L. 2018. Dynamics of predation on Lygus hesperus (Hemiptera: Miridae) in alfalfa trap cropped organic strawberry. Journal of Insect Science. 18(4):12. https://doi.org/10.1093/jisesa/iey077.
DOI: https://doi.org/10.1093/jisesa/iey077

Interpretive Summary: Alfalfa can be strategically planted as a trap crop for Lygus bug, the major pest in California’s organic strawberry fields. It is well known that alfalfa attracts both Lygus bugs and a Lygus-specific parasitoid. However, the impact of alfalfa trap-cropped strawberries on the Lygus predator complex is unknown. Researchers at Maricopa, AZ in collaboration with scientists at the University of California, Santa Cruz identified predators of Lygus found in organic strawberry. First, a general predator survey was conducted at an organic strawberry farm to quantify predator abundance and to qualify their feeding activity on Lygus. Eleven of the most abundant predator (insects and spiders) taxa were identified and, by using a Lygus-specific PCR assay, we determined that about 18% of the predators contained Lygus remains in their guts. We then conducted a study to examine alfalfa’s role in conserving the most relevant predators in alfalfa trap-cropped organic strawberries. Specifically, we quantified predator abundance and qualified predator feeding activity (by gut analysis) on Lygus collected in strawberry plots lacking or containing an alfalfa trap crop. Data revealed that some predator taxa, including the numerically dominant predator, minute pirate bug, aggregated in alfalfa trap crops. The gut content analyses revealed that predators collected from the alfalfa trap crop had a significantly higher proportion of their population containing Lygus remains than those collected from nearby rows of strawberries. This finding, when combined with our previous work documenting improved parasitism in alfalfa trap crops by an introduced specialist parasitoid, illustrates how concentrating prey and host densities in trap crops can conserve biological control agents and broadens the utility of trap cropping in organic strawberry production.

Technical Abstract: Alfalfa (Medicago sativa L.) can be strategically planted as a trap crop for Lygus spp. in California’s organic strawberry fields. Alfalfa has been shown to attract both Lygus spp. and, in turn, a Lygus-specific parasitoid, Peristenus relictus (Ruthe). However, the impact of alfalfa trap-cropped strawberries on the Lygus spp. predator complex is unknown. Here we identify key predators of Lygus spp. found in organic strawberry. First, a general survey was conducted at an organic non-trap cropped strawberry farm to quantify predator abundance and to qualitatively assess their feeding activity on Lygus spp. We identified the 11 most abundant predator taxa present and, by using a Lygus-specific PCR assay, determined that about 18% of the insects and spiders contained Lygus spp. remains in their guts. We then conducted a study to examine alfalfa’s role in conserving the most relevant predators in trap-cropped organic strawberries. Specifically, we quantified predator abundance and qualitatively measured predator feeding activity (by gut analysis) on Lygus spp. collected in strawberry plots lacking or containing an alfalfa trap crop. Data revealed that some predator taxa, including the numerically dominant predator, Orius tristicolor (Say), aggregated in alfalfa trap crops. The gut content analyses revealed that predators (insects and spiders) collected from the alfalfa trap crop had a significantly higher proportion of their population containing Lygus spp. remains than those collected from nearby rows of strawberries. These results suggest that alfalfa trap cropping might be a useful tactic for conserving the biological control services of generalist predators in organically grown strawberries in California.