Dispersion, Distribution, and Movement ofLygusspp. (Hemiptera: Miridae) in Trap-Cropped Organic Strawberries

Abstract

Alfalfa (Medicago sativa L.) is a highly attractive plant host to Lygus spp. and is used as a trap crop in California organic strawberries to influence the dispersion and dispersal of these pests, particularly Lygus hesperus Knight. The abundance and distribution of Lygus spp. nymphs between two trap crops separated by 50 strawberry rows was analyzed in 2008 and 2010. Nymphs demonstrated a bimodal distribution in strawberries between trap crops, where nymphs were most abundant and aggregated in alfalfa, when compared with interior strawberry rows, where nymphs were less abundant. The majority of nymphs were concentrated in trap crops and nymphal densities in interior strawberry rows were well below economic thresholds. The movement of Lygus spp. 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 mark-capture technique. The majority of marked-captured L. hesperus adults and Lygus spp. nymphs remained in alfalfa trap crops, rather than dispersing out into strawberry rows at 24 h, 48 h, and 2 wk, postprotein application. The attenuation of Lygus spp. movement in alfalfa associated with organic strawberries is a key component of successful trap cropping. A small percentage of marked adults and nymphs were captured in neighboring alfalfa trap crops, located 62 m from the point of protein application, highlighting the dispersal capacity of this key pest.

Spatial Density and Movement of theLygusspp. ParasitoidPeristenus relictus(Hymenoptera: Braconidae) in Organic Strawberries With Alfalfa Trap Crops

“…As braconids (particularly females) have exhibited dose-dependent responses to plant or plantÐ host volatile emissions (Eller et al 1988, Vaughn et al 1996, Hoballah et al 2002, the aggregated distribution of Lygus spp. hosts in alfalfa (Swezey et al 2013) may concentrate these chemical cues, thereby enhancing alfalfaÕs attractiveness to P. relictus. It is also possible that the "quality" of these chemical signals, in which the volatiles emitted by alfalfa or damaged alfalfa are superior (i.e., preferred) to comparable cues from strawberry, may also attract P. relictus to Lygus spp.…”

“…A description of the experimental sites used in this study is found in the article by Swezey et al (2013). To determine the distribution of Lygus spp.…”

“…These central marked trap crops, along with adjacent strawberry rows 1, 2, 3, and 10, and neighboring trap crops (50 rows away) on each side of the central marked trap were sampled 1, 2, and 14 d after protein application, as described by Swezey et al (2013). Because of low capture rates, mean abundance of protein-marked P. relictus by plant (alfalfa vs strawberries) was pooled over sample dates within years and was compared using the nonparametric KruskalÐ Wallis test after data would not meet assumptions of normality.…”

“…The consequent attraction and retention of Lygus spp. by alfalfa creates aggregated distributions within trap crops that make removal of these insects via tractormounted vacuum more efÞcient (Swezey et al 2013) and reduce damage in adjacent strawberries (Swezey et al 2007).…”

“…The strawberryÐalfalfa trap crop production system creates a unique opportunity for beneÞcial insects to respond to host/prey spatial concentrations (Swezey et al 2013).…”