UC Santa Cruz UC Santa Cruz Previously Published Works Title Relative densities of natural enemy and pest insects within California hedgerows. Permalink https://escholarship.org/uc/item/5tb540qn Journal Environmental entomology, 42(4) ISSN 0046-225X Authors Gareau, Tara L Pisani Letourneau, Deborah K Shennan, Carol Publication Date 2013-08-01 DOI 10.1603/en12317 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Relative Densities of Natural Enemy and Pest Insects Within California Hedgerows Author(s): Tara L. Pisani Gareau , Deborah K. Letourneau , and Carol Shennan Source: Environmental Entomology, 42(4):688-702. 2013. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/EN12317 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. COMMUNITY AND ECOSYSTEM ECOLOGY Relative Densities of Natural Enemy and Pest Insects Within California Hedgerows 1 2 2 TARA L. PISANI GAREAU, DEBORAH K. LETOURNEAU, AND CAROL SHENNAN Environ. Entomol. 42(4): 688Ð702 (2013); DOI: http://dx.doi.org/10.1603/EN12317 ABSTRACT Research on hedgerow design for supporting communities of natural enemies for biological control lags behind farmer innovation in California, where assemblages of perennial plant species have been used on crop Þeld margins in the last decade. We compared natural enemy to pest ratios between Þelds with hedgerows and Þelds with weedy margins by sampling beneÞcial insects and key pests of vegetables on sticky cards. We used biweekly vacuum samples to measure the distribution of key insect taxa among native perennial plant species with respect to the timing and intensity of bloom. Sticky cards indicated a trend that Þeld margins with hedgerows support a higher ratio of natural enemies to pests compared with weedy borders. Hedgerow plant species hosted different relative densities of a generally overlapping insect community, and the timing and intensity of bloom only explained a small proportion of the variation in insect abundance at plant species and among hedgerows, with the exception of Orius spp. on Achillea millefolium L. and Baccharis pilularis De Candolle. Indicator Species Analysis showed an afÞnity of parasitic wasps, especially in the super-family Chalcidoidea, for B. pilularis whether or not it was in ßower. A. millefolium was attractive to predatory and herbivorous homopterans; Heteromeles arbutifolia (Lindley) Roemer and B. pilularis to Diabrotica undecimpunctata undecimpunctata Mannerheim; and Rhamnus californica Eschsch to Hemerobiidae. Perennial hedgerows can be designed through species selection to support particular beneÞcial insect taxa, but plant resources beyond ßoral availability may be critical in providing structural refuges, alternative prey, and other attractive qualities that are often overlooked. KEY WORDS hedgerow, conservation biological control, biodiversity, natural enemy, insectary plant Conservation biological control (CBC) aims to in- over others because of the viscosity or ratio of differ- crease the abundance of resident natural enemies of ent sugars in the nectar (Baker and Baker 1986, Koptur insect pests by reducing mortality events and creating 2005), type of pollen (Haslett 1989, Cowgill et al. 1993, habitat that provides pollen, nectar, alternative prey, Tooker et al. 2006, Hogg et al. 2011), or their physical a favorable microclimate, and shelter for overwinter- ability to access and collect these resources from the ing (Ehler 1998, Landis et al. 2000). Annual and semi- ßower (Idris and GraÞus 1995, Koptur 2005, Olson et annual crop systems are particularly challenging en- al. 2005, Sivinski et al. 2011). In practice, ßoral re- vironments for conservation biological control source provisioning for beneÞcial insects in annual because the high frequency and intensity of tillage and crops has relied on planting insectaries of annual ex- pesticide applications disrupt arthropod community otic forbs, such as sweet alyssum (Lobularia maritima development (Ehler and Miller 1978, Letourneau L. Desvaux), buckwheat (Fagopyrum esculentum Mo- 1998) and reduce ßoral resources (Heimpel and Jervis ench), and coriander (Coriandrum sativum L.) (Bag- 2005). Nectar fuels host searching and increases lon- gen and Gurr 1998, Chaney 1998, Colley and Luna gevity and fecundity in female wasps (Idris and 2000, Johanowicz and Mitchell 2000, Spellman et al. GraÞus 1995, Baggen and Gurr 1998, Johanowicz and 2006, Irvin and Hoddle 2007, Lee and Heimpel 2008), Mitchell 2000, Costamanga and Landis 2004, Berndt at intervals in Þelds managed using existing technol- and Wratten 2005), and can shift the sex ratio toward ogy and cultivation practices. Perennial plants in con- females in some parasitoids (Berndt and Wratten trast, require dedicated land, but the permanent veg- 2005). Protein from pollen can increase survivorship etative cover they provide may be suitable for and reproduction of predators (Cowgill et al. 1993). overwintering (Dennis and Fry 1992), has architec- However, natural enemies may prefer some ßowers tural complexity, and provides shelter from agricul- tural disturbance or environmental extremes, as well 1 Corresponding author: Department of Earth and Environmental as alternative prey, nectar, and pollen (Landis et al. Sciences, Boston College, 140 Commonwealth Ave., Chestnut Hill, 2000, Bianchi et al. 2006). Native perennials can also MA 02467 (e-mail: [email protected]). 2 Department of Environmental Studies, University of CaliforniaÐ enhance local biodiversity, be better adapted to the Santa Cruz, 1156 High Street, Santa Cruz, CA 95064. local environment (see Fiedler and Landis 2007, Frank 0046-225X/13/0688Ð0702$04.00/0 ᭧ 2013 Entomological Society of America August 2013 PISANI GAREAU ET AL.: HEDGEROWS AND INSECT NATURAL ENEMY CONSERVATION 689 et al. 2008), allow for early dispersal of natural enemies herbivore pests on Þeld margins with and without into crop Þelds to regulate crop pests, and thus com- hedgerows established by growers in CaliforniaÕs Cen- pensate for disturbances in annual crop areas (Le- tral Coast region, and to compare the insect fauna tourneau 1998). Although hedgerows have a long his- associated with six species of native perennials as well tory in Europe (van Emden 1965, Pollard 1971, as the impact of ßoral resource availability on these Charrier 1997, Burel et al. 1998, Paoletti et al. 1997, associations. Baudry et al. 2000), in the United States they have been screened less than annual plants for CBC habitat Materials and Methods because of the time needed for establishment. In coastal California, where the climate is mild and We conducted this study in 2005 and 2006 at four land prices are high, growers maximize yield by ro- organic vegetable farms with bordering hedgerows in tating two to three short-cycle vegetable crops from the northern region of the Central Coast of California. March through November and when feasible, follow CaliforniaÕs Central Coast has a Mediterranean cli- with a winter cover crop to restore soil fertility and mate with cool, foggy summers along the coast and prevent erosion. In response to the disturbance caused warm summers inland. Most of the rainfall occurs by intensive crop rotation, alternating deep tillage bed between November and April. Two coastal sites in preparation and shallow in-row cultivations to control Watsonville, Santa Cruz County (36Њ 54Ј37Љ N/121Њ weeds with brief periods of bare ground fallow, some 45Ј20Љ W) had mean daily summer temperatures of growers have established native perennial hedgerows 16Ð17ЊC and 584 mm mean annual precipitation (Na- in vegetable, strawberry, and orchard systems as ben- tional Oceanic and Atmospheric Administration eÞcial habitat for insects, but also as windbreaks, for [NOAA] 2000). For two inland sites in San Benito soil conservation, and weed suppression (Bugg et al. County (36Њ 44Ј44Љ N/121Њ 17Ј19Љ W), the temperature 1998, T.L.P.G., unpublished data). Linear hedgerows was 19Ð23ЊC with 432 mm rainfall (NOAA 2000). measuring 3Ð5 m wide and running hundreds of me- Mixed vegetables and lettuce are the top two com- ters along Þeld edges typically contain assemblages of modities produced in both counties, with production 10Ð40 species of native shrubs, small trees, grasses, and Þelds covering over 265 km2 (U.S. Department of forbs (see Earnshaw 2004 for a complete list). Plant Agriculture [USDA] 2007), an increasing proportion species selection has been based on establishing an of which are under organic management (California architecturally complex and primarily native assem- CertiÞed Organic Farmers [CCOF] 2007). Surround-