Does floral farmscaping really improve insect biological control in vegetable systems of the Coastal Plain?

Project Overview

LS09-220
Project Type: Research and Education
Funds awarded in 2009: $165,000.00
Projected End Date: 12/31/2012
Region: Southern
State: Georgia
Principal Investigator:
Peter Hartell
University of Georgia
Co-Investigators:
John Ruberson
University of Georgia

Annual Reports

Commodities

  • Agronomic: buckwheat

Practices

  • Crop Production: biological inoculants
  • Education and Training: on-farm/ranch research
  • Pest Management: biological control

    Abstract:

    Floral farmscaping is the planting of flowering plants in proximity of target crops in order to attract and enhance the populations, fitness, and biological control efficacy of natural enemies. Flowering plants provide food resources such as pollen, floral, and extrafloral nectar for natural enemies. These food resources can be critical for survival and reproduction of natural enemies, and have therefore provided a means of manipulating natural enemies to enhance their biological control efficacy for pest management, in cropping systems. Flowering plants differ in their capacity to supply these food resources; therefore, it is important in designing a farmscaping system to screen potential flower plants to identify and work with those that attract and support desired natural enemies, while excluding those that might compromise the intended goal of pest suppression.

    Predatory arthropods play important roles in natural pest control in agroecosystems. Simplification of modern agroecosystems through monoculture cropping practices has led to decreased abundance, diversity, and impact of these predatory insects. However, due to side effects of chemical insecticides on the environment and human health, natural pest control has grown in emphasis. Abundance, fitness, and biological control efficacy of predatory arthropods can be enhanced by providing them access to non-prey food sources. In the present study, we assessed the suitability of three flower treatments (buckwheat, Fagopyrum esculentum (Moench); a combination of fennel, Foeniculum vulgare (Mill.), and dill, Anethum graveolens (L.); and a combination of sunflower, Helianthus annuus (L.), and yarrow, Achillea millefolium (L.)) for enhancing predator abundance and predation of sentinel eggs of the beet armyworm, Spodoptera exigua (Hübner), in organic broccoli and cucumber systems in Athens and Tifton, Georgia, from 2010 to 2012. There was no evidence for effects of the flower treatments on predator abundance or efficacy. There were few and inconsistent significant differences among treatments in number of sucking predators/plant in cucumber (only Athens in 2011) and total numbers of predators/plant in cucumber (only Athens in 2010). Predation of beet armyworm eggs did not differ among treatments within locations and years. The few significant differences likely reflected random events rather than the effect of treatments, since they were unusual and inconsistent across locations and years.

    We assessed the suitability of three flower treatments (buckwheat, Fagopyrum esculentum (Moench); a combination of fennel, Foeniculum vulgare (Mill.) and dill, Anethum graveolens (L.); and a combination of sunflower, Helianthus annuus (L.) and yarrow, Achillea millefolium (L.)) for enhancing biological control of lepidopteran pests in an organic broccoli production system over three years at two locations. Lepidopteran pest composition varied across years and locations with Plutella xylostella (L.), being the dominant pest in Athens in 2010 and Tifton in 2010 and 2011, while Pieris rapae (L.) was dominant in Athens in 2011 and Tifton in 2012. Diadegma insulare (Cresson) was the dominant parasitoid of P. xylostella in both locations and across the years of the study, while parasitism of P. rapae in Athens in 2011 and in Tifton in 2011 and 2012 was dominated by Tachinids, and by Pteromalus puparum (L.) in Tifton in 2010. There were inconsistent significant differences among treatments, such as in % parasitism of all lepidopteran pupae/plant in Athens in 2011; P. rapae larval density in Tifton in 2011; % parasitism of P. rapae pupae/plant in Athens in 2011; and P. xylostella larva density in Athens in 2011. These significant differences likely reflected random events rather than the effect of treatments, since they were unusual and inconsistent across locations and years.

    We investigated the effects of two flowering plants (buckwheat, Fagopyrum esculentum (Moench) and Indian blanket, Gaillardia pulchella Foug.) on adults of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) parasitoid, Aridelus rufotestaceus (Tobias) (Hymenoptera: Braconidae). We also assessed the suitability of three flower treatments (buckwheat; a combination of fennel, Foeniculum vulgare (Mill.) and dill, Anethum graveolens (L.); and a combination of sunflower, Helianthus annuus (L.) and yarrow, Achillea millefolium (L.)) for enhancing parasitism of lepidopteran pests in an organic broccoli production system, and predation of sentinel eggs of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), in organic broccoli and cucumber systems. Aridelus rufotestaceus lived longer on flowers and 5% honey solution than on water alone. Feeding on Indian blanket and 5% honey solution increased production of mature ova. Apart from few inconsistent significant differences among treatments in the response variables, the flower treatments did not enhance parasitism of lepidopteran pests, as well as predation of S. exigua eggs. The results imply that F. esculentum and G. pulchella can benefit A. rufotestaceus for managing N.viridula. Our results on parasitism of lepidopteran pests and predation of S. exigua eggs might have been confounded by the size of the plots, interactions among predators and available prey, and history of the land.

    The lab experiment with Aridelus rufotestaceus demonstrated the value of flowering plant resources for parasitoids; however, the lab data failed to translate into significant differences for either predation or parasitism in the field. The field studies were dominated by insect pests and natural enemies that have significant mobility, and the small plots used (12×12 meters) may have been too small to allow pests and natural enemies to function independent of the larger landscape. If this is the case, then it would indicate that there is a spatial threshold below which floral farmscaping may be ineffective, and this may have important ramifications for smallholders and limited-land producers, especially if their production system is embedded in a diversified landscape on a larger scale. Limited progress was made on Objective 2 (characterizing the species of natural enemies and pests coming to the flowers and building a database on the species recorded with the intent to develop a field guide). A variety of species were recorded, and these are listed in the text of the report. However, the systematic analyses were not completed as planned.

    Project objectives:

    OBJECTIVE 1: Quantify the impact of floral farmscaping on vegetable pest management, specifically on biological control of arthropod pests by the full suite of naturally occurring enemies in broccoli and cucumbers. We will test several hypotheses to address Objective 1, based on the generally accepted, but unproven, ideas regarding farmscaping:
    (1) Beneficial arthropod abundance and diversity will be greater in plots with floral farmscaping than plots without floral farmscaping, and furthermore, buckwheat will enhance abundance and diversity more than the other farmscape treatments because of its abundant nectar;
    (2) Abundance and diversity of natural enemies will decrease with increasing distance from the central floral resource, and
    (3) Biological control of arthropod pests will be enhanced when flower farmscaping is present in plots, and efficacy will decrease with increasing distance from the center floral resource.

    OBJECTIVE 2: Develop a database of arthropod natural enemies attracted to selected flower candidates for farmscaping in the southeastern United States. We will evaluate a selected suite of flowering plants for the pests and natural enemies they attract for future screenings in farmscape systems. These surveys will form the basis for development of an online field guide to arthropod natural enemies and pests attracted to various flowering plants. The field guide will be initiated with this project, but will require several additional years to complete.

    We will characterize the density, species diversity and richness of pest and beneficial species in the agronomic crop and the farmscape, the rates of predation and parasitism of pests in the agronomic crops, and correlate the yield and quality of the produce with the overall pest abundance and damage. These data will permit us to test the outlined hypotheses, and assess mechanisms underlying the outcomes.

    Unfortunately, limited progress was made on Objective 2 (characterizing the species of natural enemies and pests coming to the flowers and building a database on the species recorded with the intent to develop a field guide). A variety of species were recorded, and these are listed in the text of the report. However, the systematic analyses were not completed as planned.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.