Plant mediated effects on parasitoid efficacy in a banker plant system

Project Overview

Project Type: Graduate Student
Funds awarded in 2011: $9,930.00
Projected End Date: 12/31/2013
Region: Southern
State: North Carolina
Major Professor:
Dr. Steven Frank
North Carolina State University

Annual Reports


  • Additional Plants: ornamentals


  • Crop Production: biological inoculants
  • Education and Training: extension, focus group, workshop
  • Pest Management: biological control


    Aphids are an important topic of research because they feed on hundreds of ornamental and vegetable plant species reducing their aesthetic and monetary value. In a nationwide survey, growers placed aphids in the top three most important pests of ornamental plants in greenhouses (IR-4 2007). Sadly, current aphid biological control methods rely on mass releases of commercially sold parasitoids (augmentative biocontrol), leading to a greater financial cost in comparison to the pesticide standard (imidacloprid) (Vasquez et al. 2006). Therefore, in order to promote the use of biological control in commercial greenhouse pest management, biological control must be rendered more effective and affordable.


    Ornamental plants are the most valuable crop grown in North Carolina yielding $22,741 per acre (NCDA 2005). In the United States, ornamental plants are the second most valuable crop worth $14.7 billion (UDSA 2002). For this reason, effective and sustainable aphid management is a priority for ornamental growers (IR-4 2007). However, growers are hesitant to implement biological control because current implementation practices, in which growers have to repeatedly purchase and release natural enemies, make it unpredictable and expensive (Vasquez et al. 2006). The purpose of this project is to increase adoption of biological control by improving a banker plant system for aphid management. Banker plant systems consist of a non-crop grain plant that supports the non-pest bird cherry oat aphid (Rhopalosiphum padi). R. padi, in turn, supports the parasitoid wasp Aphidius colemani which also parasitizes pests such as green peach and cotton aphids. Therefore, A. colemani and reproduce and patrol greenhouses even when no pests are present(Frank 2010).
    Unfortunately, there is little scientific data demonstrating how to use banker plants effectively in greenhouse aphid management. Existing research indicates that knowledge of A. colemani preference for different aphid species and banker plant placement in commercial greenhouses would help increase banker plant efficacy (Van Driesche et al. 2009). Plant architecture may also affect A. colemani’s efficiency at suppressing aphid pests. Currently, plant growers use plant growth regulators (PGR) to alter plant aesthetics and crop production timing. However, PGRs reduce intermodal distance and increase lateral branching which makes plants more architecturally complex. This increased complexity may make aphid host detection and parasitism more difficult for A. colemani, reducing parasitoid efficacy and population growth. Thus, more research is needed to investigate PGR effects on herbivore hosts and parasitoid attack rate. In order to optimize banker plant systems, more research is needed to understand what factors hinder or promote A. colemani’s attack rate.
    We propose to improve the banker plant system for green peach aphid management by studying its effectiveness at suppressing aphids on pepper plants. This study system will render us capable of determining A. colemani‘s attack rate with different plant architecture, variation in preference between M. persicae and R. padi and the density of banker plants needed to efficiently control M. persicae infestations in a commercial greenhouse. By determining A. colemani‘s preference and efficiency at suppressing M. persicae, we will be able to increase efficacy and adoption of this sustainable pest management tactic.

    Project objectives:

    The overall goal of this project is to develop a banker plant system using A. colemani as a sustainable, effective, and economical biological control agent for aphids in greenhouses. To achieve this, the specific objectives are to:
    1) Determine the effect of plant architecture on parasitoid attack rate and aphid pest suppression
    Rationale: Currently plant growers utilize PGRs to alter plant aesthetics and growth rate. PGRs alter plant architecture affecting herbivore placement on the plant and consequently parasitoid foraging efficiency. For instance, plants with more compact leaves are likely to provide refuges for the pest aphids. The drop in parasitoid foraging efficiency negatively affects parasitoid population growth as A. colemani cannot reproduce without its aphid host. Because so little is known regarding these topics, more research is needed to investigate PGR impacts on herbivore hosts and parasitoid attack rate.
    1.1) Determine the effect of plant architecture on parasitoid attack rate and parasitoid and aphid development;
    Rationale: This first experiment will be carried out in order to determine the variation in A. colemani’s attack rate as related to the different plant architectures. This experiment is conducted to stimulate an augmentative biocontrol setting where the parasitoids are released right after purchase.
    1.2) Determine how crop-plant architecture affects banker plant efficacy
    Rationale: This second experiment is to test whether or not the banker plant is providing sufficient parasitoids to decrease aphid numbers. When comparing the results from 1.1 to 1.2, we will be able to determine if parasitoids reared on the banker plant are capable of suppressing pest aphid population numbers at the same rate as the ‘simulated’ augmentative biocontrol methods are.
    2) Determine parasitoid preference for and attack rate of pest aphid species compared to BCOA on banker plants.
    Rationale: This experiment will be conducted in the lab to determine if, when given the choice, A. colemani attacks M. persicae more than R. padi. Past studies on A. colemani have demonstrated that the parasitoid exhibits preference for the host aphid on which it was reared (van Emden et al. 2002). Because past studies have shown that A. colemani reared on banker plants do indeed suppress pest aphid populations, this choice experiment will show what percentage of parastoids preferentially forage on the pest aphid versus their non-pest host aphid. The data from this study will also demonstrate the efficacy of a banker plant system in comparison to augmentative control.
    3) Determine the efficiency of aphid banker plant systems in commercial greenhouse production
    Rationale: To this date, the number of banker plants to place in a greenhouse has not been properly established. This experiment will help determine the correct density of banker plants needed within a commercial greenhouse. Banker plant placement and number is important because parasitoids emerging from banker plants must be able to locate and travel to pest aphids on crop plants throughout the greenhouse.

    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.