Optimizing biological control of greenhouse pests with banker plant systems

Project Overview

Project Type: On-Farm Research
Funds awarded in 2010: $14,959.00
Projected End Date: 12/31/2012
Region: Southern
State: North Carolina
Principal Investigator:

Annual Reports


  • Additional Plants: ornamentals


  • Education and Training: extension, on-farm/ranch research
  • Pest Management: biological control, chemical control, integrated pest management


    Controlled experiments found that black pearl pepper plants increase survival and abundance of the biological control agent Orius insidiosus. In commercial greenhouses, a comparison of thrips biological control by augmentation and by banker plants found that both successfully reduce thrips abundance to levels tolerable by growers. These treatments also reduced spider mite abundance compared to untreated crops. However, banker plants in this system did not improve biological control compared to augmentation alone. We investigated intraguild predation by spiders as a potential mechanism.


    Ornamental plants are the second most valuable crop in the Unites States ($14.7 billion) and a major crop in the South (USDA 2002). Unique to Southern states, tobacco growers often turn to ornamental crops after the tobacco buyout program (Seagraves 2006). Three southern states, Texas, Florida, and North Carolina are in the top five producers of floriculture crops (USDA 2009). Ornamental plants are the most valuable crop in North Carolina and yield an astounding $22,741/ acre (NCDA 2005). The high value of ornamental crops and low tolerance for damage necessitates protection of plants from arthropod pests.
    In a nationwide survey, growers placed thrips and aphids among the top three greenhouse pests of ornamental plants (IR-4 2007). These were also among the top pests ranked by Southern growers (IR-4 2007). Western flower thrips Frankliniella occidentalis, feed on hundreds of ornamental plants reducing their aesthetic and monetary value. Thrips are difficult to control because they feed in crevices of flowers and foliage making it difficult to contact them with insecticides. Thrips reproduce rapidly so small populations not detected by scouting or that escape insecticidean applications quickly rebound to damaging levels. To counter this, insecticide applications are made 8-10 times per season (Loughner et al. 2005). Likewise, aphids damage every ornamental greenhouse crop. Difficulty detecting aphids coupled with rapid population growth leads to considerable damage countered by numerous insecticide applications.
    Insecticide resistance, pesticide regulations, and consumer demand for products grown in a sustainable manner have promoted interest in biological control. Biological control can reduce pest populations and damage in greenhouses to levels comparable with insecticides (Vasquez et al. 2006). Despite this, growers have been slow to adopt biological control as part of their pest management program and biological control is practiced in just 5% of the estimated 741,290 acres of greenhouses worldwide (van Lenteren 2000). Primary factors affecting adoption of biological control in greenhouses are efficacy, economic cost, and compatibility with other management tactics (Van Driesche and Heinz 2004).
    The complexity of successful biological control contributes to its unreliability and expense. Biological control is most successful when natural enemy releases target small, initial pest populations which requires grower commitment to scouting (Lopes et al. 2009). Success is also improved by repeated, preventative releases rather than a single curative release which increases cost and effort (Lopes et al. 2009). If insecticides are used to target a second pest natural enemies will be killed and money wasted. To counter these obstacles growers need biological control techniques that provide long-term, preventative pest suppression while minimizing expense and time commitments.
    The specific problem addressed in this proposal is that adoption of biological control is hindered by effectiveness, economic cost, and compatibility with other management tactics. To address this problem, our goal is to optimize a new biological control technique called a banker plant system (Frank 2009). To reduce insecticide use and associated risks to the environment and non-target organisms growers need biological control tactics that are simple, effective, and economical.
    Banker plant systems offer a solution to problems of effectiveness, economic cost, and compatibility associated with augmentative biological control. Banker plant systems consist of a non-crop plant that provides food for natural enemies in the form of pollen or a non-pest herbivore so natural enemies can survive and reproduce even when no pests are present. Therefore, natural enemies are ‘released’ from banker plants continuously at no expense to growers. By increasing survival and reproduction of natural enemies within the cropping system, banker plant systems are intended to provide preventative, long term, and economical suppression of arthropod pests (Frank 2009).
    Biological control of western flower thrips generally entails releasing the predatory bug, Orius insidiosus (hereafter Orius) which is generally more expensive than insecticides. Therefore, some growers attempt to manage thrips with ‘Black Pearl’ banker plants to support Orius populations. ‘Black Pearl’ pepper plants produce large amounts of pollen which is used as food by Orius. Since Orius successfully reproduce on a diet of pollen, ‘Black Pearl’ banker plants can sustain a reproducing population of Orius to attack pests when they enter the greenhouse. The pepper plants may also act as trap plants by attracting thrips which get eaten when they attempt to feed on the flowers.
    A barrier to adoption of biological control is that growers must manage multiple pests with complementary tactics including insecticides (Van Driesche and Heinz 2004). We address this in two ways. First, Orius is a generalist predator that will consume aphids, mites and other important pests. Therefore, although promoted as a tactic to manage thrips ‘Black Pearl’ banker plants should also suppress aphids. Second, if an insecticide application becomes necessary, banker plants hosting Orius adults, nymphs, and eggs, can be removed from the greenhouse. After a safe interval banker plants can be replaced to repopulate the greenhouse.
    The ‘Black Pearl’ banker plant system targeting thrips with Orius has been developed largely by growers. Articles about this system appear in industry publications such as Greenhouse Management & Production (Wainwright-Evans 2009). This indicates grower interest which will increase adoption of banker plants if they are economical and effective. However, no research has been conducted to improve and demonstrate the efficacy, economics, and compatibility of ‘Black Pearl’ banker plants in commercial greenhouses.

    Project objectives:

    1) Determine optimal ‘Black Pearl’ banker plant density by examining Orius dispersal and efficacy at different distances.

    2) Determine if biological control by Orius is more effective and economical with ‘Black Pearl’ banker plants than with augmentative releases.

    3) Determine the compatibility of biological control with insecticide using augmentative release or banker plants to maintain Orius populations

    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.