Manipulating beneficial insect habitat for control of thrips in greenhouses

Project Overview

Project Type: Partnership
Funds awarded in 2007: $4,998.00
Projected End Date: 12/31/2008
Matching Non-Federal Funds: $4,206.00
Region: Northeast
State: New York
Project Leader:
Carol Glenister
IPM Laboratories, Inc.

Annual Reports


  • Fruits: general tree fruits
  • Additional Plants: ornamentals


  • Education and Training: demonstration, on-farm/ranch research, participatory research
  • Natural Resources/Environment: habitat enhancement
  • Pest Management: biological control, integrated pest management

    Proposal abstract:

    A strong and diverse beneficial insect population is necessary to exert pressure on thrips in greenhouses, but spring crops usually do not offer sufficient habitat to sustain such populations. In particular, the predatory bug, Orius insidiosus migrates out of greenhouses that offer no pollen. In 2005, we demonstrated that Habitat Plant Systems composed of marigolds, alyssum, lantana and an aphid banker plant attracts and supports a strong and diverse population of beneficials, including Orius. Continuously blooming plants offered habitat to 3 introduced and more than 5 wild species of beneficials that established and reproduced. But while aphid and whitefly suppression was well-documented, thrips suppression failed even though Orius did reproduce well. We believe that the failure occurred because the thrips population was already too high when we started. In 2006, the Orius were killed off on the habitat pots after we panicked and sprayed the pots to control the high number of thrips that the marigolds were attracting. In retrospect, we have learned that it is likely that the marigolds were serving the function of what we have named Guardian Plants, plants that lure pests from crops so that natural enemies like Orius can kill them. The data from the 2005 trial indicate that the Habitat Plant System functioned in this way when it was not sprayed. In 2007, we will repeat the 2006 Habitat Plant System trial, introducing beneficials in equal numbers to both the habitat-enhanced 30’x100’ herb greenhouse and a control greenhouse containing bedding plants. The systems will be compared via weekly monitoring of pest and beneficial levels on crops and Habitat Plant Systems. Key to grower adoption of this method are its marketing and public relations appeal. Through promotion of their habitat plants, growers can announce they’re green; and can educate customers as to why this matters; and may defray the costs of their pest control.

    Project objectives from proposal:

    We seek support to demonstrate what we call a “Habitat Plant System” as a means of providing a favorable habitat for beneficial insects, including in particular, the thrips predator, Orius insidiosus. This plant system will serve as a sustained source of beneficials for ongoing pest management. The Habitat Plant System includes a grouping of plants -- specifically Marigolds, Alyssum, and Lantana, -- and an aphid-infested banker plant. In 2005 and 2006, we demonstrated that this system provided pollen, nectar and alternate hosts that attracted and supported a beneficial insect complex of Orius, Encarsia, Lacewings, Aphidoletes, aphid parasites and Syrphid flies. In 2007, we propose to fine tune the thrips management system so that thrips are satisfactorily controlled as well.

    Our proposed solution offers multidisciplinary opportunities, touching areas such as pest and beneficials monitoring, marketing, public relations, and education:

    Pest and Beneficials Monitoring: Scouting largely concentrates on the detection and enumeration of plant pests, but necessarily includes detection and counting of beneficials when biological control is in use. In our attempts to assess beneficial populations, we are developing a sense of the kinds of pest/beneficial ratios that predict a stable pest population. Multiple sets of data are essential to developing understanding of Habitat Systems.

    Marketing: We will highlight the sustainability of the Habitat Plant System and its multiple applications by reinforcing the Blooms for Beneficials brand name through radio spots and newspaper ads. Consumer response will be measured through sales.

    Public relations: We will promote habitat plant systems as evidence of Bakers Acres management’s commitment to non-chemical pest control and environmental stewardship.

    Education: The sustainable methods will be presented at a customer workshop at grower meetings throughout the Northeast.

    3. What are Your Project Methods?

    Habitat Plant Systems will be placed only in the 30’ by 100’ commercial herb greenhouse whereas beneficials will be introduced into both the herb and control house. The timetable for this project is one growing season. The herb greenhouse contains about 250 varieties of potted herbs. A bedding plant house will serve as a “control” to track pest and beneficial population development under “conventional” control without the banker plants.

    We will create habitat for beneficial insects on each of the 24 benches in the herb house by placing one Habitat Pot per bench (three plants each of marigold and sweet alyssum, one lantana plant, and one barley plant infested with grain aphids (which do not attack broad-leafed plants) as banker plants for beneficials that attack aphids). To assure the presence of thrips’ natural enemies in this system, marigolds will be inoculated with Orius in early-mid March, one month earlier than in 2005. Supplemental lighting over the habitat plants will assure that the Orius will not enter reproductive diapause.

    Although the “control” house of bedding plants does not provide a direct comparison to the herb house, it is part of the commercial growing facility and aphids, whiteflies, thrips, and spider mites are shared between these greenhouses. Most important however is that neither greenhouse has flowering plants to support beneficials in the early season.

    Evidence of aphid natural enemies (including all stages of Aphidoletes, Syrphid flies, lady beetles, parasitic wasps and lacewings) will also be assessed via Visual Encounter Surveys in both treated and control houses weekly.

    Data collected on pests and natural enemies in both houses at Baker’s Acres will be summarized graphically for each greenhouse. We expect these graphs to show a third year of evidence that beneficials are detectable in enhanced habitat. Effects on pest populations will be gauged over time with the level of suppression inferred by the rate of increase or decrease in comparison to the pests’ potential for increase.

    Statistical Analysis
    In depth observations of 10 habitat pots on predator/prey ratios and thrips increase or decrease will be replicated among Habitat Pots weekly. Although technically, all Habitat Pots will be in a single treatment site precluding replication there, as the season progresses, each pot will eventually become a unique observation site as the Orius and the thrips move around the greenhouse. The “treatments” will be the predator/prey ratios, and thrips increase or decrease will be assessed as the treatment result with weekly replicates.

    The best whole-trial replication that we can create in this practical situation is replication over time at the same site. Observations over the last 2 years has shown that Orius establishes in the HPS treatment but not in the controls where habitat is insufficient. A third year of establishment will confirm this observation over time. 2007 data will also give a second year of data on predator prey ratios.

    Quantitative and natural history-type observations of pest and beneficial numbers have been very instructive and fruitful to date. We will graphically chart the changes in thrips populations from week to week with the ratios of thrips to predators at the onset of the week. We anticipate that Orius will not be detectable in the conventional house, but will be detectable in the Habitat treatment house, like the last 2 years. We also anticipate suppression of the thrips in the herb house, and we are very interested to document predator/prey ratios whatever the scenario.

    Measurement of pest levels
    Arthropods will be scouted in the treated and control houses weekly from mid-March through September. All pests and beneficials will be counted on each of 2 sticky cards in each house. Levels of pests and beneficials will be assessed on 10 habitat pots in the treated house weekly. In the herb house, the key pests targeted with habitat plants will be checked on 10 “indicator ” plants that are known to attract specific pests. For example, thrips will be counted on marigolds and other flowering plants, aphids on the curry and whitefly on the woodsage and the horehound. When plants are small, the counts will be on the entire plant. As the plants grow, leaves in the lower, middle and upper canopy will be sampled, as well as up to 5 flowers per plant.

    Measurement of predator levels
    Predators are difficult to detect because their numbers are naturally lower than pest levels. We have season-long Visual Encounter Surveys of all 24 habitat pots per week from 2005 and 2006. In addition, we added in-depth beat samples and flower inspections on 10 Habitat Pots each week. In 2005, the data were consistent and reasonable, with obvious generation surges and declines and predator nymphs population peaks preceding predator adult peaks. We will continue using this method in 2007 with the addition of predator / prey ratios below.

    Measurement of ratios between predators and prey
    In our 2005 study, we focused on observing establishment of the predators in the greenhouses with and without added habitat. We did presence/absence observations on thrips, and thus did not get any predator/prey ratios until a final survey of the flowers during August. As in 2006 we will also measure the relationship between Orius and thrips by counting the numbers of thrips and Orius weekly in individual beat samples on crop plants in both greenhouses and habitat plants in the habitat house. These numbers were recorded both individually and as ratios of the number of prey per predator per beat sample. We will report these data in terms of thrips per flower, or per stem (where there are no flowers) and predators per flower or stem. I expect these ratios to vary with plant type and season. These ratios will be graphed against time.

    Measurement of chemical usage
    Spray records for the treatment and the control house will be kept and comparisons will be made of the frequency and the kinds of chemicals used in the two houses.

    Measurement of crop impact
    The crop impact will be measured by the staff at Baker’s Acres who will record any plants that are culled because of thrips damage.

    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.