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.
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
Objective 1: Determine optimal ‘Black Pearl’ banker plant density by examining Orius dispersal and efficacy at different distances.
Hypothesis: Orius density and efficacy will decline with distance from ‘Black Pearl’ banker plants.
Sticky cards, vacuum sampling, and sentinel pest populations will be used to determine the effective distance of ‘Black Pearl’ banker plants in commercial greenhouses. This experiment will be conducted in 10 xx m plastic hoop houses at Hoffman’s nursery. Two ‘Black Pearl’ banker plants will be placed at one end of each house. Sticky cards will be hung every 3 m from each banker plant to monitor Orius abundance. One hundred Orius will be marked with fluorescent dust and released on each banker plant at 07:00 h. Every 4 hours for 12 hours sticky cards will be inspected to count the number of marked Orius present at each distance from the banker plants. A 1 m2 patch of crop plants will be inspected for Orius at each distance. Monitoring will be repeated once per day for four days. On the last day an insect vacuum will be used to sample a 1 m2 patch of crop at each distance. Samples will be returned to the laboratory to count marked Orius.
Sentinel populations of thrips and aphids on wheat will be used to evaluate pest predation and population growth rate at each distance. Wheat is a grass that can be grown quickly and has the same aphid (Rhopalosiphum padi) and thrips (Frankliniella occidentalis) pests as ornamental grasses. Wheat will be grown 15 cm tall in 4 inch pots. A standard greenhouse tray holds 15 pots in a 3 x 5 arrangement. To estimate aphid predation, three wheat plants with 100 R. padi each will be placed in the center positions of each tray. Thus, three infested plants will be surrounded by 12 clean plants. Clean plants will buffer the crop from infestation.
Thrips predation will be estimated the same way except the center plants will be infested with 100 first instar F. occidentalis. Development time of F. occidentalis is 19 days (25 C). Juveniles do not have wings and thus do not disperse easily. This will protect crop plants and provide a measure of predation with minimal dispersal.
One sentinel aphid and thrips population (tray) will be placed every 6 m. Trays will remain for 5 days after which aphids or thrips will be counted.
Data will be analyzed to determine the distance at which Orius were found at the recommended density of 2/m2 and aphid population growth was negative and thrips abundance was reduced. Twice this distance will be used as the distance between plants in future experiments.
Objective 2: Determine if biological control by Orius is more effective and economical with ‘Black Pearl’ banker plants than with augmentative releases.
The long-term density, efficacy, and cost of Orius released by hand release will be compared to the banker plant system. This set of experiments provide information necessary to optimize efficacy and economics of the ‘Black Pearl’ banker plant system.
Experiments will be conducted in 12 greenhouses at Hoffman’s Nursery. Four greenhouses will be assigned to each of three treatments: no Orius released, augmentative release of Orius, or Orius released with ‘Black Pearl’ banker plants. All houses are xxft2 and will contain flats of ornamental grasses of mixed varieties. Banker plants will be placed in houses assigned to the ‘banker plant’ treatment at a density determined by Objective 1. xx orius (x/m2) will be released into houses assigned to ‘augmentative’ and ‘banker plant’ treatments. The experiment will continue for 6 weeks (~3 Orius generations) and repeated 2 times (blocks) for 8 replicates per treatment.
Hypothesis: ‘Black Pearl’ banker plants will maintain recommended Orius density and reduce pests more effectively and longer than augmentative releases.
To test this hypothesis, all houses will be inspected twice per week to count 1) Orius adults, nymphs, and eggs; and 2) thrips, aphids, and other pests on banker plants and five randomly selected flats (1 x 2 ft.) of crop plants. An insect vacuum will be used to sample 2 randomly selected 1m2 plots in each house.
In addition, sentinel aphid and thrips populations will be used to estimate predation as described in Objective 1. Five sentinel aphid populations (trays) will be placed in each greenhouse during week 1, 3, and 5. Five sentinel thrips populations (trays) will be placed in each house during week 2, 4, 6. Sentinel populations will remain in greenhouses for 5 days after which Orius, aphids, and thrips will be counted. The number of plants infested and damaged by pests will also be counted.
Hypothesis: will Maintain recommended Orius density will be or economical using ‘Black Pearl’ banker plants than augmentative releases.
To test this hypothesis, the cost of augmentative releases and banker plants will be calculated including: Orius, shipping, banker plants, and labor. In addition, the number and value of plants damaged by pests in each treatment will be calculated based on grower thresholds for salability.
Objective 3: Determine the compatibility of biological control with insecticide using augmentative release or banker plants to maintain Orius populations.
Hypothesis: Orius populations will be higher and pest populations will recover slower in the presence of banker plants.
At the end of each six week experiment described above each house will be treated with spinosad to kill aphids and thrips. Before application banker plants and associated Orius will be placed in cages and removed from the houses. After the 12 h reentry interval, banker plants, which still contain Orius adults, nymphs, and eggs, will be replaced in the houses from which they were taken. Sentinel aphid and thrips populations (as above) will be placed in each house to simulate populations that were missed or were resistant. Orius and sentinel pest populations will be monitored for 5 days to determine if banker plants help repopulate greenhouses with Orius and reduce pest resurgence by cleaning up populations that escape insecticide applications.
We have conducted experiments to fulfill Objective 1 and Objective 2 in large commercial greenhouses at Hoffman Nursery. Results of these Objectives indicated that, contrary to laboratory results, banker plants were not supporting Orius in the field. Thus instead of Objective 3 which was contingent upon banker plants actually harboring Orius populations, we conducted research to determine why banker plants were not improving biological control in this system. We found that in this outdoor nursery banker plants were colonized by spiders. Subsequent experiments found that spiders were both scaring Orius off of banker plants and eating Orius that were on banker plants. This information will contribute greatly to our knowledge of when banker plants are appropriate. We also held a field day at the farm on which our research is conducted.
We have made significant progress understanding how banker plants may be implemented successfully. First were discovered that Balck Pearl pepper plants are an excellent food source for Orius insidiosus. Black Pearl pepper flowers increase Orius life span, adult size, survival to adult, and reduce development time. This results in much greater abundance when flowers are present than when they are not. In addition we discovered that contrary to popular belief banker plants did not improve biological control in an open nursery system. This is because the plants were colonized by spiders which we determine scared and consumed the Orius. As such spiders restricted access to banker plants and biological control was equal between augmentative and banker plant houses.
Educational & Outreach Activities
This work has been presented at the Entomological Society of America National and Southeast Branch meetings in 2010 and 2011. In addition, it was presented at the field day held by our grower cooperator and at an extension meeting of nursery and greenhouse growers in Johnston Co. NC. The work was also presented at national grower meetings in San Diego, CA and Baltimore, MD. This work contributed to the Masters thesis of a graduate student and 2 peer-reviewed publications are submitted.
This project is relevant to sustainable agriculture because its overall goal is to optimize the ‘Black Pearl’ banker plant system which will make biological control more effective, economical, and compatible as a pest management strategy. This will reduce reliance on chemical insecticides and their associated risks to non-target organisms and the environment.
We did not conduct an economic analysis. However, the grower cooperators conduct pest control by conventional pesticides in some of their nursery houses and biological control in others and they have found biological control to be an economically viable way to reduce pest abundance and damage. During our research the cooperators did not have economically damaging pest populations in our biological control houses.
There is great potential for adoption of this technology as indicated by invitations to present at national grower meetings. As a result of our research we know banker plants are most suitable for indoor greenhouses rather than outdoor nurseries. This should help growers who are interested in banker plants decide whether their particular circumstances are appropriate.
Areas needing additional study
Although we made significant progress in this system there is still work to be done. Now that we have completed ground work documented the very real benefit of Black Pearl pepper for Orius we have good justification to seek funding and move forward optimizing implementation in greenhouse systems.