Developing beneficial insect habitat for greenhouses

IPM LABORATORIES, INC./BAKERS ACRES OF NORTH LANSING (Trial Site 1)

Orius Establishment and Thrips Control

The Habitat Plant Systems served double duty in thrips control by both supporting the reproduction of Orius and attracting thrips into the pots.

Figure 2 (in Appendix, hard copy) shows the weekly counts of the thrips predator adults and immatures, Orius insidiosus, in the Habitat Plant Systems. Any presence of nymphs is evidence of on-site reproduction by Orius. Images 1and 2 (in Appendix, hard copy) show an Orius nymph and an Orius adult which were collected from HPS. We count this kind of establishment of Orius to be a major success, for we must demonstrate residence by Orius before we can hope to demonstrate long-term control. Figure 3 (Appendix, hard copy) depicts the number of Orius found per hour on the HPS in comparison to the numbers found on the herbs sampled throughout the season. Nearly all the Orius detected season-long were found in the Habitat Plant Systems. In a final survey of the Habitat Plant Systems on August 11, 2005, we detected 123 Orius and 321 thrips on 149 flowers (marigold, lantana, and alyssum). The data showed that the average number of Orius detected per habitat pot increased with the number of flowers in the pot (Figure 4, Appendix, hard copy), with the average number of Orius per flower between 0.5 and 1. Since the literature states that Orius kill 5 to 20 thrips per day, an average of 3 thrips per flower in the presence of Orius may not be cause for alarm, especially if the Habitat Plant Systems are more attractive to thrips than the actual greenhouse crop.

Although we were successful at establishing the Orius, we did not count the trial as an unqualified success because the thrips numbers circulating through the greenhouse in late June were quite high and required a treatment of Conserve to reduce the thrips. The Habitat Plant Systems were removed from the greenhouse before treatment and returned after treatment. This method maintained the Orius populations, while removing most of the thrips with no more treatments required that summer. Figure 5 shows the weekly average numbers of thrips found per 6” spike of rosemary throughout the period. This exceeded 4 just prior to the Conserve treatment, and then fell back to below 1 for the rest of the season.

Aphid natural enemies

Aphid parasites and wild aphid natural enemies reproduced so dramatically on the barley banker plants that we never saw large numbers of aphids anywhere on the retail herbs all season. Image 3 shows aphid mummies on a barley leaf from one of the aphid banker plants. Image 4 shows a lantana leaf with both an aphid mummy and a lacewing egg case that is hatched. The curry plants that we selected to observe for aphids at the beginning of the season averaged a maximum of 1 aphid per 3” tip all season (Fig. 6). This is a very low number. Note that the stock plant control (a mature curry plant) had even fewer aphids, but this can be explained by mature plants having less active growth, therefore being less attractive to aphids than the small actively growing cuttings in the retail herbs. The large upsurge in aphid parasite numbers was demonstrated by more than 200 aphid parasites caught per yellow sticky card between May 26 and June 6. (Figure 7, Appendix, hard copy.) Evidence of aphid demise on the herbs could be seen here and there where a few mummies would dot the herbs with no evidence of live aphids in the vicinity. Aphid parasites were observed on patrol for the rest of the season in the trial herb house. In contrast, the parasitic wasp catch on the yellow sticky cards in the control herb greenhouse was almost zero all season.

The grower had reported in November 2004, before the start of the project, that aphids were her biggest problem and whiteflies her second biggest problem in the herb house. Her records showed that in April 2004 and April 2003 she treated with Botanigard for aphids and a few whitefly. Then in July both years, she treated the herbs with Safer’s Soap for aphids. In 2005, the grower still used Botanigard and horticultural oil in early April, just before we installed the beneficials on the Habitat Plant Systems. However, she never felt the need to treat the herb house for aphids or whiteflies in July.

Wild Natural Enemies

The aphid banker plants attracted 4 families of wild aphid predators and maintained aphid parasites season-long. The Habitat Plant Systems attracted significantly more predators than the herbs and very few predators of any kind were detectable on the herbs season- long (Figure 8, Appendix, hard copy). Image 5 shows a lacewing egg on a barley leaf. The adult lacewing probably laid her egg there due to the presence of the banker plant aphids. Image 6 shows a jumping spider from one of the HPS. Jumping spiders were frequently found in the HPS. Image 7 shows a young lady beetle larva from one of the HPS.

Whitefly Natural Enemies

Whitefly natural enemy establishment on the Habitat Plant Systems also occurred because one of the Habitat plants, lantana, is among the most prolific producers of whitefly in the greenhouse. True to form, when it was placed in the Habitat Plant System, it brought its own greenhouse whitefly. Three weekly introductions of the whitefly parasite, Encarsia formosa followed the introduction of these lantana plants into the herb house Habitat Plant Systems. The final Habitat plant survey on August 11 showed no whitefly evidence on the younger leaves of the lantana (Image 8), and frequent parasitized whitefly scales on the older leaves (Image 9). No adult whiteflies were seen on any of the Habitat Plant Systems, although an occasional whitefly could be seen in the greenhouse.

UNIVERSITY OF VERMONT, Entomology Research Laboratory (Trial Site 2) Participants: Margaret Skinner, Michael Brownbridge, Tom Doubleday, and Cheryl Frank.

For this study the University of Vermont chose two research greenhouses: their Best Management Practices greenhouse was the trial site and their Conventional greenhouse was the control. Each greenhouse is 30x50 ft. Their Habitat Plant Systems contained barley, alyssum, English daisy, and lemon gem, hero yellow and antiqua yellow marigolds. UVM used a slightly different strategy from trial site 1, placing Habitat Plant Systems in both the trial and the control greenhouses, and releasing beneficials only in the trial house. Below are some of their observations (see Appendix, hard copy, for entire report):

Beneficials (Orius insidious and Aphidius colemani) were released in the trial greenhouse only. When native (wild) beneficials (Orius, Aphidius, hover flies and others) turned up in the control house they were found on the Habitat Plant Systems.

Total Insect Occurrences: The following beneficial insects were found on the Habitat Plant Systems in UVM’s trial greenhouse: Orius (21 occurrences), Aphidius (172 occurrences) and Encarsia (2 occurrences). Most notable, however, was the appearance of wild hover flies (10 occurrences) on the Habitat Plant Systems despite the house being screened to exclude infiltration by wild insects.

The hover flies were observed hovering around the alyssum.

Thrips presence was higher in the control house than in the trial greenhouse.

Western flower thrips were lower in the trial greenhouse possibly as a result of suppression by beneficial insects within the Habitat Plant Systems.

In the trial greenhouse, barley had the highest overall insect occurrences followed by lemon gem marigolds, alyssum and English daisies.
Lemon gem marigolds may have offered the most pollen of all the Habitat Plant species, which might account for the higher numbers of thrips and Orius observed there.

More insects were found on barley banker plant (part of the Habitat Plant System) primarily due to the inoculation of these plants with the Bird Cherry Aphids that were used to sustain the introduced population of Aphidius within the greenhouse.

There were no insects found on the barley plants in the control house. It appears that barley attracts insects only when it functions as a banker plant (which turns it into an insectary).

Aphidius was the most dominant beneficial presence on the Habitat Plant Systems in the trial greenhouse followed by Orius and wild hover flies.

During the duration of the experiment, routine scouting found Orius on other plants on three occasions where their presence on the bench was in the vicinity of the Habitat Plant Systems overhead.

In the control house, where no beneficials were released, native (wild) Orius and Aphidius were found on the English Daisies and Lemon Gems.
While the Habitat Plant Systems were in the greenhouse the Aphidius population was the highest it had been all year.

Throughout the duration of the experiment, aphid mummies were always present on all the Habitat Plant Systems at a medium to high density.

CORNELL UNIVERSITY, Department of Entomology. (Trial Site 3) Participants: Jan Nyrop, John Sanderson, and Todd Ugine.

Four greenhouses were each filled with eight 10.2 cm pots spaced evenly throughout the 3.7 m2 of available bench space, on two separate occasions (August and December of 2005). A single “Roma” bean was sown in each pot in Pro-Mix BX peat based media. In two of the greenhouses, four additional pots were added, each containing a single marigold plant, Tagetes patula (cultivar Bonanza Bolero), with two flowers; plants were approximately 4 weeks old. Marigolds were placed in the interior corners of the plot of beans (three rows in from each edge). Twelve and sixteen days after the beans were sown, in tests one and two respectively, 80 adult female western flower thrips, Frankliniella occidentalis, were collected from a laboratory colony and were added to the center of each plot of beans. Additionally, two greenhouses, one with and one without marigolds, had twenty commercially produced adult female and four adult male Orius insidiosus added; in test two a second release of Orius at the same application rate was made 10 days after the initial release. Thus, the treatments were 1) beans + thrips, 2) beans + thrips + marigolds, 3) beans + thrips + O. insidiosus and 4) beans +thrips + marigolds + O. insidiosus. O. insidiosus in the house containing marigolds were added directly to the marigold plants; five females and one male/plant. O. insidiosus in the house without marigolds were added to interior corners of the bean plot (three rows in from each edge). Thirty randomly selected bean leaves were collected from each greenhouse weekly and placed into snap-cap vials filled with 70% ethanol. In test two, ten whole bean plants and one marigold plant were removed on the last sample date. Leaf samples and whole plants were returned to the laboratory and the number of immature and adult thrips and O. insidiosus were enumerated.

Inspection of the mean number of thrips in treatments that included marigolds revealed that thrips abundance was 16 % lower and 25 % higher than treatments that did not include marigolds in tests one and two, respectively (Table 3, Appendix, hard copy). Thrips abundance in treatments that included Orius was 50% and 58% lower than treatments that did not include Orius. Orius were recovered in both treatments that included and did not include marigold flowers. At the end of experiment one (week 3), marigold plants to which O. insidiosus were added were tapped onto a single sheet of white paper. Plant tappings recovered four adult and one immature O. insidiosus. In the second test, two adult (each in the thrips + Orius + marigold treatment) and four immature Orius (all in the thrips + Orius treatment) were recovered; one adult in the first and third weeks of sampling and four immature in the third week of sampling, all on bean leaves; additionally one nymph was observed walking on a bean leaf in the second week. Because of the limited amount of data any conclusions should be viewed as preliminary. The lower thrips abundance (54 % lower on average) at the end of each experiment in treatments that included Orius are likely due to the released predators consuming adult female thrips. This would effectively lower the initial thrips population and cause population growth to slow with respect to treatments that did not include Orius.

Recovery of immature Orius was low in all treatments in which Orius were released; a total of four in samples of beans in the absence of marigolds in comparison to the single recovery of a nymph from marigold flowers. The reasons underlying this low rate of recovery are not known. It is possible that marigold pollen may contribute to reproduction of Orius, although reproduction may also have occurred as a function of Orius feeding on thrips, which is supported by finding of immature Orius in the absence of marigolds. Furthermore, the recovery of adult Orius only occurred in houses containing marigolds. The presence of marigold plants in greenhouses seemed to have no effect on thrips populations either in the presence or absence of Orius.

One serious confounding factor in test one was that thrips abundance was not equal among the greenhouses at the start of the experiment. The greenhouse that started with the greatest number of thrips ended with the most thrips. Similarly, the greenhouses that started with the lowest number of thrips ended with the lowest number of thrips. Ideally, as was the case in test two, the starting number of thrips in each greenhouse should be equal to avoid this confounding effect. We assume that because the bean plants were each sown in their respective greenhouses, that thrips colonized the bean plants before we actually inoculated the plants. In test two, all bean plants were sown in the same greenhouse and randomized to their respective treatments the day that thrips and Orius were added. Different rates of thrips colonization from outside the greenhouse in test one are likely the cause for the different numbers of thrips among the treatments. This is supported by the fact that the growth rates among the treatments are almost identical, in all but the thrips + Orius treatment. (Tables 4 and 5, Appendix, hard copy.)