Manipulating beneficial insect habitat control of thrips in greenhouses

Manipulating beneficial insect habitat control of thrips in greenhouses

Summary

A strong Orius insidiosus population is necessary to exert pressure on thrips in greenhouses but greenhouse plants usually do not offer sufficient pollen and shelter to sustain these natural enemy populations. As a result, the Orius does not establish in the greenhouse and growers are forced to resort to chemical interventions to protect market-bound plants from thrips damage.
This project sought to demonstrate that a habitat of continuously blooming plants could sustain establishment and reproduction of the thrips predator, Orius insidiosus and thereby maintain thrips populations below the action threshold. Bakers Acres of North Lansing participated in this trial by placing Habitat Plant Systems (HPS) in their herb greenhouse and offering a nearby bedding plant greenhouse to be used as a control.
For the HPS, we selected the same plants that successfully sustained Orius in our 2005 trial: two marigold plants (for pollen and harborage), 2 alyssum plants (for cool season pollen and nectar), 1 lantana (for hot season pollen and nectar) and a barley-cereal aphid banker plant (an aphid natural enemy support). We grouped these plants in hanging baskets called “Habitat Plant Systems” (HPS). We released commercially produced Orius and Aphidius in April May, and June into both the HPS and the control greenhouses. We scouted from March to August, observing and recording the presence of natural enemies (both commercially introduced and wild), and pests in and around the Habitat Plants Systems to determine whether offering habitat was an effective way to attract and sustain populations of beneficial insects.

In 2006, we did not attain our objective of managing the thrips without pesticides. However, we demonstrated for the second year in a row, that Orius would establish where HPS were offered but would not establish where appropriate habitat plants were not offered. We also developed important scouting methodology that we expect to use in future biological control decision-making. Our data show that the HPS counts for thrips on marigolds greatly exceeded the numbers on the crops, and may actually be pulling the thrips away from the crops, an ideal scenario if the natural enemies are in high enough numbers to reduce the thrips in the HPS.

Objectives/Performance Targets

In 2006, two retail greenhouses were selected; Greenhouse 3 to house the Habitat Pot Systems (HPS) and Greenhouse 2 as a control under conventional pest management. Both Greenhouses 2 and 3 are approximately 94 ft. by 28 ft., or 2632 ft2; contain 24 benches, each about 55 ft2; and are temperature controlled. Greenhouse 3 contained about 250 varieties of herbs along with many hanging baskets of petunias and geraniums. Greenhouse 2 houses many different kinds of annuals; impatiens, petunias, lantana, ivy and marigolds being the most common.

Scouting began on March 23,2006 with an overall evaluation of pest populations in the selected greenhouses. Visual inspection of plants, 2 yellow sticky cards per house, and beating of specific plants were the primary methods of evaluation.

The Habitat Plant Systems (HPS) were introduced in Greenhouse 3 during the first week in April and contained 2 Marigolds, 2 Alyssums, 1 Lantana plant, and approximately 10 Barley plants with cereal aphids. The aphids in the barley provided a constant food source for the beneficial insects throughout the summer. The 24 Habitat Pots were hung about 12 inches above each table.

Natural Enemy Population Monitoring
A Visual Encounter Survey was done upon arrival in both greenhouses, with no physical contact made with the HPS. The purpose of the “hands off” approach was to observe and more accurately record the natural enemies before they were scared off. In addition to the Visual Encounter Survey, we randomly selected 10 HPS to be permanent sampling sites for in-depth observations by dividing the house into 6 sections per side, with 2 benches per section, and randomly selecting one bench per section by flipping a coin. When the marigold, lantana and alyssum were big enough, they were beaten 3-5 times onto a white piece of paper and the pests and natural enemies that fell out were counted and placed back into the HPS. The presence/absence of aphids on the barley was also noted.

Pest Population Monitoring
Pest numbers were also counted and noted during the in-depth monitoring of the HPS. This was done to examine the ratio between natural enemies and pests. Indicator plant species were selected in both greenhouses for inspection. These plants were selected based on prior knowledge for pest harborage. For whiteflies, we examined Wood Sage and Bee Balm by randomly selecting and inspecting 4 upper, middle and lower parts of the plant. For aphids, 10 randomly selected Golden Marguerite and Lime Balm plants were beaten 3-5 times onto white paper and pests counted. For thrips monitoring, Rosemary, Petunias, and hanging geraniums were monitored by randomly selecting 10 plants each and beating. Rosemary and geraniums were beaten 3-5 times; Petunias were beaten 5-7 to compensate for the plants being very sticky.

Yellow sticky cards were placed in the eastern and western ends of both greenhouses. Insects were counted and the sticky cards were replaced every week.

Orius/Thrips Ratios
Orius and thrips numbers were counted and recorded per beat sample along with the number of flowers per beat sample and per HPS. all HPS throughout the season and ratios of Orius to thrips per flower were calculated. We recorded the number of minutes for surveys of the HPS and the crops in each greenhouse in order to calculate the numbers of Orius detected per hour and thrips detected per hour.

Accomplishments/Milestones

For the second consecutive year, we have observed the thrips natural enemy, Orius insidiosus, easily in the HPS, and rarely, if at all, in the greenhouse crops. In the conventional control greenhouse, Orius simply did not remain in the greenhouse, whereas this predator was always detectable after it was first introduced in the HPS treatment.

In developing new scouting methodology to support biological control of thrips in greenhouses, we demonstrated a pest/natural enemy evaluation technique that compares the numbers of thrips per Orius in a pest/predator ratio.

We have set a preliminary “action threshold” ratio at 5 thrips per Orius, at which point either more Orius must be added to the system, or a corrective pesticide treatment is necessary.

Impacts and Contributions/Outcomes

1) Establish a thriving population of the thrips natural enemy, Orius insidiosus. Orius established but did not thrive this year. In comparing 2005 with 2006, the major difference in establishment was that in 2005, we began releases of Orius 2 weeks earlier and we did not panic when we observed high numbers of thrips in the HPS, whereas in 2006, with our mandate to control the thrips, we treated the HPS with Botanigard and Azatin when the numbers of thrips in the HPS became alarming. In comparison, in 2005, we treated only the crop for thrips and did not treat the HPS for thrips, even though they harbored many thrips. Although we had intended to begin releasing the Orius in March in 2006, the marigold blooms were not ready until late April.

2) Suppress thrips population increase in the HPS treatment. Based on sticky card counts, the thrips populations were not any better in 2006 than in 2005.

3) Scouting Methodology
a) We have graphed detailed data on the relationship between the number of thrips detected in the HPS with the numbers of thrips found in the various crops. A clear relationship is obvious, with the HPS marigold flowers showing much higher thrips populations than the crop, seemingly pulling the thrips out of the crop. Indeed, even where the thrips numbers spiked on the crop, the next week, the HPS marigolds showed a higher spike, which leads us to suspect that the thrips were migrating from the crop to the HPS marigolds.

b) We monitored the natural enemy populations season-long in the HPS. The natural enemy, Orius, was most abundant in the HPS, except on one crop plant that had a spider mite outbreak. With this exception, Orius was barely detectable in the crop, but nearly always detectable in the HPS.
c). We documented thrips/Orius ratios season-long to develop an idea of acceptable thrips/Orius ratios. With the exception of the first two weeks after the first release of the Orius, the thrips/Orius ratios were always greater than 5 this season.

4) Develop marketing/public awareness tools. We developed a set of cards for the growers to use to point out ongoing natural control of pests in their greenhouses.

5) Reports via presentations and media.
Outreach efforts in 2006 included presentations to greenhouse growers New England and North Carolina, pending presentations in California in February and Mississipi in March, and information exchange with scientists investigating plants that harbor beneficial insects in Europe and Canada. Press releases to Tompkins Sustainable, and area news organizations announced and described the habitat project in the spring. Bakers Acres spring newsletter announced the second year of research and demonstrations of developing habitat for beneficial insects in the greenhouse.

Collaborators: