Manipulating beneficial insect habitat for control of thrips in greenhouses
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 such 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 2007, we did not attain our objective of managing the thrips without pesticides. By improperly forcing early flowering of the marigolds, we induced weak root systems which did not compete well in the habitat pot assemblage of plants. This resulted in very few marigold flowers in the greenhouse throughout the season and rare incidence of Orius nymphs in the marigold flowers. The presence of a nymph in a flower indicate that the Orius stopped in the flowers long enough to lay at least one egg. This year, the sweet alyssum was more attractive to the Orius and harbored more Orius nymphs than the marigolds.
Demonstrate successful thrips management by adding habitat for thrips natural enemies to a greenhouse growing herbs and ornamentals. Success will be demonstrated by
1). Establish increasing Orius populations in (Habitat Pot Systems) HPS before the thrips populations begin to increase. Observe and compare establishment of Orius in the control greenhouse without the HPS.
2). Suppress thrips population increase season-long. Based on our experience, we suspect maintenance of thrips/Orius ratios in marigold flowers numbers at or below 5 thrips per Orius may suffice to maintain season long control.
3). Demonstrate scouting methodology using marigolds as trap/indicator plants for beneficials as well as for thrips.
a). Observe the relationship between the number of thrips detected in marigold flowers in the HPS with the numbers of thrips found in the various crops.
b). Use HPS to monitor beneficial populations season-long.
c). Document thrips/Orius ratios season-long.
4). Develop further marketing/public awareness tools for the retail grower to demonstrate their sustainable pest control efforts.
5). Report on research efforts to grower groups via presentations and media.
For the third consecutive year, we have observed the thrips natural enemy, Orius insidiosus, more easily in the HPS, and rarely, if at all, in the greenhouse crops. However, this year, the marigolds established very weakly in the HPS and offered relatively few marigold flowers throughout the season. Although evidence of Orius reproduction was found in the HPS in the sweet alyssum, Orius simply did not establish in the marigolds or remain in the greenhouse in 2007.
In developing new scouting methodology to support biological control of thrips in greenhouses, we tested a pest/natural enemy evaluation technique that compares the numbers of thrips per Orius in a pest/predator ratio. We are still analyzing the data and will report on the outcome in the final report.
Impacts and Contributions/Outcomes
1). Establish a thriving population of the thrips natural enemy, Orius insidiosus. Orius established briefly but did not thrive this year. In comparing 2005, our only successful year for establishing the Orius, in 2007, we simply had few marigold flowers in the HPS. It was interesting to note that
2). Suppress thrips population increase in the HPS treatment. Based on sticky card counts, the thrips populations were not any better in 2007 than in the previous years.
3). Scouting Methodology
a). We have detailed data on the relationship between the number of thrips detected in the HPS with the numbers of thrips found in the various crops.
b). We monitored the natural enemy populations season-long in the HPS. The natural enemy, Orius, was most abundant in the HPS.
c). We documented thrips/Orius ratios season-long.
4). Develop marketing/public awareness tools. We must still develop the web-page for Bakers Acres documenting this project.
5). Reports via presentations and media.
Outreach efforts in 2007 and 2008 included presentations to greenhouse growers in New England, New York State, Oklahoma, Pennsylvania, and Maryland.