Karl Foord - Extension Educator, Horticulture
At a recent conference on high tunnel horticulture we received an update on biological control from Carol Glenister, the president of IPM Laboratories. IPM Laboratories supplies and supports the successful use of healthy beneficial organisms for the biological control of pests.
Photo 4: View of a leaf surface with evidence of parasitoid wasp Encarsia formosa activity
Carol has coined the term "guardian plants" that function in the following ways: 1) are more attractive to the pest species than the crop being grown i.e. 'indicator' or 'trap' plants, 2) provide forage for natural enemies of the pests i.e. 'habitat' plants, and 3) provide forage for non-pest prey species that serve as an additional food source for natural enemies or serves as a reproductive site for natural enemies i.e. 'banker' plants.
The indicator plants let you know the pest is present and the habitat and banker plants provide resources that encourage the natural enemies to remain and thrive on site.
In natural populations the predator numbers shadow the prey numbers, but the prey species always reproduce more rapidly so there is often a delay in control. If the control comes after the prey has damaged our plants then the predator hasn't benefited our production system. If the two-spotted spider mites are finally controlled by the predatory mites but your tomatoes performed poorly during the battle, there is little cause for celebration. The key is to have predator numbers in sufficient quantity early in development to keep prey damage below an acceptable threshold.
This means knowing what pest you expect to encounter, placing the proper indicator plants, monitoring for pest activity, getting predator species in a timely fashion, providing habitat plants and tracking pest and prey activity and numbers.
Natural enemies such as the following are presently being used to control whiteflies in greenhouses; two parasitoid wasps (Encarsia formosa Photos 1 - 4, and Eretmocerus eremicus Photo 5), and a small lady bird beetle (Delphastus catalinae) Photo 6. Note the incredibly small size of these insects - less than 1 mm in length.
In one experiment Lantana was used as a guardian plant among herbs such as oregano and lemon verbena, and the Encarsia formosa wasp was used as the prey species. The ratio of whitefly pests found on Lantana to those on the herbs was 79 to 1. The whitefly pest was drawn to the trap plant where it met its demise at the "hands" of the Encarsia wasp. This experiment can be viewed in greater detail at http://www.ipmlabs.com/whitefly-predators/plant-pests/whiteflies/biological-controls/
There is a great deal of research being conducted in this area, especially on the functioning of these bio-control organisms in outdoor environs. Consider the number of organisms functioning as parasitoids, predators, and pathogens as noted in Tables 1 - 3.
This is a fascinating research arena and one worth tracking advancements.