Conventionally sprayed trap crops reduce eye gnat Liohippelates collusor (Townsend) populations in organic production

The eye gnat, Liohippelates collusor (Townsend) (Diptera: Chloropidae), can be a very serious nuisance pest in agricultural areas. It is being produced in very great numbers from high intensity organic farming, and those farms are in close proximity to urban and suburban developments in Southern California causing great concern for the public. There are few solutions available to organic farmers that are being compelled to solve the problem for the local communities. In 2008 we suggested several measures to the grower that may help reduce populations that included deep tilling, allowing the post-harvest refuse to dry out prior to tilling and mass adult trapping. The average number of adult gnats caught per trap per day in the community in the October 2008 was 158.4. In 2009 we suggested further measures and applications of an organic pesticide that appeared to have an effect on immatures in the laboratory. In 2009, the number of gnats caught per trap per day in the community averaged 17.6, but the numbers were still not reduced enough to provide relief for the community. During the 2010 production cycle, a trap crop barrier was constructed that included rows of alfalfa that were treated with conventional pesticides. In addition, the farm began mass trapping of adults at the border between the community and the farm. In 2010 the number of gnats caught per trap per day in the community averaged 1.3, and the difference was noticeable by the community.