High intensity organic production: a new source for an old nuisance pest, the eye gnat Liohippelates collusor (Townsend)

The eye gnat, Liohippelates collusor (Townsend) (Diptera: Chloropidae), can be a very serious nuisance pest in many parts of the U.S., and has recently renewed its ferocity in Southern California. This pest is not a vector of any consequence, but even in small numbers they can be very annoying to humans and animals. Unfortunately, great numbers of eye gnats are being produced from high intensity organic farming, and those farms are in close proximity to urban and suburban developments in Southern California. There are few solutions available to organic farmers that are being compelled to solve the problem for the local communities. Our research project emphasizes the potential solutions including cultural, physical, and chemical controls. A series of trap designs were investigated and an efficient trap was then used to determine the distribution of adult eye gnats in two widely varying communities using a GPS trapping grid. Laboratory studies have indicated that Ecotrol® (rosemary oil 10% and peppermint oil 2%) and Azatin® (azadiractin 3%), two organic chemical control alternatives, are toxic to eye gnat larvae at relatively high rates, and we have tested these products in organic field production. Using baited traps, we have determined the height limits of eye gnat adults in the hopes that physical barriers may be employed between farms and communities. Numerous control alternatives were employed in the community of Jacumba, San Diego County, California in 2009, and the effect of these methods were assessed and compared to the previous year’s data.