Quantitative Sampling Method for Fungus Gnat (Diptera: Sciaridae) Eggs in Soilless Growing Media

Abstract

A simple method is described for separating fungus gnat eggs from soilless growing media. The flotation/extraction method primarily involves the use of a MgSO4 solution (density 1.065 g cm(-3)) and a series of sieving procedures. Bradysia sp. nr. coprophila Lintner eggs were collected in an isolation chamber containing adult fungus gnats. Three soilless growing media were used: Metro-Mix 560 with Scott's Coir, Sunshine LC1 Mix, and Universal SB 300 Mix. Each growing medium was inoculated with 100 fungus gnat eggs. Growing medium samples were processed using separatory funnels and a MgSO4 solution. Eggs were washed through a 250-microm sieve and collected on a 53-microm sieve, and then the eggs were rinsed into glass petri dishes. The sieving process separated fungus gnat eggs from the larger growing medium particulates (perlite, bark, and peat), providing a sample consisting of water, eggs, and fine growing medium particulates (peat). Using a vortex for 60 s increased the number of fungus gnat eggs recovered (37.4 +/- 3.7-67.1 +/- 1.9 [mean +/- SEM]) for all three growing media. The mean number of fungus gnat eggs recovered from the three soilless growing media was significantly different, with the growing medium containing coir (Metro-Mix 560) having the highest recovery rate of 61.0 +/- 2.1. For all three growing media, there was > 50% recovery of fungus gnat eggs. In addition to fungus gnat eggs, this method also may prove useful for quantitative recovery of shore fly (Scatella sp.) eggs and the eggs of other arthropods from soilless growing media.