Last Wednesday (10/21/09), we released our predatory mites into our twospotted spider mite biological control plots at Piedmont Research Station. Two weeks ago, we treated all our buffer plots with miticide and we treated again about 1 hour before releasing the mites. This strategy worked will last year; we were able to maintain populations in our untreated control plots while suppressing populations in our predator release plots without noticeable movement between them. This year our spider mites showed up about a month earlier than last year, so we'll see if this same methodology works for smaller, younger plants that have a lot of growing left to do. The spider mite populations were so high, however, that waiting to release predators would have jeopardized the trial.
We released 20 predators/plot (that's 1/sq ft). This is higher than field rates, but for the sanity of the mite counter (me) 20 is as low as I wanted to go. Each species was released alone in a plot. Last year, we combined some predators (like in this trial) but our main goal this winter is to see which, if any, of the species released remain active in the protected environment of the tunnels over the winter. We know the spider mites do--less than 10% of the twospotted spider mites observed last winter were diapausing at any given time, and eggs were present all winter long in the tunnels.
The three predator species we released are the same as last year, and 2 have been used commercially in field grown strawberries for a while. (All the photos are from UC IPM, I need to get a camera for my microscope...)
Phytoseiulus persimilis (next to a female twospotted spider mite and her eggs) has been used in strawberries pretty extensively. We don't appear to have an established population in NC, but in parts of California, they move into strawberry fields on their own.
Neoseiulus (Amblyseius) californicus has gained in popularity in the last 10 years for use in strawberries. This is likely thanks to work done in Florida and the Pacific Northwest that has demonstrated its ability to reduce spider mite populations alone and in combination with P. persimilis.
Finally, Neoseiulus fallcis were released. These mites occur in North Carolina, and according to Jim Walgenbach (On Wisconsin!) in our department, they are also found in apple orchards feeding on European red mite. The fact that these guys like cool, humid weather best was the basis for including them in this trial, although they are not widely used in strawberries.
All of our mites were from Rincon-Vitova Insectaries. There are several other suppliers as well, but we could get all 3 of the mites used from them, which will hopefully minimize variability. We do our first post release count next week.