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Figure 1 . Average and maximum European red mite densities in 1 998 in plots where T. pyri were released 

 in 1996 and in control plots where T. pyri were not released 



throughout the northeast. Possible abiotic limits 

 are winter cold, summer heat, and low moisture 

 during the summer. However, a review of historic 

 climatic data raises no red flags. T. pyri aggregate 

 in flowers in the spring to feed on pollen. 

 Therefore, to collect predators for release, we 

 collected flower clusters from an orchard at the 

 Experiment Station and shipped these clusters 

 with predators within to cooperators who then 

 affixed the clusters to recipient trees. Each release 

 site consisted of a plot of six trees into which the 

 predators were placed and a plot of six control 

 trees. In early July we also shipped leaves with 

 predators on them from the same orchard. These 

 leaves were affixed to the target trees. To measure 

 the effectiveness of the releases, leaves were 

 collected from the release and control sites and 

 shipped to Geneva. There, predators were 

 collected from the leaves and identified. In 1996 

 releases were made at 40 locations. 



In 1996 T. pyrt were recovered from 38 of the 

 release plots and 16 control plots. In 1997 these 

 numbers had changed to 36 and 19. In 1997, 

 releases were made at two additional sites. In 

 1998, T. pyn were recovered from 38 of 38 release 

 plots and from 33 of 38 control plots! The number 

 of control sites where T. pyri were found was 



surprising. In both 1996 and 1997 the average 

 number of T. pyri in the control plots was more 

 than 10-fold lower than in the release plots. In 

 1998, this difference had to changed to only two- 

 fold lower in the control plots. These results 

 indicate that T. pyri can persist throughout the 

 northeast and are likely indigenous. 



Of course the most important question is 

 whether these predators had any impact on ERM 

 numbers. Shown in Figure 1 are the average and 

 maximum ERM densities in the control and 

 release plots 1998. The average density is the 

 average over the sampling period which generally 

 ran from late May to mid August. The size of the 

 symbols in these figures represent average T. pyri 

 densities and data points with a cross hatch 

 represent sites where we predicted biological 

 control would occur. These predictions were 

 based on T. pyn and ERM densities in 1997. 

 Where biological control was predicted to occur, 

 no oil or ovicide was applied in 1998 for ERM 

 control in the release plots. The dashed lines in the 

 two graphs indicate where the data points should 

 lie if there were no differences between ERM 

 densities in control and release plots. European 

 red mite were generally much more abundant in 

 the control plots than in the release plots. Of the 



Fruit Notes, Volume 64 (Number 1), Winter, 1999 



