1997-1999 reported in the 2000 issue of Fruit Notes 

 suggested that increasing abundance of T. pyri was 

 correlated with decreasing abundance of A. fallacis. 

 This pattern has been observed elsewhere and occurs 

 because establishment of T. pyri usually leads to low 

 levels of European red mites. A. fallacis are only 

 abundant in apple trees when there is a ready supply 

 of pest mites for food. In this study, nearly all the 

 orchards had populations of T. pyri prior to their release 

 in 2000. Therefore, we would expect low numbers of 

 A fallacis. Our resuls are in accord with this 

 expectation. As shown in Fig. 4, data for 2001, 2002 

 and 2003 averaged across all 12 orchard blocks indicate 

 that overall, T. pyri was about ten times more abundant 

 than A. fallacis on sampled leaves. Another way of 

 looking at this relationship is to compare the 

 proportions of T. pyri and A. fallacis found in each 

 orchard (Fig. 5A). In 2001 A. fallacis were found in 

 only four orchards and these were sites where some 

 European red mites were also found. In 2002 there 

 was but one orchard \\ here A. fallacis was collected 

 and in 2003 this number increased to two. Note that in 

 2003 there were four orchards where no phytoseiids 

 were collected and five orchards where no T. pyri were 

 collected. At present, we have no explanation for this. 

 Our final question asked whether establishment and 

 conservation of T. pyri would assure effective 

 biocontrol of European red mites. Previous research 

 has shown that T. pyri. when sufficiently abundant, can 

 keep European red mites at non-damaging densities. 

 Recalll that T. pyri were present in most orchards prior 

 to their release and by 2001, T. pyri were recoverd in 

 all the orchards (Fig. 5A). Shown in Fig. 5B a is the 

 relationship between the maximum density of European 

 red mites observed and the average density of T. pyri . 

 The dashed line was fitted by eye to the data points 

 that reflect the highest European red mite numbers in 

 relation to predator density. This graph shows that 

 when T. pyri numbers are low (< 0.15 per leaf), there 

 is a possibility that European red mite will become 

 problematic. Note that even when T. pyri densities are 

 low, pest mites do not always reach high densities, but 

 the potential is there. On the other hand, when T. pyri 

 were more numerous, European red mites never 

 reached high numbers. It is also helpful to examine 

 changes in the abundance of T. pyri over time because 



our experience has been that once established in an 

 orchard, these predators usually persist in relatively 

 high numbers. As shown in Fig. 5C, this was not the 

 case, as in 2r»03 we did not collect any T. pyri in five 

 of the 12 orchards studied. At present, we can offere 

 no explanation for this decline in predator numbers 



Conclusions 



Across the four years of our study (2000-2003), 

 we gained much useful information on the ecology and 

 biocontrol potential of T. pyri in Massachusetts. Our 

 findings lead us to the following conclusions. First, 

 addition of a substantial amount of cattail pollen (as a 

 food supplerr»ent) to trees in which T. pyri were released 

 in 2000 had no detectable effect on buildup of T. pyri. 

 Thus, there is sufficient alternate food to allow for 

 establishment of T. pyri provided no pesticides harmful 

 to this predator are used. Second, by 2002 T. pyri were 

 equally abundant in plots where they were released or 

 not released, with the exception of two sites where they 

 were only found in plots where they were released, 

 and they were equally abundant among the sampled 

 rows (1, 4, 7). This likely reflects that T. pyri were 

 present in most blocks prior to release. Third, 

 establishment of American hazel trees (known to harbor 

 mite predators) in border areas adjacent to plots of 

 orchard trees did not substantially enhance populations 

 of either T. pyri or A. fallacis in such plots. Fourth, 

 commencing in 200 1 , T. pyri predominated in the study 

 blocks, with A. fallacis absent or at very low levels in 

 most blocks. Only where European red mites were 

 moderately to very abundant were A. fallacis found. 

 Finally, in a majority of orchard blocks T. pyri were 

 sufficiently abundant by 2001 to provide what appeared 

 to be consistently effective biocontrol of European red 

 mites. In some orchard blocks, however, T. pyri did 

 not build to appreciable levels or declined in abundance 

 (for reasons unknown, but apparently not associated 

 with use of offensive pesticides). In some of these 

 blocks in some years, European red mites reached 

 threatening levels. 



Overall, as in our 1 997- 1 999 study, T. pyri showed 

 much promise as an effective biocontrol agent of 

 European red mites in most of the blocks in which it is 

 established and conserved. 



Fruit Notes, Volume 68, Spring, Summer, & Fall, 2003 



11 



