on the trees on which they were released, and this establish- 

 ment was maintained at about the same level during 1998 

 and 1999 (Fig. 1). Higher numbers of T piv; during 1997 in 

 medium and high-density tree plots were probably due to 

 the higher abundance of European red mite prey. There was 

 very little spread of T. pyri in 1997 to the most distant trees 

 up and down the row in which they were released, some up 

 and down row spread (especially in blocks of small trees) 

 by 1 998, and excellent up and down row spread in blocks of 

 all tree sizes by 1999 (Fig. 2). There was no detectable 

 spread whatsoever of T. pyri in 1 997 to the most distant trees 

 across row from which they were released, very slight across- 

 row spread in 1998 (and only in blocks of small trees), and 

 considerable across-row spread m 1 999 (especially in blocks 

 of small trees) (Fig. 3). T. pyri were essentially absent in 

 1997 and 1998 from blocks in which they were not released 

 but were detectable in several such blocks (albeit in very 

 low numbers) by 1 999, suggesting some spread of T pyri by 

 1999 beyond the confines of blocks in which they were re- 

 leased (Figs. 1, 2, 3). 



Data on presence oiA.fallacis mite predators (Figs. 4, 

 5, 6) show a general trend from 1997 to 1998 and 1999 to- 

 ward lesser abundance in blocks where T. pyri were released, 

 compared with blocks where no T. pyri were released. There 

 was no apparent influence of tree size or location of sample 

 site within blocks on abundance of A. fallacis. 



Data on abundance of European red mites (Figs. 7, 8, 

 9) show little suppressive effect of T. pyri in 1997. In 1998, 

 T. pyri strongly suppressed European red mites in the small 

 and medium sized trees into which the predators were re- 

 leased. During the same year there was moderate suppres- 

 sion of European red mites throughout the third-level IPM 



plots of medium and small trees. By 1999 T. pyri strongly 

 suppressed European red mites throughout all the third-level 

 1PM plots. 



Conclusions 



This 3-year study of movement of released T. pyri 

 among trees in blocks of different tree sizes (perhaps the 

 only one of its kind) shows that by the third year after re- 

 lease, T pyri can spread effectively as far as three trees away 

 up and down rows and three trees away across rows, with 

 spread fastest and greatest in blocks of small tree size. Also, 

 by the third year after release, T. pyri is able to very effec- 

 tively suppress pest mites in parts of blocks where it has 

 become firmly established. Our findings argue strongly in 

 favor of releasing T pyri for biocontrol of European red 

 mites in apple orchards and suggest that releases be made 

 no further apart than every sixth tree in high-density plantings 

 or every third tree in low-density plantings for rapid estab- 

 lishment throughout an orchard. 



Ackno n'ledgni ents 



We are grateful to the eight growers participating in 

 this experiment and who made special effort to apply pesti- 

 cide selectively to third-level IPM blocks; Bill Broderick, 

 Dave Chandler, Dave Cheney, Dana Clark, Dave Shearer, 

 Joe Sincuk, Tim Smith, and Mo Tougas. This work was 

 supported by State/Federal IPM funds and a grant from the 

 Northeast Sustainable Agricultural Research and Education 

 Program. 



it it *k it it 



16 



Fruit Notes, Volume 65. 2000 



