center trees reached 0.4, 0.5, and 0.8 per leaf on 

 small, middle-size, and large trees, respectively. At 

 this time, T. pyri on the two outermost trees of the 

 center row averaged 0.8, 0.1, and 0.3 per leaf on 

 small, middle-size, and large trees, respectively, in- 

 dicating spread of T. pyri up and down the same 

 row in which they were released, particularly in 

 blocks of small trees. There was little or no de- 

 tectable spread of T. pyri onto center trees of the 

 outermost rows of blocks of medium-size and large 

 trees but detectable spread onto such trees in blocks 

 of small trees. In 1998, T. pyri were largely absent 

 or at most present in extremely low numbers in 

 first-level IPM blocks in which they were not re- 

 leased in 1997 (Figure 1). 



As shown in Figure 2, by the latter part of 

 August of 1 998, A. fallacis had built to larger popu- 

 lations in first-level than in third-level IPM blocks 

 of both small and medium-size trees, although the 

 reverse was true in blocks of large trees. In con- 

 trast to T. pyri, which was detectable in third-level 

 blocks of all tree sizes in early July, A. fallacis was 

 not detectable in any blocks (either third- or first- 

 level IPM) until the latter part of July. 



As shown in Figure 3, populations of European 

 red mites in 1998 were barely detectable during 

 July and August in either third- or first-level IPM 

 blocks of small or medium-size trees. They did, 

 however, reach substantial (though not damaging) 

 average numbers in both third- and first-level 

 blocks of large trees. 



Table 1 provides information on the possible 

 influence of both type of pesticide used and abun- 

 dance of European red mites as prey on popula- 

 tion levels of T. pyrt in third-level IPM blocks. It 

 appears that abundance of European red mites had 

 less of an influence on buildup of T. pyri than did 

 type of pesticide used. For example, in Orchard 

 A, latter-August populations of T. pyri in 1998 

 averaged nearly double those of 1997, whereas in 

 Orchard H, latter-August populations in 1998 av- 

 eraged less than one-fourth those of 1997. Latter- 

 August populations of European red mites in 1998 

 averaged the same in both of these orchards. No 

 insecticide harmful to T. pyri was applied in third- 

 level IPM blocks in either Orchard A or Orchard 

 H in 1997 or 1998. In 1997, neither orchard re- 

 ceived any EBDC fungicide or Agri-Mek as a miti- 

 cide. In 1998, Orchard H received three applica- 



tions of EBDC fungicide and one application of 

 Agri-Mek, as opposed to use of only one applica- 

 tion of EBDC fungicide and no Agri-Mek in Or- 

 chard A. These combined data suggest that either 

 the greater number of EBDC applications or the 

 use of Agri-Mek was responsible for the rather 

 sharp decline of T. pyri in 1998 in Orchard H. 



Data from other orchards (Table 1) support the 

 lack of strong influence of abundance of European 

 red mites on extent of T. pyri buildup or decline 

 from 1997 to 1998 (compare Orchard D with 

 Orchard A) and the lack of strong influence of 

 number of applications of EBDC fungicides (com- 

 pare Orchard H with Orchard B, and Orchard E 

 with Orchard A). Instead, it appears that use of 

 Agri-Mek in third-level IPM blocks was the prin- 

 cipal factor responsible for the decline in abun- 

 dance of T. pyri from 1997 to 1998 in third-level 

 blocks in some orchards (compare Orchards D, E, 

 G, and H, all of which experienced a decline by an 

 average amount of about 75% in T.pyn from 1997 

 to 1998 and all of which received Agri-Mek in 

 1998, with Orchards A, B, C, and F, all of which 

 experienced an increase in T. pyri by an average 

 amount of about 240% from 1997 to 1998 and 

 none of which received Agri-Mek in 1998). 



Conclusions 



Combined data from 1997 (reported in the Fall 

 1997 xssutoi Fruit Notes) and 1998 (reported here) 

 indicate that T. pyri mite predators released in 1997 

 became firmly established and proliferated in 1998 

 in those third-level IPM blocks that in 1998 did 

 not receive Agri-Mek as a miticide. Our evidence 

 suggests that abundance of European red mites as 

 prey of T. pyri was a less important factor affect- 

 ing population increases or decreases of T. pyri than 

 was the effect of Agri-Mek per se on T. pyri. Our 

 findings also indicate that by the end of 1998, T. 

 pyri had spread at least as far as three trees up- 

 and down-row from the tree in which it was re- 

 leased in 1997, particularly so in blocks of small 

 (high density) trees where intra-row tree foliage 

 was rather contiguous. Spread to third rows on 

 either side of the row in which T. pyri were re- 

 leased in 1997 was only slight in blocks of small 

 trees and essentially nil in blocks of medium-size 

 and large trees in 1998. 



14 



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



