to A fallacis fall to 5:1 in the second-stage blocks. 

 From July to September, the ratio of pest mites to A. 

 fallacis averaged 9:1 in the second-stage blocks 

 versus 14:1 in the first-stage blocks (Table 1). 



In the 4 orchards which did not receive A falla- 

 cis releases (Table 2), the ratio of pest mites to A. 

 fallacis in 1989 averaged 6:1 in second-stage blocks 

 and 13:1 in first-stage blocks in July, August, and 

 September. In 1990, the ratio of pest mites to A. 

 fallacis averaged 7:1 in the second-stage blocks and 

 6:1 in the first-stage blocks in July, August, and 

 September. A fallacis levels were slow to build, 

 however, allowing pest mite levels to reach 38% in 

 second-stage blocks and 33% in first-stage blocks in 

 August. 



Conclusions 



Our results during the three years of this study 

 indicate that release of A fallacis predatory mites 

 cannot be counted on to provide ongoing pest mite 



control. It may be that the particularly cold weather 

 in December of 1989, accompanied by lack of snow 

 cover, adversely affected the overwintering of A. 

 fallacis. Another possibility is that the predatory 

 mites released are not completely resistant to or- 

 ganophosphate pesticides. Yet another possibility is 

 that predatory mites that had built to high numbers 

 in blocks in which they were released in 1989 moved 

 out of these blocks in April and May, 1990, when pest 

 mites were perhaps too few in number to support 

 predators. Whichever, the finding in 1990 that the 

 ratio of pest mites to A fallacis was essentially no 

 different in second-stage IPM blocks where A falla- 

 cis were released in large numbers in 1988 and 1989 

 and in second-stage IPM blocks where A fallacis 

 had never been released, calls into question the 

 value of releasing predatory A fallacis in apple 

 orchards until further research is conducted. 



In 1991, we plan again to release predatory 



Fruit Notes, Winter, 1991 



11 



