which predators and the bean leaves were mixed with 

 cool, damp bran as a spreading medium. The mixture 

 was gently but thoroughly turned by hand before deliv- 

 ery to orchards where it was applied under or upon the 

 canopy of apple trees. Releases were timed to coincide 

 with the time when 20 to 40% of the leaves in the first- 

 stage and second-stage blocks were infested with pest 

 European red mites or two-spotted mites. We rea- 

 soned that releasing predators in a block with too few 

 pest mites (less than about 20% of leaves infested) 

 might stimulate the predators to leave the block and 

 search elsewhere for more abundant prey. If pest mites 

 were allowed to build beyond about 40% of leaves 

 infested, released predators might not be able to pro- 

 vide effective suppres- 

 sion. Foliage was 

 sampled for presence of 

 pest and predatory 

 mites in June (before 

 predators were re- 

 leased), in July (shortly 

 after predators were 

 released), and again 

 once each in August 

 and September. In an 

 attempt to control the 

 possibility that A falla- 

 cis appearing in the 

 aforementioned first- 

 and second-stage IPM 

 blocks might have been 

 progeny of resident A 

 fallacis (present before 

 the releases occurred) 

 or were natural immi- 

 grants from outside the 

 blocks, we compared 

 the numbers of A falla- 

 cis on leaves in these 6 

 orchards with those on 

 leaves in 6 similarly 

 treated and similarly 

 sampled first- and sec- 

 ond-stage IPM blocks 

 in 6 other orchards 

 where A fallacis were 

 not released. 



Results 



In the 2 orchards 

 where predators were 

 released in 1988 but 

 not in 1989, no native 

 A fallacis were seen in 



June before A fallacis were released. After release, the 

 average ratio of pest mite to A fallacis frequency on 

 leaves in 1988 was 5 to 1 both in second-stage and first- 

 stage blocks (Table 1). A ratio of 5 to 1 is generally 

 considered to indicate a high probability of effective 

 biological mite control, while a ratio of 10 to 1 is 

 indicative of only moderate probability of such control. 

 In no block in any orchard in either year were predators 

 other than A fallacis (such as yellow mites) sufficiently 

 abundant to have affected the ratio of pest mites to A 

 fallacis. In 1989, there were extremely few pest mites 

 in either type of block in these 2 orchards until Septem- 

 ber, well after danger of damage by mites had passed. 

 Interestingly, there were extremely few or no A 



Fruit Notes, Winter, 1990 



13 



