fallacis predators found in these orchards in 1989. The 

 near total absence of pest mites in June, July, and 

 August may have stimulated the A fallacis to leave the 

 blocks and search elsewhere for prey. A fallacis do not 

 remain long on foliage harboring few potential prey. 

 The results in these 2 orchards suggest that A fallacis 

 eventually provided good suppression of pest mites in 

 both the second-stage and the first-stage control blocks 

 in 1988 and that a high level of suppression occurred 

 through August of 1989. The near absence of A fallacis 

 in our samples of September, 1989 in these 2 orchards 

 makes us wonder, however, if enough A fallacis will be 

 on hand in 1990 to provide effective suppression of pest 

 mites. 



In the 4 orchards where predators were released in 



both 1988 and 

 1989, again no 

 native A fallacis 

 were found in 

 June 1988, before 

 A fallacis were 

 released. After 

 release, the aver- 

 age ratio of pest 

 mite to A fallacis 

 frequency on 

 leaves in 1988 was 

 8 to 1 in the sec- 

 ond-stage blocks 

 versus9tolinthe 

 first-stage blocks 

 (Table 2). This 

 result suggests 

 that a moderate 

 level of biological 

 control was 



reached. By late 

 June of 1989, 

 however, pest 

 mites had reached 

 average frequen- 

 cies of 32 and 29% 

 of leaves infested 

 in the second- 

 stage and first- 

 stage blocks, re- 

 spectively (Table 

 2). These fre- 

 quencies are only 

 slightly less than 

 the tolerable level 

 of pest mite popu- 

 lations on apple 

 trees in late June. 

 No A fallacis were found in any of the blocks in these 

 4 orchards in June. Conceivably, in these orchards, 

 early-season use in 1989 of pesticides to which the 

 released predators were not tolerant may have contrib- 

 uted to their lack of appearance in detectable numbers. 

 After release of veiy large numbers of A fallacis in July 

 of 1989 in these orchards, the average ratio of pest mite 

 to A fallacis frequency on leaves was 4 to 1 in both the 

 second-stage and first-stage blocks. These ratios sug- 

 gest that a high level of biological pest mite control 

 occurred in these 4 orchards. It will be most interesting 

 to see whether the high numbers of A fallacis present 

 in these 4 orchards in September of 1989 carry over to 

 provide effective biocontrol of pest mites in 1990. 

 It would be wrong to conclude from the foregoing 



14 



Fruit Notes, Winter, 1990 



