It appeared that there were few if any detectable 

 differences in the outcome of releases of A fallacis in 

 second-stage versus first-stage IPM blocks. It appears 

 that the released A fallacis, selected before release to 

 be resistant to organophosphate insecticides, may have 

 been able to withstand such pesticide treatments after 

 early June in the grower control blocks. We must 

 caution, however, that such resistance could eventu- 

 ally break down through introgression of genes from 

 wild-population A fallacis in cases where such popula- 

 tions are still susceptible to organophosphates. 



It was clear that releasing about 500 A fallacis 

 adults on every fourth tree in a block (as was done in 

 1988 in all blocks) does not guarantee effective biologi- 

 cal control of pest mites either that year or the following 

 year. In 2 orchards, effective biological control did 

 occur (Table 1). In 4 orchards, moderate to relatively 

 little biological control occurred (Table 2). The pros- 

 pect for effective biocontrol within the same year of 

 release improved considerably when about 1500 A 

 fallacis adults per every fourth tree were released, as 

 was done in 1989. Still, we must wait to see if this very 

 high level of release will result in year-long suppression 



of pest mites in 1990 and thereafter. 



Finally, we must be patient. The full story of just 

 how effective are releases of A fallacis in apple or- 

 chards, compared with the alternative option of allow- 

 ing native A fallacis to build in the complete absence of 

 insecticide or miticide use after early June, may not be 

 known for at least a couple of more years, after contin- 

 ued future sampling in the 6 experimental orchards 

 where releases have been made and in the 6 compa- 

 rable orchards where no releases have been (or will be) 

 made. Researchers in the Netherlands believe that it 

 takes at least 4 years to see the full benefits of releasing 

 Typhlodromus pyri mite predators in Dutch orchards. 

 For now, we reserve full judgement and can only wait 

 to see what unfolds in 1990 and 1991. 



Acknowledgments 



We thank the Massachusetts Society for the Pro- 

 motion of Agriculture and federal/state agencies 

 granting apple IPM funds for supporting our work on 

 this project. Special thanks to Katharine Rankin and 

 Cheryl Donovan for their assistance, and Roy Van 

 Driesche for his helpful advice. 



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16 



Fruit Notes, Winter, 1990 



