O' Say Can You See Mite Predators in 

 Apple Orchards? 



Ronald J. Prokopy, Xingping Hu, and Jennifer Mason 

 Department of Entomologyy University of Massachusetts 



Most apple growers recognize the impor- 

 tance of spider mites as potential pests and 

 predatory mites as potential beneficials in or- 

 chards. We in fruit research and extension often 

 advise growers to scout trees both for predatory 

 mites and pest mites before deciding whether or 

 not to apply a miticide. The ratio of predatory to 

 pest mites frequently is used as one of the bases 

 for a spray decision. If there are one or more 

 predators to every five pest mites, then there is 

 reason to believe that predators can provide 

 effective control without pesticide treatment. 

 Making such a determination through scouting 

 sounds simple enough, but in fact, it is quite 

 demanding. Sampling a representative set of 

 leaves in the orchard is difficult, but even more 

 difficult is seeing predatory mites emd distin- 

 guishing them from pest mites or mites that are 

 neither friend nor foe. 



Here, we report on a study conducted in 

 1993 in which mite predator abundance on tree 

 leaves assessed in the field by IPM scouts com- 

 pared with mite predator abundance on tree 

 leaves taken to the laboratory and examined 

 under a microscope by a skilled mite taxono- 

 mist. 



Materials & Methods 



We sampled leaves an average of 12 times 

 (May to September) from a second-level IPM 

 test block and an adjacent first-level IPM check 

 block in each of 12 orchards, for a total of 298 

 sample events. For each event, we picked 10 

 leaves at random from each of 20 trees. All 10 

 leaves from each tree were examined immedi- 

 ately by one or another member of the six- 

 member IPM scouting team using an Optivisor 

 (3x power). Five of these leaves (chosen at ran- 

 dom) were placed immediately in a cooler and 



returned the same day to a refrigerator at 40F 

 in our laboratory, where soon afterward they 

 were examined under a microscope ( 15x power). 

 In all, 59,600 leaves were examined in the field 

 and 29,800 in the laboratory. We did not count 

 every predator seen. Rather, we recorded the 

 percentage of leaves in each 100-leaf batch that 

 had predatory mites. 



Results 



Of all sampled leaves, only 0.8% were ob- 

 served to have phytoseiid mite predators (ivory- 

 colored Amblyseuis fallacis or ivory colored 

 Typhlodromus pyri) by IPM scouts in orchards 

 compared with 3.5% under a laboratory micro- 

 scope (Table 1). For stigmaeid mite predators 

 (yellow-coloredZetee//ia mali), percentages were 

 2.2 and 5.5, respectively. 



Among the 298 batches of sampled leaves, 

 17.9% were classified by both IPM scouts and 

 lab exam as having phytoseiids present, 9.8% 

 were classified by lab exam but not by IPM 

 scouts as having phytoseiids, and 4.8% were 

 classified by IPM scouts but not by lab exam as 

 having phytoseiids (Table 2). For stigmaeid 



Table 1. Percent of all sampled leaves 

 observed as having mite predators by 

 IPM scouts in orchards versus by exami- 

 nation under a microscope in the labora- 

 tory. 



Type of 

 predator 



IPM 

 scouts 



Laboratory 

 microscope 



Phytoseiid 

 Stigmaeid 



0.8 

 2.2 



3.5 

 5.5 



20 



Fru'n Notes, Summer, 1994 



