mite predators, corresponding percentages were 

 19.8, 9.5, and 7.2. Remaining batches were 

 classified by both IPM scouts and lab exam as 

 having no predators. 



Conclusions 



Our findings indicate that the presence of 

 predatory mites was detected more often under 

 a microscope than by IPM scouts, particularly in 

 the case of phytoseiids. In fact, among ail leaves 

 examined, phytoseiids were detected more than 

 four times as often and stigmaeids more than 

 twice as often under a microscope than by IPM 

 scouts. 



At least three factors may have contributed 

 to this pattern of results. First, the greater 

 magnifying power of a microscope may have 

 facilitated detection of small, newly-hatched 

 predators that are difficult to detect using an 

 Optivisor or hand lens. Second, at least six IPM 

 scouts were involved over the growing season in 

 examining leaves for mites in orchards, and 

 there may have been substantial variation 

 among these scouts' ability to detect and iden- 

 tify predators. In contrast, the same person 

 performed all of the examinations under the 

 microscope. Third, there may have been some 

 redistribution of predators among leaves during 

 transport to the laboratory, possibly resulting in 



the spread of predators to a greater prop>ortion of 

 leaves. We believe, however, that this factor 

 was minor compared with the first two factors. 



Regrettably, our findings suggest that a 

 grower (who might be less skilled than an IPM 

 scout in identif5ring mite predators) cannot rely 

 on his or her counting of mite predators using a 

 hand lens or Optivisor as providing an accurate 

 assessment of the level of predators actually 

 present. New York state IPM personnel have 

 recognized this shortcoming and have created a 

 tripartite sampling procedure for pest mites 

 that excludes the need to sample for and identify 

 mite predators. A slightly modified version of 

 this procedure for use by Massachusetts grow- 

 ers is described in detail in the 1994 March 

 Message to Massachusetts Fruit Growers. 



In sum, we will continue to sample for mite 

 predators in our monitored test and check IPM 

 blocks but recommend that growers use caution 

 in interpreting their mite predator monitoring 

 results. Predators could be more abundant than 

 meets the eye. 



Acknowledgments 



This work was supported by grants from the 

 Massachusetts Society for Promoting Agricul- 

 ture and the USDA Northeast Regional IPM 

 Competitive Grants Program. 



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Fruit Notes, Summer, 1994 



21 



