fourth plot received two or three sprays of phosmet to 

 control AMF. Discs atop wooden spheres and all sugar/ 

 flour spheres were replaced at mid-season (after 6 

 weeks of field exposure) with fresh versions of each. 

 Treatment effectiveness was judged by comparing 

 numbers of feral AMF captured on interior unbailed 

 monitoring traps (four traps on central trees of each 

 plot) and percent injury to fruit in samples taken every 

 other week from July to September. 



In addition to measurements of whole-plot 

 treatment effectiveness, we assessed the structural 

 durability of each PTS bi-weekly from .July to 

 September. For these assessments, we recorded the 

 percentage of spheres impacted by feeding of rodents 

 or other mammals on discs atop wooden spheres or on 

 the body of sugar/flour spheres. For each of four 

 sample sites, we also recorded the amount of rainfall 

 accumulated during each bi-weekly period as a factor 

 potentially leadmg to premature breakdown of sphere 

 effectiveness (through wash-off of sugar and/or 

 toxicant). 



At the mid-point (6 weeks of sphere exposure) and 

 end (12 weeks of sphere exposure) of our trial, we 

 retrieved two randomly-chosen but intact PTS of each 

 type from each orchard and returned them to the 

 laboratory for testing. We directly assessed the fly- 

 killing power of each 

 retrieved PTS by exposing 1 

 AMF to the sphere. Each PTS 

 was tested twice: soon after 

 return from the field (with no 

 supplemental feeding 



stimulant applied to the 

 sphere), and again after 

 application of a 20% sucrose 

 solution to stimulate fly 

 feeding. Residence time on 

 spheres and condition (alive 

 or dead) at 72 hours post- 

 exposure were recorded for 

 each fly. 



AMF that penetrated into plots surrounded by wooden 

 PTS were substantially fewer (~ 30% fewer) than the 

 numbers that penetrated into plots surrounded by sugar/ 

 flour PTS or sticky spheres and were only about 3% 

 greater than the number that penetrated into insecticide- 

 treated plots (Table 1). Very few sampled fruit were 

 injured by AMF in plots surrounded by wooden PTS 

 (0.13%) or sticky spheres (0.13%) or in plots sprayed 

 with insecticide (0. 1 7%), whereas a greater percentage 

 was injured in plots surrounded by sugar/flour spheres 

 (0.58%) (Table 1). 



Structural Integrity. Data in Table 2 show that after 

 6 weeks of field exposure from early July until mid- 

 August, 37% of sugar/fiour PTS but only 10% of sugar/ 

 wax discs atop wooden PTS had lost 20% or more of 

 their surface area to feeding by rodents or other 

 mammals. All of the feeding on sugar/wax discs 

 occurred in a single orchard and was perpetrated by 

 raccoons, which were observed to be numerous in that 

 orchard. All sugar/flour PTS and all discs atop wooden 

 PTS were replaced at mid-August. By mid-September 

 (4 weeks later), 47% of sugar/flour PTS but 0% of discs 

 atop wooden PTS had lost 20% or more of their surface 

 area due to feeding by vertebrates. 



Residual Sugar. As depicted in Figure 1 , the amount 

 of sugar remaining in sugar/wax discs atop wooden 



Results 



Treatment Effectiveness. 

 As indicated by captures of 

 AMF on unbaited monitoring 

 spheres on interior trees of 

 each plot, the numbers of 



Table 1. Captures of feral AMF on unbaited monitoring traps and 

 percent injury to fruit by AMF in 24 plots of apple trees in six 

 commercial orchards in 2001. 



Treatment* 



No. AMF 

 captured 

 per plot** 



Fruit injury 

 per plot (%)*** 



Wooden PTS 

 Sugar/flour PTS 

 Sticky Spheres 

 Insecticide Sprays 



38.1 

 54.5 

 53.0 

 36.9 



0.13 

 0.58 

 0.13 

 0.17 



Within columns, differences among treatments were 

 nonsignificant at odds of 19 to 1 . 

 Based on four unbaited spheres per plot. 

 Based on 100 fruit sampled per plot on each of five bi- 

 weekly sampling dates from July to September. 



Fruit Notes. Volume 66. 2001 



31 



