100 



Q. 

 (0 



c 

 o 



_c 

 'E 

 "(5 

 E 



0) 



O) 



3 

 <0 



"« 



c 

 5) 



1 2 3 4 5 6 7 



Inches of artificial rainfall 



Figure 2. Percent of original sugar remaining on four different types of spheres following expo- 

 sure to artificial rainfal. 



times caused the spheres to turn whitish under high 

 humidity conditions. 



The average amount of dimethoate residue on 

 the surface of toxicant-treated spheres (T3rpe B) 48 

 hours after sphere deployment was only about one- 

 fifth the amount on the surface of apple foliage 

 sprayed with dimethoate 48 hours earlier (Table 1). 

 At 48 hours, essentially no residue was present on 

 the surface of apple fruit. Apparently the 

 dimethoate had been absorbed by the fruit flesh, 

 which is a property of dimethoate that confers its 

 well-known long-residual systemic activity to insect 

 larvae feeding on fruit flesh. Even after one month 

 of field exposure, during which 2.8 inches of rain 

 fell, the amount of dimethoate on the surface of 

 apple foliage and Type B spheres remained at nearly 

 the same levels as at 48 hours. 



Conclusions 



The most effective toxicant-treated wooden 

 sphere developed through our 1995 research efforts 



represents a substantial improvement over our 1994 

 version. This was accomplished mainly by apply- 

 ing three layers of mixture to the sphere surface to 

 create better retention of sugar (fly feeding stimu- 

 lant) present in the first layer. For deployment for 

 apple maggot fly control in orchards, we would like 



12 



Fruit Notes, Spring, 1996 



