to see at least 70% kill of all flies that alight on a 

 sphere. This is the approximate level of kill cur- 

 rently provided by sticky-coated red w^ooden spheres 

 one week afterdeployment. Sticky-coated spheres 

 require frequent cleaning to maintain this level of 

 kill. Type D spheres received a third-layer coating, 

 consisting of shellac, that provided 70% kill of alight- 

 ing flies five weeks after deployment, during which 

 slightly more than three inches of rain fell. 



We consider this to be an important step for- 

 ward in the development of toxicant-treated 

 spheres. Still, there remains much research to be 

 done to achieve our goal of 12 weeks of high re- 

 sidual activity. For example, there are two princi- 

 pal shortcomings to current Type D spheres. First, 

 for every rain event of one-fourth inch or greater 

 after about 3 inches of rainfall, type D spheres re- 

 quire retreating with a sugar-water mixture to re- 

 plenish at least some of the lost fly-feeding stimu- 

 lant. Second, the sphere surface may turn whitish 

 after exposure to high humidity, dew, or rainfall on 

 account of the moisture-absorbing properties of shel- 



lac. This reduces visual attractiveness of the 

 spheres to the flies. 



Even with these shortcomings, however, we are 

 encouraged to seek improvements not only because 

 of progress made in 1995 but also on account of the 

 safety of current spheres to those deploying or han- 

 dling spheres in an orchard. Indeed, the toxicologi- 

 cal date revealed that it is much safer to repeatedly 

 touch the surface of a dimethoate-treated sphere 

 (as currently formulated) than to repeatedly touch 

 the surface of apple foliage sprayed with a stan- 

 dard rate of dimethoate for maggot fly control at a 

 legally approved orchard-reentry time of 48 hours 

 after spra3dng. 



Acknowledgments 



We thank Joseph Reale and Isabelle Jacome for 

 assistance with assays of flies and sucrose and Andy 

 Curtis for assistance with the toxicology. This work 

 was supported by a grant from the USDA North- 

 east Region Apple IPM program and Hatch 608. 



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Fruit Notes, Spring, 1996 



13 



