Comparison of Provado™ and Actara™ 

 as Toxicants on Pesticide-treated 

 Spheres 



Starker Wright, Bradley Chandler, and Ronald Prokopy 

 Department of Entomology, University of Massachusetts 



As reported in previous issues of Fruit Notes, we 

 believe that behavioral control using red spheres holds 

 potential as an eventual replacement for use of insecti- 

 cidal sprays against apple maggot flies (AMF). To- 

 ward this, we have developed pesticide-treated spheres, 

 which are designed to kill alighting flies either by con- 

 tact with or ingestion of a lethal dose of insecticide, 

 which is bound in latex paint coating the sphere. Such 

 an advance may alleviate the need for use of Tangletrap 

 on spheres, which currently renders spheres too costly 

 and laborious for wide-scale commercial use. 



For spheres to become a viable alternative to 

 chemical treatments for AMF control, we believe that 

 four criteria must be met. Spheres must be: 



1) easy and safe to deploy and maintain 



2) as effective as insecticide sprays 



3) able to endure through the 12-14 week 

 AMF season 



4) capable of maintaining fly-killing power 

 with a very low dose of toxicant 



Over the past 3 years, we have moved toward sat- 

 isfying, but have not fully satisfied, all of the above 

 criteria. Additional articles within this issue (see 

 Attracticidal Spheres) highlight studies of the effi- 

 ciency of various sphere types. Here, we present find- 

 ings of a 1999 comparison of toxicants intended for 

 use on spheres: imidacloprid (Provado) and 

 thiamethoxam (soon to be labeled as Actara). 



Materials & Methods 



We formulated three rates each (2, 4, and 8%) of 

 imidacloprid and thiamethoxam in latex paint and ap- 

 plied each mixture to 8-cm red wooden spheres (~3 

 grams per sphere). At each dose of each chemical, we 

 prepared ten spheres, then subjected two spheres of 

 each treatment to 0, 3, 6, 9, or 12 weeks of field expo- 



sure (encompassing the normal Massachusetts AMF 

 season). For each treatment set, we also prepared and 

 exposed two control spheres (treated with latex paint 

 alone). In all, we used 70 wooden spheres in this ex- 

 periment. 



One set of spheres was retained in the laboratory 

 for immediate testing (0 weeks field exposure) We 

 placed all other spheres in a block of unsprayed, me- 

 dium-sized Delicious apple trees on June 30. At 3- 

 week intervals thereafter, we retrieved one set of 14 

 spheres for testing; spheres were removed from the field 

 for assays on July 19 (3 weeks), August 10 (6 weeks), 

 September 1 (9 weeks), and September 22 (12 weeks). 

 Throughout the time of study, we recorded daily rain- 

 fall using a Campbell weather monitoring station. 



Upon return to the lab, we performed two assays: 

 exposure and subsequent mortality of flies on spheres 

 without addition of feeding stimulant (yielding rela- 

 tive contact activity of toxicants) and exposure and 

 mortality of flies on spheres after treatment with a 20% 

 sucrose solution (yielding activity of toxicants after 

 ingestion). We exposed thirty flies (individually) to 

 each treatment, recorded time spent feeding or forag- 

 ing on spheres, and assessed levels of fly mortality at 

 24, 48, and 72 hours post-exposure. 



Results 



Contact Toxicity (no feeding stimulant) 



For spheres tested prior to weathering, exposure 

 of flies to spheres treated with either chemical at any 

 rate yielded mortality no higher than 45% (Figure 1). 

 Subsequent tests of field-exposed spheres offered even 

 lower contact toxicity (at all rates), with the exception 

 of spheres exposed six weeks, which resulted in fly 

 mortality nearly identical to unweathered spheres. 



Fruit Notes, Volume 64 (Number 4), Fall, 1999 



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