1 INCH 



4 INCHES 



X 



0.001 0.01 0.1 



jU 



0.001 0.01 0.1 



7 INCHES 



10 INCHES 



100 



S 50 



■ : 



50 



1^ 



0.001 0.01 0.1 1 



0.001 0.01 0.1 1 



CONCENTRATION OF SPINOSAD 



Figure 4. Percent mortality of flies 72 hours after exposure for 10 minutes in laboratory cages to spheres topped by discs 

 that contained different concentrations of spinosad (0 to 1.0%) and received 1, 4, 7, or 10 inches of artificial rainfall 

 before testing. Each value is based on sphere exposure to 20 flies (10 flies per sphere x 2 spheres per treatment). 



2003-version PTS (regardless of dose of spinosad) at 

 6, 9, and 12 weeks of field exposure (Figure 3), during 

 which cumulative totals of about 11,13, and 21 inches 

 of rain fell on the PTS. 



Results of Experiment 3 (Figure 4) show that among 

 adults placed on 2003-version PTS exposed to artificial 

 rainfall of 1 , 4, 7, or 10 inches, mortality of adults after 

 10 inches of rainfall was 0, 10, 55, 85, and 95% for 

 spheres having discs containing 0, 0.001 , 0.01 , 0. 1 , and 

 1 .0% spinosad, respectively. Additional results for 

 spheres exposed to 10 inches of rainfall revealed that 

 about 25% of adults placed on spheres moved onto the 

 disc, irrespective of amount of toxicant in the disc (data 

 not shown). Data in Figure 5 show that regardless of 

 the dose of spinosad in the disc, 71-93% of flies that 

 remained on the sphere surface (after placement there) 

 fed for at least 10 seconds and 67-100% of flies that 

 moved onto the disc (after placement on the sphere 



surface) fed on the disc. Mortality of flies that remained 

 on the sphere surface ( 79-9 1 %) or moved onto the disc 

 ( 1 00%) was high for discs having 0. 1 or 1 .0% spinosad 

 but was lower (50-56%) for discs having a 0.01% 

 spinosad and very low (0-7%) for discs having 0.00 1 % 

 spinosad. Combined results from Experiment 3 suggest 

 that after receiving 1 inches of artificial rainfall, disc- 

 topped PTS receive enough sugar to stimulate a high 

 proportion of adults to feed on the sphere surface but 

 an insufficient amount of toxicant to kill a high 

 proportion of adults at doses of spinosad of 0.01% or 

 less. 



Conclusions 



Results of all three experiments conducted in 2003 

 pave the way for a new type of pesticide-treated sphere 

 for control of apple maggot. The new type (our 2003- 



24 



Fruit Notes, Volume 69, Spring, 2004 



