Evaluation of Varying Doses of Different 

 Toxicants for Use on Spheres to Control 

 Apple Maggot Flies 



Ronald Prokopy, Starker Wright, Brad Chandler and Xingping Hu 

 Department of Entomology, University of Massachusetts 



In the 1997 Fall issue of Fruit Notes, we re- 

 ported that imidacloprid was a promising alterna- 

 tive to dimethoate as a toxicant for application to 

 pesticide-treated spheres for controlling apple mag- 

 got flies (AMF). We also reported that imidacloprid 

 at 1.5% active ingredient (a.i.) in paint afforded 

 longer residual activity than imidacloprid at 0.5% 

 a.i. in paint, and that a Merit 75 WP formulation 

 of imidacloprid in paint was more effective than a 

 Provado 1.6 F formulation in paint at 0.5% a.i., 

 though not at 1.5% a.i. 



The unusually large numbers of AMF in some 

 Massachusetts commercial apple orchards in 1998 

 allowed early-season direct observations of the 

 behavior of AMF after alighting on imidacloprid- 

 treated spheres. These observations suggested to 

 us that by increasing the dose of imidacloprid on 

 spheres beyond the 1.5% active ingredient used 

 heretofore, we might be able to capitalize on con- 

 tact-type toxicity of imidacloprid, thus diminish- 

 ing the need to maintain feeding stimulant (sucrose) 

 on the sphere surface. Such a high-dose approach 

 was thought previously to be impractical, owing 

 to the handling risk associated with higher doses 

 of our originally-adopted toxicant, dimethoate. 



Here, we report on 1998 studies of AMF re- 

 sponses to four different doses of imdacloprid in 

 latex paint, with and without the addition of su- 

 crose as feeding stimulant. We also report on AMF 

 responses to three new candidate toxicants: 

 spinosad, sugar ester, and fipronil. All three, like 

 imidacloprid, are considered to be comparatively 

 safe for handling by humans. 



Materials & Methods 



In our first test, we painted the inside surface 

 of small plastic cups with a mixture of Glidden 



Red Latex Gloss Enamel paint and either 0.1, 0.5, 

 1.0, or 5.0% a.i. of one of the following potential 

 toxicants: imidacloprid (Merit 75 WP), spinosad 

 (SpinTor 22.8 F), sugar ester (SCO 3483, 100%), 

 or fipronil (Regent 80 WG). No sugar was added 

 to any mixture. After the mixture dried, 10 AMF 

 were confined in each of two cups of the same treat- 

 ment type for 10 minutes, following which AMF 

 were transferred to clean cups supplied with food 

 and water. Mortality was assessed after 72 hours. 



For our second test, we focused on the two 

 toxicants that showed the most promise in the first 

 test: imidacloprid and fipronil. Each of these toxi- 

 cants was evaluated at 2, 4, 8, and 16% a.i. in 

 Glidden Red Latex Gloss Enamel paint (no sugar 

 added) applied to wooden spheres. After drying, 

 spheres were hung in orchard trees and returned 

 to the laboratory after 3, 6, 9, or 12 weeks for 

 evaluation of toxicity to AMF. For evaluation, 30 

 AMF were placed individually on a sphere of each 

 treatment type and allowed to remain 10 minutes, 

 following which AMF were transferred to small, 

 clean cups supplied with food and water. Mortal- 

 ity was assessed after 24 hours. Half of the spheres 

 of each treatment type received a 20% sucrose so- 

 lution just prior to testing. The other half received 

 no sucrose. 



For our third test, we again focused on 

 imidacloprid and fipronil, but in this experiment, 

 we evaluated the behavior of sphere-exposed AMF 

 shortly after removal from spheres. Spheres were 

 treated with 2.0% a.i. imidacloprid or fipronil in 

 Glidden Red Latex Gloss Enamel paint and exposed 

 for 3 weeks in orchard trees. Just before testing, 

 all spheres received a 20% sucrose solution. For 

 each treatment, 32 AMF were placed individually 

 on a sphere and allowed to feed for up to 10 min- 

 utes. One hour after feeding, each fly was trans- 



Fruit Notes, Volume 63 (Number 4), Fail, 1998 



