Progress in 1995 Toward Development of 

 Toxicant-treated Spheres for Controlling 

 Apple Maggot Flies 



Xingping Hu, John Clark, and Ronald Prokopy 

 Department of Entomologyy University of Massachusetts 



Previous Fruit Notes have addressed the poten- 

 tial of using toxicant-treated spheres for control- 

 Ung apple maggot flies. Our ideal toxicant-treated 

 sphere would be one that 1) employs only a small 

 amount of safe toxicant, 2) encourages an alighting 

 fly to feed voraciously upon arrival and thereby to 

 ingest the toxicant, 3) possesses at least 12 weeks 

 of effective residual activity, and 4) is safe to handle 

 and deploy. 



Here, we report on results of comparisons be- 

 tween the 1994 version of toxicant-treated sphere 

 and three of the most promising sphere prototypes 

 developed during 1995. Specifically, we present in- 

 formation on sphere composition, degree of toxicity 

 to maggot flies before and after varying amounts of 

 rainfall, and safety of spheres for handling and de- 

 ployment. 



Materials & Methods 



All spheres reported on here were wooden, 3 

 inches in diameter, and coated by brush with one 

 or more layers of liquid material. Compositions of 

 coating were as follows: 



Type A. 1994 version, consisting of a single layer 

 of a mixture containing 2% Digon 4E (1.0% 

 dimethoate as the active toxic ingredient), 40% 

 Glidden gloss red latex paint, and 58% granulated 

 table sugar (sucrose). 



Type B. Two layers of mixture. First layer con- 

 sisted of 20% Glidden flat red latex paint, 76% 

 granulated table sugar, and 4% wheat flour. Sec- 

 ond layer consisted of 1% Digon 4E and 99% of the 

 same paint. 



Type C. Three layers of mixture. First two layers 

 were same as for Tjrpe B. Third layer was linseed 

 oil. 



Type D. Three layers of mixture. First two layers 

 were same as Type B. Third layer was shellac. 



In all cases, spheres were allowed to dry (usu- 



ally 1-2 days) between applications of layers and 

 before deployment. In some cases, a small amount 

 of water was added to the final mixture of the first 

 and second layers to facilitate brushing. 



To assess toxicity of each type of sphere to apple 

 maggot flies, 12 spheres of each type were hung from 

 branches of apple trees at the University of Massa- 

 chusetts Horticultural Research Center 

 (Belchertown) in early July. After 0, 1, 3, 5, 7, and 

 10 weeks, two spheres of each type were brought to 

 the laboratory for toxicity assays. Thirty flies were 

 released individually onto each sphere (total of 60 

 per sphere type) and allowed to remain there up to 

 ten minutes. After exposure, each fly was kept in a 

 small cup for 24 hours to assess mortality. Flies 

 originated frompupae collected from nature, 

 emerged in laboratory cages, were 12 to 15 days old 

 when tested, and were starved of all food 10 to 15 

 hours prior to testing. 



To determine the effect of rainfall on loss of fly 

 feeding stimulant (sucrose), separate sets of spheres 

 of each type were hung in a laboratory chamber 

 that delivered artificial rainfall at a rate of one inch 

 per hour. This was done for one hour per day over 

 seven successive days, with 23 hours of drying time 

 between rainfall exposure events. Runoff from each 

 sphere was collected and submitted to chemical 

 analysis for percent sucrose content. 



Finally, we compared the safety of handling 

 dimethoate-treated spheres with the safety of han- 

 dling apple foliage and fruit treated with a spray of 

 dimethoate. In early August, several apple trees at 

 the Horticultural Research Center received a spray 

 of Digon 4E applied by air blast sprayer at the 

 equivalent of 300 gallons water per acre. The 

 amount of Digon 4E used was 16 ovmces per 100 

 gallons water, which is the label-recommended rate 

 for control of apple maggot flies. Immediately fol- 

 lowing spraying, we hung several freshly-prepared 

 Type B pesticide-treated spheres on adjacent apple 

 trees. At designated intervals after spraying. 



10 



Fruit Notes, Spring, 1996 



