Pursuit of Effective Pesticide-treated 

 Spheres for Controlling Apple Maggot 



Starker Wright, Bradley Chandler, Russell Fleury, and Ronald Prokopy 

 Department of Entomology, University of Massachusetts 



For many years, we have reported in Fniil Notes progress 

 toward development of effective trapping systems for behav- 

 ioral control of apple maggot fly (AMF). Until recently, the 

 bulk of this research has been built upon deployment of sticky- 

 coated red spheres for direct control of AMF. Exhaustive 

 field research has convincingly shown that sunounduig mid- 

 sized blocks (trials performed in plots up to -ten acres) with 

 odor-baited sticky red spheres (five yards apart) to intercept 

 immigrating AMF can provide very good control witliout need 

 for summer insecticides. However, the sticky material used 

 to trap and kill alighting AMF is very difficult to handle and 

 requires frequent maintenance to ensure trap effectiveness. 



To address this shortcoming, we have developed and 

 tested a series of prototype pesticide-treated spheres (PTS) 

 to substitute for cumbersome sticky-coated spheres. In con- 

 cept, AMF land on a PTS, receive a toxic dose of insecticide, 

 and die. However, consistent lethality to AMF can only be 

 assured if flies are strongly induced to feed upon the sphere 

 surface and ingest a very small (but lethal) dose of insecti- 

 cide. Because of this, PTS must maintain a detectable resi- 

 due of feeding stimulant (such as sucrose) associated with 

 toxicant at the sphere surface. Unfortunately, under condi- 

 tions of rainfall, both insecticide and sucrose lose residual 

 activity very quickly. Latex paint is very effective in pre- 

 serving residual activity of insecticide — we have evaluated 

 all orchard-labeled insecticides and have found imidacloprid 

 (Provado) to be the most toxic to AMF at a very low dose in 

 latex paint. In fact, a dose of 2%-4% (a.i.) imidacloprid in 

 latex paint is sufficient to kill 80% of flies alighting on wooden 

 PTS after 12 weeks of field exposure (and 12 inches of rain- 

 fall), provided that PTS have been retreated with feeding 

 stimulant. Thus, the key to successful development of com- 

 mercially viable PTS for direct control of AMF lies in main- 

 taining the residual effectiveness of sucrose on spheres un- 

 der field conditions. Although the problem can be stated 

 simply (maintain sugar on spheres throughout a northeastern 

 summer), we have struggled for many years to achieve a firm 

 solution. 



Materials & Methods 



We have developed two approaches to providing a con- 

 tinuous supply of sucrose on the surface of a PTS to ensiu'e 



fly feeding and consistent toxicity to AMF. In 1999, we de- 

 veloped a prototype disc comprised of sucrose bound in par- 

 affin wax that is placed atop a wooden PTS (as described in 

 Fruit Notes, Fall 1999). Under rainfall, sugar is distributed 

 along with water onto the sphere surface, renewing sucrose 

 lost from the sphere surface during runoff For deployment 

 in 2000, we modified these sucrose/wax caps in three major 

 ways: (a) we doubled the mass of the cap to 50 grams to 

 extend the endurance of each cap; (b) we increased the di- 

 ameter to 2 in. (from 1.25 in.) to maximize surface area and 

 sucrose output; and (c) we designed a hydraulic mold system 

 that presses eight flutes into each cap to ensure uniform dis- 

 tribution of sucrose-bearing runoff". 



Our second approach involved a collaborative effort 

 (with the USDA lab at Peoria, IL) toward development of a 

 sphere whose entire body consists of a mixture of sugar and 

 starches (as reported in Fruit Notes, Fall 1997), such that 

 under rainfall, sugar is emitted through the latex paint onto 

 the sphere surface. Both of these sphere types have under- 

 gone extensive laboratory testing, revision, and fine-tuning 

 in the past several years. Here, we report on commercial- 

 orchard trials of our best versions of each sphere type for the 

 2000 growing season. 



In 28 small plots (~49 trees each) of apple trees across 

 seven commercial orchards, we compared the effectiveness 

 of our newest versions of PTS (Figure 1) against sticky 

 spheres and insecticide sprays for control of AMF. Both 

 wooden and sugar/flour PTS were treated with latex paint 

 containing 2% (a.i.) imidacloprid. For this trial, three plots 

 per orchard were equipped with spheres positioned about five 

 yards apart on all perimeter trees, and one grower-sprayed 

 plot served as the orchard control. One plot of each experi- 

 mental treatment was emplaced in each orchard: (a) wooden 

 PTS bearing a 50 gram cap of 85% sucrose: 15% paraffin 

 wax (each cap 2 in. diameter, fiuted for even runoff distribu- 

 tion); (b) sugar/flour PTS produced by a private manufac- 

 turer (FruitSpheres Inc.), distributed alternately with either 

 black or red paint (to gauge rodent-deterrent effects of sphere 

 color); (c) sticky-coated wooden spheres; and (d) two to three 

 insecticide sprays. Caps atop wooden spheres and all sugar/ 

 flour spheres were replaced at mid-season (after six weeks 

 of field exposure) with fresh versions of each. Treatment 

 effectiveness was judged by comparing numbers of feral AMF 



Fruit Notes, Volume 65. 2000 



45 



