artificial rainfall exposure. Sucrose bound in each cap 

 was stained with a water-soluble, food-grade dye to 

 permit visual observation of the movement and relative 

 concentration of sucrose dissolved in runoff water. In 

 addition, spheres were painted gloss white to allow 

 maximum visual interpretation of sucrose coverage and 

 distribution. All runoff water from each sphere was 

 collected and tested for sucrose content using a Brix 

 scale assessed with an Atago hand refractometer (0- 

 32%, +/-0.I%). 



In our first experiment, we varied the concentration 

 of paraffin m each cap to assess the impact of paraffin 

 content on sugar output and cap durability. We formed 

 two-inch fluted caps (50 grams each) contammg 10%, 

 15%, 20%, or 25% paraffin, and subjected five 

 replicates of each disc type to eight inches of artificially 

 applied rainfall. In all trials of these caps, rain was 

 applied at a rate of one inch per hour, and spheres 

 received no more than one inch per day to simulate the 

 periodic rains of summer field conditions. After each 

 inch of rainfall, we calculated the total mass of sugar 

 put out by each cap, the mass of sugar lost to rainfall 

 (by collecting and analyzing runoff water from each 

 sphere), and the amount of sugar left on the surface of 

 each sphere. Initial data drawn from caps containing 

 15% and 20% paraffin were encouraging, leading us 

 to test the acceptability of spheres to flies after two, 

 four, six, and eight inches of rainfall. In this trial, 50 

 flies were exposed (individually) to each treatment. 

 Flies were allowed to forage freely on spheres for a 

 maximum of 600 seconds. Total residence time and 

 time spent feeding were recorded for each fly. 



In our second experiment, we varied the total mass 

 and diameter of caps in an attempt to heighten both 

 the concentration and duration of the sugar output of 

 each cap. For this trial, we produced three types of 

 caps: 1) 2-inch diameter, 50 grams, fluted; 2) 2-inch 

 diameter, 75 grams, fluted; and 3) 2'/2-inch diameter, 

 75 grams, fluted. As in the previous experiment, we 

 subjected five replicates of each cap type to eight inches 

 of artificially applied rainfall in one-inch increments. 

 After each rainfall interval, we assessed the total mass 

 of sugar put out by each cap, the mass of sugar lost to 

 runoff, and the amount of sugar left on the surface of 

 each sphere. Given the limited success of either of the 

 larger caps, we did not perform fly feeding tests on 

 any spheres in this experiment. 



In our third experiment, we attempted to enhance 

 the performance of sugar-release caps by capitalizing 



on the observation that a small amount of water is 

 absorbed by and moves through the paraffin/sucrose 

 matrix of each cap. To enhance the availability of 

 sucrose bound within the wax matrix, we reshaped our 

 2000 field-standard caps (15% paraffin, 2-inch 

 diameter, 50 grams) such that eight shallow reservoirs 

 were pressed into the top of each cap. As an alternative 

 to fluted caps that channel rainfall off of wax/sugar 

 caps, these caps were designed to retain a small amount 

 of water (roughly five milliliters) in reservoirs atop 

 each cap, allowing held water to percolate through the 

 slightly porous cap body. This percolation effect has 

 four advantages over previous cap styles; 1 ) the slowly 

 developing sucrose-bearing runoff is highly 

 concentrated to consistently stimulate fly feeding; 2) 

 very little sucrose runs ofl'onto fruit and foliage beneath 

 traps, limiting fungal growth; 3) the entire mass of 

 sucrose in each cap is eventually used, dramatically 

 increasing the endurance of each wooden PTS; and 4) 

 a very small amount of rainfall or dew (less than 0.1 

 inch) is needed to recharge the spheres with sucrose. 

 In this experiment, we directly compared these 

 modified caps with our 2000 field standard. As in 

 previous trials, five spheres of each type were exposed 

 to artificially generated rainfall in 1-inch increments. 

 After each rainfall interval, we assessed the total mass 

 of sugar put out by each cap, the mass of sugar lost to 

 runoff, and the amount of sugar left on the surface of 

 each sphere. 



Our final experiment in this trial aimed at deterring 

 rodents from feeding on field-deployed wax/sugar caps 

 atop wooden PTS. Up to and during the 2000 field 

 season, we tested chemical additives (cayenne pepper 

 and bitter watermelon concentrate) for their ability to 

 deter rodent feeding on caps. Field and laboratory data 

 from these trials concluded that bitter watermelon 

 extract (up to 5% concentration) had no rodent- 

 deterrent effect, while cayenne pepper (up to 10% 

 concentration) had only little deterrent effect. Further, 

 the negative impact of these additives on cap structural 

 integrity far outweighed the potential benefits of rodent 

 deterrence. Therefore, we determined that a physical 

 barrier must be integrated into the sphere/cap system 

 to bar rodents from reaching and damaging the 

 vulnerable wax/sugar caps. We constructed five types 

 of wire guards (all formed of 1/8-inch grid hardware 

 cloth) for wax/sugar caps atop wooden PTS: 1 ) bottom 

 guard only, 2) top guard only, 3) side guard only, 4) 

 reusable top/side guard combination, and 5) fixed top/ 



26 



Fruit Notes, Volume 66, 2001 



