A Low-Cost Method of Trapping Out Apple Maggot Flies

Objectives and procedures

This project aimed to test an alternative to reusable wooden or plastic sphere traps for monitoring and trapping out apple maggots in their mature phase. A ½ acre block of Liberty apples was surrounded by traps, these being Gempler reusable wooden spheres coated with a sticky substance sold commercially as TangleTrap, and alternating with apples coated with the same substance. Synthetic apple odor bait (butyl hexanoate) was used with both trap types. Traps were set out the first week of July and checked weekly until mid-October, at which point the fruit were harvested. Tallies of weekly captures were kept for each type of trap, and the amount of time needed to maintain each type was recorded. Monitoring traps were hung in the center of the block, and 100 of the Liberty apples in the block were also examined on each visit for apple maggot fly stings, to ensure that the trap-out was working.

The Gempler traps were handled in the recommended manner; that is, each trap was coated with Tangletrap and hung using the plastic/wire loop hangers provided. Every three or four weeks the traps were cleaned of excess flies and debris, and re-stickied if necessary. At the end of the season, these traps were taken down, cleaned, and stored in boxes for the winter.

The apple traps were transfixed with a wire that pierced through the core and looped at the bottom. They were covered with TangleTrap and hung from the trees. When the apples had discolored or rotted to the extent that they would not be attractive to flies, they were removed and replaced with new traps. At the end of the season the remaining apple traps were disposed of in the trash.

Most of the apple traps used in this project were Romes, but there was a short period of time when Rome apples were unobtainable, and Red Delicious apples were used instead. There did appear to be a difference in longevity and usefulness between the two cultivars, as will be discussed below.

Results

The sphere traps and the apple traps captured similar numbers of apple maggot adults for most of the season; as can be seen from Table 1, in most weeks there was no significant difference in captures between the two types of traps. The two weeks in mid- to late August when the apple traps were significantly less effective than the sphere traps were the weeks when Red Delicious was substituted for Rome in most of the apple traps. We attribute the greater effectiveness of the Rome apples to their maintaining both integrity and color for several weeks (provided that the skin was intact). The Red Delicious seemed to turn brown almost immediately when covered with TangleTrap and exposed to heat and sunlight, even when the fruit were not pierced with the wire or otherwise injured. In his early trials, Dr. Ronald Prokopy of the University of Massachusetts discovered that this browning was very unattractive to the flies. We would like to run this trial again, using Romes only, in order to see whether our reasoning is correct, especially since the period when Red Delicious predominated coincided with the peak immigration of apple maggots into the block.

A minor advantage to the apple traps is the fact that they are considerably lighter than the sphere traps, weighing usually 6-7 ounces compared to 10 ounces for the sphere traps. This not only makes them easier to carry, but also facilitates positioning them in the tree; often the weight of the sphere trap will drag the branch on which it is hung several inches lower, either immediately or over the course of several weeks. This did not seem to occur with the apple traps, making it much easier to find a favorable trap position.

No apple maggot fly injury to fruit was seen at any time during the summer, nor was any noted by the pickers at harvest time. Sphere traps positioned in the middle of the block caught only a few flies over the course of the season, indicating that the trap-out using the combination of sphere traps and apple traps was successful.

Table 1. Weekly trap capture averages

Week Sphere Traps Apple Traps
7/9 0 0
7/16 0 0
7/22 0.16 0.16
7/29 0.22 0.39
8/5 2.17 1.28
8/12 1.77 1.61
8/19 2.11 0.78
8/26 1.39 0.17
9/2 1.16 1.11
9/9 0.94 1.47
9/16 1.00 0.50
9/23 0.59 0.47
9/30 0.44 0.78
10/7 0.16 0.26

Economic analysis

Among the motivations for this project was the high cost of the reusable traps, and their substantial maintenance requirement, post-season cleaning being the major item. Thus, we kept careful track of time and expense per trap, for both the apple traps and the sphere traps. Table 2 shows that, on the whole, the apple traps were somewhat more cost-effective. The apple traps were definitely much less expensive to buy, even considering that they had to be replaced three times, on average, in the course of the season. The TangleTrap could be applied a little more quickly to the spheres, because of their regular surfaces. The sphere traps did not need to be replaced, but cleaning them, both during and after the season, was extremely time consuming.

Table 2. Cost and labor for preparing sphere traps and apple traps

Sphere traps Apple traps
Cost per trap $3.65 $0.20 (x3=$0.60, to be comparable)

Applying TangleTrap 36 seconds 40 seconds
Preparation 0 8
Replacement 0 48 (x3=144 secs.)
Cleaning 60 0
Disposal/final cleaning 132 5
Total time 228 seconds 197 seconds

The bulk of the time consumed with the apple traps was in the multiple replacements needed over the course of the season. (As might be expected, traps deteriorated rapidly in the hot weather in late July, and much less quickly in the cooler weather later in the season.) It might be possible to further streamline the replacement process. The replacement apple traps were prepared on the spot each week; it may well be more efficient to prepare a large quantity of apples once, and draw from the supply as needed. The sphere traps, on the other hand, have been in use for over twenty years, and their cleaning and maintenance by now are probably as efficient as they are going to get.

Thus the time savings of ½ minute per trap of the apple traps over the sphere traps might be increased with more experience in handling them. But even ½ minute per trap could be significant when one is using several hundred, as would be typical in an orchard trap-out program.

Discussion

Overall the results of this project were very encouraging. The trap-out worked well, and the apple traps held up relatively well (even in the hottest part of the summer most of the apples lasted two or three weeks) and seemed to be comparable in effectiveness to the reusable sphere traps. If the apple traps are indeed equal to the sphere traps in effectiveness, they represent a viable, cost- and time-efficient way to trap out apple maggot adults without the use of insecticides.