TRAP DESIGNS FOR SPOTTED WING DROSOPHILA, WHAT HAVE WE LEARNED?
USDA ARS, Horticultural Crops Research Unit
Fig. 1. Multi-site study with 6-7 designs
Spotted wing drosophila, Drosophila suzukii, is an invasive vinegar fly that appeared in Oregon and Washington in 2009. Since then, it has cause substantial problems with fruit damage and increased costs of management. Monitoring traps are steadily being improved, baits are becoming more specific and attractive to this species. There is a wide range of physical designs of a trap for SWD, some of it commercialized, and others being custom-made. As of now, it would be hard to settle on one design, but trap options that have caught more SWD are presented below. Remember: if holes or mesh are on the side of a trap, leave a side portion intact for pouring out the liquid.
There have been some broad comparison of traps that give us an idea of what works well.
In a 16-site study done throughout North America (Fig. 1), the Haviland and Dreves trap overall caught more flies. When we compared the number of flies captured based on the entry area of the trap (2 holes, 10 holes, top mesh, larger side mesh), more flies were caught as the entry area increased. We would assume that the bait volatiles are stronger coming from traps with greater entry areas, and flies enter those traps more readily.
In a 4-site study, yellow dome traps (Fig. 2) consistently caught more SWD than local traps that comprised of clear deli/cup container with holes. In this case, the dome trap differs greatly in many aspects from the cup trap in color, shape, entry area, orientation of entry area, etc. Also the dome traps used a greater bait volume than the cup traps.
There have been many follow-up studies looking at a specific feature of a trap while keeping other parts of the trap the same, this is to narrow down what features are important for catching SWD. Below is a generalized summary of some observed trends.
• Color- Traps that are red and/or black have caught more SWD than clear or white traps. Yellow sometimes works well, but it depends on the hue. The study that found yellow to work used a more orange “school bus” yellow.
• Bait volume – Traps that can hold greater bait volume have caught more SWD. More bait means more attractive substance—makes sense.
• Bait surface area – Traps that have greater bait surface area catch more SWD. This feature would be limited by size of the trap. As traps get too big, they are harder to hang in the canopy, and more likely to tip.
• Entry area – As entry area increases in a trap, more SWD are captured. However, this may be counterproductive as the area gets too large. At a certain point, the bait may volatilize too quickly or SWD are more likely to escape from the trap.
• Headspace – distance between the bait and the entry point on the trap (Fig. 3). In some studies but not all, as headspace decreases in a trap, more flies are caught. There are practical considerations, if the headspace is too small, the bait might spill out easily.
• Orientation of entry point – In one study, traps with mesh sides caught more SWD than traps with mesh on the lid. In another study, a trap with holes on the lid under a close-fitting cover caught more SWD than a trap with holes on the side.
• Preventing escape – Addition of soap to some of the baits, like apple cider vinegar, may help catch more SWD. Soap may not be helpful with baits like yeast-sugar-water, as it is a broth of living organisms. Dome traps are thought to work well because it may be more difficult for SWD to escape from the trap.
Basoalto et al. 2013. Factors affecting the efficacy of a vinegar trap for Drosophila suzukii. Journal of Applied Entomology 137: 561-570.
Cha et al. 2013. Comparison of a synthetic chemical lure and standard fermented baits for trapping Drosophila suzukii. Environmental Entomology 1052-1060.
Iglesias et al. 2014. Effect of trap design, bait type, and age on captures of Drosophila suzukii in berry crops. Journal of Economic Entomology 107: 1508-1518.
Lee et al. 2012. Evaluation of monitoring traps for Drosophila suzukii in North America. Journal of Economic Entomology 105: 1350-1357.
Lee et al. 2013. Trap design for monitoring Drosophila suzukii. Environmental Entomology 42: 1348-1355.
Renkema et al. 2014. Optimizing trap design and trapping protocls for Drosophila suzukii. Journal of Economic Entomology 107: 2107-2118.
Figure 2. Dome trap
Figure 3. Trap features