The monitoring protocol described here can serve as an essential part of research on CBB and control strategies against this invasive coffee pest. We have put this monitoring protocol into practice over the 2016 and 2017 coffee growing seasons on Hawaii Island in an effort to optimize every step of the process outlined in this article and the accompanying video. By doing this, we have ensured that important aspects of CBB population dynamics have been monitored and quantified, that the most effective low-cost materials have been determined for each step of the protocol, and that the data collected on CBB movement, infestation, mortality, coffee plant phenology, weather and farm management can be used to inform and improve current control strategies.
There are a number of critical steps in this protocol that must be followed to ensure optimum results. First, funnel traps must be set up at a uniform height and positioned between trees. This will ensure that the attractant is sufficiently diffused through the air, and that beetles can access the trap from all directions. Second, it is necessary to use sieves with the same mesh size (coarse-mesh sieve ≈ 1.5 mm, and fine-mesh sieve ≈ 1.0 mm) throughout the duration of monitoring to ensure consistent results for volumetric estimates of CBB. Third, the proportion of CBB versus other beetles in each trap can vary considerably among traps and over the growing season, and it is therefore necessary to estimate these proportions to minimize noise in trap count data. Fourth, infested berries must be stored in a cooler on ice until they can be transported to the lab, after which berries should be stored at 14 °C until dissection. Storage in a humid environment will result in CBB emergence from the berries20. Lastly, dissections must be conducted within 1 - 3 days of collection to ensure maximum survivorship of CBB. Mortality of CBB may occur if berries are stored at cold temperatures for prolonged periods.
Additional steps may be required for research initiatives that are not included here (e.g., monitoring CBB predator abundance). Modifications may also be made to this protocol if time, resources, and/or equipment are limiting factors. The trap attractant comprised of 3:1 methanol:ethanol may be changed to a 1:1 methanol:ethanol solution with comparable results21. Soapy water may also be substituted for propylene glycol as a kill solution in traps22. For estimates of large numbers of CBB (e.g., more than several hundred per trap), mass-based estimates of CBB may be substituted in place of volumetric estimates. For example, the average dry weight of a single CBB may be determined using a high-resolution scale. CBB collected in 70% ethanol may then be dried in an oven, and weighed to estimate the number of CBB per trap. A modified volumetric estimate can also be made by putting all the CBB from a trap into a graduated cylinder along with the kill solution, and allowing the contents to settle to the bottom22. Once settled, the volume of the cylinder filled by CBB may be noted, and the conversion factor for 1 mL may be determined to estimate the total number of CBB caught per trap. Lastly, coffee growers that have an intimate knowledge of their farms and are using this monitoring protocol to estimate CBB infestation and movement may wish to omit steps that involve documenting phenology and counting the number of raisins on branches.
Two potential limitations of this protocol are worth mentioning here. First, sampling of branches at chest height does not capture infestation in the early-flowering crop that may start higher in the tree canopy. However, the observations suggest that this early-flowering crop accounts for a very small percentage of the overall yield in coffee farms in Hawaii. Second, our protocol only accounts for infestation in green berries, and thus may not accurately capture estimates of berry damage when the number of color break and ripe berries is high (September - December in Hawaii).
The CBB monitoring protocol presented here has several distinct advantages over other monitoring protocols that are currently in use. First, the systematic random sampling design allows for more even sampling relative to sampling done in a zig-zag pattern. This sampling design allows for better estimates of berry damage throughout a given field, and increases the potential to detect hotspots. Second, the inclusion of elements in the monitoring protocol that are essential to coffee agroecosystems (e.g., phenology, weather variables, and management practices) will improve our understanding of the dynamics between invasive insect pests, their host plants, and various environmental factors. Third, the use of a mobile electronic data collection application during field surveys permits real-time data to be quickly and efficiently entered and organized into a database, and can also be related to other automated coffee monitoring methods such as detection via remote sensing23. Another important benefit of this method of data collection is that detailed infestation reports may be generated with ease, allowing timely management recommendations to be relayed to growers. Lastly, the real-time data collected on CBB biology, coffee plant phenology, weather, and management can be incorporated into the development of predictive models that can be used to customize management plans for a particular coffee growing location.