The purpose of this study was to improve sampling techniques for the brown marmorated stink bug in peach orchards. This research focused on the standardization of visual sampling techniques, specifically with the importance of time of day and the impact of different observers. Work was conducted over the summer of 2013 and 2014 in two orchards in south and central New Jersey. To evaluate daily photoperiod as a variable, orchards were sampled at 0, 2, 4, 7, 10, 12, 15, 18, and 21 hours past sunrise. The results indicated that observable populations of BMSB change dramatically over the course of a 24 hours period. Nymphs and adults have different behavioral patterns. Nymphs are much more prevalent during the afternoon but decrease in number during the morning and evening. Adults have relatively constant population levels over the diel period but increase slightly at night. The ratio of adults to nymphs in an orchard is not consistent over the course of a growing season, nor between sites at the same time of the growing season, nor at a site between years. Differing observers did not have a significant effect on the number of BMSB observed, supporting the hypothesis than visual counts are comparable between different observers. The findings of this study provide strong evidence for the need to hold time of day constant when visually monitoring BMSB populations in peach orchards over the course of a growing season.
Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), commonly known as the brown marmorated stink bug (BMSB), is an invasive stink bug that has been spreading across North America since the mid 1990s (Hoebeke & Carter, 2003). BMSB has quickly become a serious pest in many cropping systems such as soybean, pear, cherry, apple, peach, grapes, peppers, tomatoes, eggplant, corn, okra, pecans, hazelnuts, and caneberries (Nielsen et al., 2011; Nielsen & Hamilton, 2009; Lee et al., 2013; Basnet et al., 2014; Kuhar et al., 2012; Sutherland & Bundy, 2012; Hedstrom et al., 2014). Currently, BMSB monitoring is done using timed visual counts, beat sheet sampling, sweep net sampling, black-light sampling, and pheromone trapping (Lee et al., 2013; Leskey et al., 2012). These techniques are used to assess population growth in a field over the course of a summer or to compare population densities between geographic areas. The focus of this research was to determine the comparability of timed visual counts taken at different times of day. This is important information for growers to have if they want to effectively use this monitoring method.
There were four project objectives:
- Determine relative attractiveness of different color lights to BMSB.
- Determine the best time of day to sample for BMSB in peach orchards.
- Determine BMSB population density within peach orchards over a 24 hour period throughout the growing season.
- Create a standardized protocol for visual sampling of BMSB.
Objective 1 was done by conducting a laboratory study in the Rutgers University Entomology Department. All BMSB studies were conducted using individuals maintained in a colony in the Hamilton laboratory. Individuals were reared under standard conditions (Nielson et al., 2008). A test chamber for the light trial was constructed in the basement of Blake Hall at Rutgers University. A room with dimensions of 1x2x2meters was modified to fit the needs of the experiment. The walls, floor and ceiling were gridded into 0.3m squares using 2.54cm black electrical tape (3M, St. Paul, MN), creating 254 grid cells. A light socket (3M, St. Paul, MN) was affixed to the center of four grid cells on one wall and then the average distance from each grid cell was calculated. The grid cells were then grouped by their average distance into 16 distance categories by rounding the average distances to the nearest 0.1 meters. (0.2m, 0.5m, 0.6m, 0.8m, 0.9m, 1.0m, 1.1m, 1.2m, 1.3m, 1.4m, 1.5m, 1.6m, 1.7m, 1.8m, 1.9m, 2.0m, and 2.1m). For each trial, twenty five mixed sex adult stink bugs were released at the same time on the floor. Insects were released by gently shaking out their holding container on to the floor in the center back wall grid intersection, 1.76 meters from the light source. Each trial was run for 30 minutes. A light bulb (Brightech International, Somerset, NJ) of a determined wavelength (560nm-green, 590nm-yellow, 750nm-red, 460nm-blue, and 640nm-orange) was selected for each trial as the light source The selected bulb was screwed into the mounted socket and left on for the duration of the trial. No other light sources were on or visible in the room during trials. Control trials were done as dark (no light) trials. Once 30 minutes had elapsed, the trial was stopped and the door to the room was opened. The grid position of each stink bug was then recorded. As each stinkbug was recovered, it was placed into a container to avoid confusion as the rest were recovered.
After each trial was completed, the room was aired out with a large fan for 5 minutes to help reduce the risk of stink bug aggregation pheromone buildup on previously visited grid cells. Individual stink bugs were not used in trials more than once a day. All stink bugs were placed back into the colony at the end of the day so that each day, a new randomly selected set of 25 individuals were used in trials.
All trials were replicated seven times. Individuals were grouped into distance categories for analysis. For each trial, a histogram was created for the number of individuals per distance group. These data distributions were then compared to the control distribution to see if significant differences in distribution could be detected by using a Kruskal-Wallis Sum Test.
Objectives 2, 3, and 4 were done following a weekly protocol using peach orchards maintained at two locations in New Jersey: the Rutgers Agricultural Research and Extension Center in Bridgeton, NJ and the Rutgers Fruit and Ornamental Research Extension Center in Cream Ridge, NJ. At each location, 132 trees spread over 6 rows were monitored using timed visual counts at 9 different intervals throughout the day. These intervals were standardized by sunrise to avoid problems with early versus late season comparability. The sampling times were sunrise plus 0 hours, 2, 4, 7, 10, 12, 15, 18, and 21 hours. The normal 3 hour intervals were reduced to two hours near sunrise and sunset to provide greater model resolution at these times.
Two minute visual surveys of each tree were done by walking around the tree in a manner that allowed maximal viewing of all BMSB hiding/resting/feeding locations. The number of observed BMSB was recorded at the conclusion of each two minute period. BMSB counts were recorded as: BMSB adults, small nymphs (2nd and 3rd instars), large nymphs (4th and 5th instars), nymphs on an egg mass (1st instar), and unhatched egg masses. Data were analyzed using a Pairwise Wilcox Rank Sum Test in R 3.1.1.
The null hypothesis of this experiment was that all counts from the different times of day would be the same. The alternative hypothesis was that sampling at different times throughout the day would result in different amounts of observed BMSB.
The investigation into how different light sources effect BMSB is still underway as the protocol was expanded to address a broader range of factors. The findings for adults showed that all light colors tested were attractive to BMSB. Figure 1 shows the average distance that adults were found from the light fixture after a 30 minute exposure in the test room. All colors and the control represent the average of seven trials of 25 mixed sex BMSB. This study was expanded to determine BMSB’s minimum threshold of light detection at varying wavelengths, if different life stages are impacted differentially, and how important time of light exposure is to the resulting distribution of individuals around the light.
The findings from objects 2 and 3 are complete and are currently being written up for publication. In this study, the time that sampling occurred at, location, and year had a significant effect on the number of BMSB observed. Figure 2 shows how the observed average number of nymphs per tree (A) changes dramatically over the course of a 24 hours period whereas the number of adults per tree (B) is fairly stable. The largest proportion of the population from July through August was made up of nymphs, which outnumber the adults be a factor of ~10 as shown on the y-axis.
These data are representative of the pattern seen at both sites across both years of the study. The findings of this study provide strong evidence that visual sampling must incorporate a standard time of day when observations are to be made.
The results of this work have been presented at both national and local meetings. Preliminary findings ere presented at the 2014 Entomology Society of America (ESA) Eastern Branch Meeting and the 2014 ESA National Meeting. The final results of this project will be presented at the 2015 ESA Eastern Branch Meeting. This work was also presented to growers, pest scouting program managers, and researching at the December 2015 BMSB Working Group Meeting.
Education & Outreach Activities and Participation Summary
This work will lead to two publications. The first will include objectives 2, 3, and 4. The second will include objective 1. An additional publication is planned detailing the light based study that is an extension of objective 1. This study is on-going and will be completed by the end of August 2015. The paper on objectives 2, 3, and 4 is currently being edited for submission to the Proceeding of the National Academy of Science.
The findings of this work will continue to be disseminated through outreach events over the next several years.
The monetary saving this work will lead to will be in the form of reduced crop loss and pesticide application due to more accurate population monitoring of orchard BMSB levels. No work has currently been done to quantify the impact of BMSB in peaches in New Jersey so hard data to support or disprove this outcome is not available at this time.
This research will be incorporated into sampling techniques by IPM scouts and growers. The results of this study have been shared with farmers, researches, and scouting program managers throughout the area’s affected by H. halys at the BMSB Working Group meetings.
Areas needing additional study
This study highlights the need to investigate diel behaviors of insects that can affect monitoring outcomes. Many insects have been shown to feed at different rates depending on the time of day. If visual sampling is being used to monitor them, those counts will need to be standardized in the same way that we have demonstrated for BMSB.