Landscape effects on spatial distribution and movement of brown marmorated stink bug in peach orchards
The spatial patterns of the brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), in peach orchards was investigated in the summer of 2013. Seven orchards across four farms were monitored weekly for H. halys from May through September. These orchards were chosen based on data from the previous year indicating presence of high numbers of H. halys at these sites. Portions of the area surrounding these orchards were also monitored These areas consisted of other peach orchards, ornamentals and apple trees. Assessments for damage were conducted as peaches ripened. These consisted of visual assessments for stings and catfacing damage. Peaches were peeled to assess and compare damage with and without the peel. ArcMap was used to visually display H. halys populations in each orchard, and analyze the data to determine clustering, spatial autocorrelation and influences of abiotic and landscape factors. Thus far, clustering statistics for two sites has been calculated, as the analysis is still underway. Significant clustering was found at the two sites for most sampling dates.
• In 2013, four orchards at two farms in northern New Jersey and three orchards at two farms in southern New Jersey were selected for monitoring. Sampling in the previous year indicated low to nonexistent populations in many of the orchards sampled across the state in both northern and southern New Jersey. These orchards were selected for monitoring based on the high numbers of H. halys found in 2012.
• Two of the farms were Rutgers research stations, one in northern (Cream Ridge) and one in southern (RAREC) New Jersey. The other two farms were commercially managed farms, one in northern and one in southern New Jersey. For the purposes of this report, I will refer to the farms as Cream Ridge, RAREC, Farm N (northern), and Farm S (southern).
• Populations varied widely among orchards, independent of location. Overall, low H. halys populations were observed at six orchards with 150 total counts (nymphs and adults) each sample date, while at orchard 2 in RAREC, populations were very high, with counts around 1,000 on each sample date (Figure 1). At Farm N, because orchard 2 had a total of 14 H. halys across the season, the data were not plotted.
• Peak population dates varied significantly in different orchards. At Cream Ridge, populations peaked in August, while in other orchards populations peaked in May or June. This was most likely due to the initiation of spray regimes.
• Landscape features and outside factors such as spray regime and their contribution to population totals in the field will be analyzed using principal component analysis and a conditionally autoregressive model.
• Sampled trees in the seven orchards are being georeferenced in ArcMap and displayed on maps.
• Clustering of H. halys was analyzed using the Ripley’s K statistic.
• Orchard 1 at Cream Ridge and orchard 2 at RAREC have been mapped and analyzed. Because there are too many maps to display, selected maps and analyses are displayed in Figure 2.
• Damage to fruit was assessed in 2013. Each orchard was sampled to evaluate the number of externally damaged, undamaged, and catfaced fruit using visual counts. These data will be displayed visually on a map and correlated using cokriging.
• Damage levels varied widely among fields. At Cream Ridge, 1.5% of sampled peaches showed damage. At RAREC, 25.5% showed damage. At Farm N, 0.5% showed damage. At Farm S, 1.4% showed damage.
• In August at Cream Ridge, 10 fruit per tree were picked and peeled to assess damage found on the exterior of the fruit before and after peeling. To do this, the number of stings per fruit was counted on the outside and inside. Ripeness of the fruit and whether or not the fruit was catfaced was also recorded.
• Data have been inputted and will be displayed on a map using ArcMap. Damage levels will be correlated with numbers of nymphs and adults using cokriging. The contribution of abiotic and landscape features to damage will be analyzed using principal component analysis and a conditionally autoregressive model.
• The area surrounding the sampled orchards was monitored for H. halys. There were at least 100 sample points in each of these additional areas, whether north, south, east or west of the orchard.
• Data have been inputted but has been neither mapped nor analyzed. Inverse distance weighting and kriging will be used to estimate populations outside of these sampled areas to see if they could contribute a significant amount of individuals to each other as well as the sampled orchard.
Field sites monitored in 2013 were selected from farms monitored in 2012 that had high populations of H. halys. All orchards either participated in the Rutgers fruit IPM program or Rutgers agricultural research stations. Specific orchards sampled known to harbor populations of H. halys. Prior to sampling, land use around orchards was assessed to ensure that land use type was different between orchards.
Orchards were surveyed weekly for eggs, nymphs, and adults using visual and beat sampling from May through August except for RAREC orchard 2. Monitoring in RAREC orchard 2 was started in July because of the very high numbers of H. halys found and the drop in numbers in other orchards. An issue during the previous 2012 field season was the frequent use of pesticides. With the large number of sites, it was difficult to juggle sampling dates around multiple spray schedules. The smaller number of farms visited each week in 2013 made it easier to visit the farms on a regular weekly schedule. A smaller number of farms were also visited in 2013 because sampling efforts in individual orchards was significantly increased. In 2012, each orchard visited had 20 sample points. In 2013, each orchard had from 100 to 500 sample points. With the additional sampling in neighboring areas, this significantly increased the time spent at each farm.
In comparison to data from 2012, H. halys populations in most orchards remained low or even dropped in numbers. This may have been due to the increased uses of pesticide control in 2012 and 2013. However, the newly sampled orchard, orchard 2 in RAREC, had much higher populations than all other sampled orchards. The reasons behind this are unknown at this time, but visual assessment of aerial photography indicates possible contribution of individuals from a wooded edge. It is also likely that the impact of Hurricanes Sandy and Irene may have had a significant impact on variations of populations; natural habitat harboring H. halys could have been disrupted by these natural weather patterns.
For objectives 2 and 4, the increased sampling effort in multiple orchards improved my ability to answer these objectives. Every tree in the seven orchards was sampled, ranging from 100 trees to almost 500 trees, in addition to surrounding areas, each with 100 or more sampling points. This data set will allow me to show clustering in each field, and will allow for more accurate interpolation of unsampled points further from the orchard. Associations with landscape features will be more easily drawn from this data set. From personal communication with other stink bug researchers, mark-and-release studies with captured individuals of stink bugs were not very effective, whereas marking in situ resulted in a better return rate of individuals. In 2013, not enough adults were found to mark individuals in situ to assess how they move around a field. This will be done in 2014 in sites confirmed to have a consistent weekly population of at least 50 adults.
Damage assessments for objective 3 were completed in 2013. This consisted of visual assessments for damaged, undamaged, and catfaced peaches in each orchard in addition to fruit peeling to assess damage outside and underneath the peel. Preliminary examination of these data shows damage to vary widely among the orchards, from 0.5% damage in Farm N to 25.5% damage in RAREC. In 2014, a larger number of fruit will be sampled, and at two separate sample dates.
Impacts and Contributions/Outcomes
All data have been recorded and inputted into a database. However, much of the analysis remains to be undertaken. Similar to 2012, low populations throughout the orchards make it difficult to draw conclusions about the spatial arrangement of populations, as low populations may behave differently than high populations. However, the one orchard with high populations will allow comparison of clustering and contribution from landscape factors between high population and low population samples. Visual assessments of aerial photography already indicate that forested areas may contribute individuals to high population orchards. Both low and high populations of H. halys exhibit clustering, but the factors affecting this have not been examined.
Focused insecticidal control used by growers, especially prudent management with border sprays of areas surrounding orchards and targeting key host plants, has been a more common practice among growers I work with. This is an indication that more information about where H. halys are immigrating from and to will be useful to growers in the future.
This research was presented at the Entomological Society of America meeting in Austin, TX in November 2013.
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