Sampling for brown marmorated stink bug (Halyomorpha halys) in soybeans: a new visual plant inspection method

Sampling soybean fields for brown marmorated stink bug (BMSB), Halyomorpha halys Stål (Hemiptera:  Pentatomidae), has proven to be a challenge. Both adults and nymphs have a strong ‘startle response’ and drop to the ground with even the slightest disturbance.  This could reduce the effectiveness of the traditional sweep net and ground cloth sampling methods.  In 2013 and 2014 in Virginia, Delaware and Maryland, we evaluated a visual plant inspection method by comparing numbers observed to numbers caught using a sweep net.   The visual inspection method consisted of counting BMSB seen on the plants in a 2-minute long inspection period while walking carefully down and between two rows. The ends of each sample area were marked with flags.  After a 30-minute interval, which allowed the stink bugs to reposition in the canopy, each flagged area was sampled using 15 sweeps with a 15-inch diameter sweep net. Regression analyses compared the numbers seen vs swept—by state/year and combined. Using these regressions and setting the number swept to 5 per 15 sweeps (the current economic threshold for Virginia) indicated that overall, there is a reasonably close relationship between the numbers sampled by the two methods. The best result was seen when data from all states and years were combined (76 fields, 2,042 paired comparisons) and showed that 5.4 BMSB were observed in 2 minutes when at the 5 per 15 sweep threshold (Y=0.984x + 0.4359, R²=0.6934).  Visual inspection appears to be an effective method for assessing BMSB populations in soybean.