Within field spatial distribution of Dectes texanus (Coleoptera: Cerambycidae) in Kansas soybean (Glycine max)

The soybean stem borer, Dectes texanus, is a species native to North America that has recently become an important pest in soybean, Glycine max. Monitoring adult activity within fields is important in order to understand the distribution of larvae in a field and for effective chemical applications to target adults. The objective of this study was to examine the within-field spatial distribution of adult D. texanus in several individual soybean fields found throughout central Kansas. Soybean fields were scouted at the beginning of adult activity (late June to early July) during 2010 and 2011. Eleven fields were infested with D. texanus and were used for modeling the spatial distribution of adults across a production soybean field. Geostatistical software was used to produce sampling grids (1 to 165 points per field) for all fields. Fields were sampled using sweep nets by performing 20 sweeps in each cardinal direction for a given waypoint on the sample grid. Semivariograms were calculated to model the change in spatial correlation with increasing distance between samples. Spatial distribution of larval damage during 2010-2011 was best described using a spherical and exponential models. Preliminary results suggest that there is great variation between individual fields and year depending on previous and current surrounding crop types. Higher densities of adult D. texanus may depend heavily on where the previous years soybean crops were planted. Implications from these results on current management strategies will be discussed.