Soybean Stem Borers: Distribution, Seasonal Activity, and Sampling Methods for Improved Management

Impact on Soybean Production and Value

Improved knowledge of adult seasonal occurrence and field distribution, timing of egg laying, and development of accurate adult sampling techniques will contribute to improved strategies to control Dectes in soybeans.

Robert Wright (2014)

Key Ideas and Terminology

Fecundity refers to the reproductive rate of an organism

Study Objectives

To understand the distribution and seasonal activity of Dectes soybean stem borer (DSB) in Nebraska and develop sampling methods for improved management.


Field studies were conducted in 2013 and 2014 to describe DSB adult emergence, ovipositional period and densities in soybean fields. Both years, DSB emergence occurred at about 1250 degree-days (50° F base accumulated from January 1). Female DSB beetles reached peak fecundity during the 2nd and 3rd weeks after emergence. DSB densities in soybean field peaked during mid-July, after a majority of DSB adults have emerged.

Field studies were conducted during 2013 and 2014 to develop a cost effective sampling plan for monitoring adult DSB activity. Sticky traps, drop cloths and sweep nets were tested as potential sampling methods. Sweep net sampling was found to be a superior method while sticky traps and drop cloths resulted in low beetle counts.

Efficient sweep net sampling schemes were developed for minimizing the cost required to achieve a given precision level. A plan consisting of 2 samples of 150 sweeps each was developed to minimize the field costs for a desired precision level of 0.25.

These results indicate that monitoring for DSB in Nebraska should consist of a sweep net sampling plan with small sample sizes of large sampling units greater than 100 sweeps. Monitoring should be conducted throughout the month of July. Therapeutic actions should be timed after a majority of DSB adults have emerged and migrated into soybean fields, usually between 1400 and 2000 degree-days. Monitoring for adults in soybean fields with a history of DSB infestation may help improve the timing of such actions.