Entomology, Department of


Date of this Version



A Thesis Presented to the Faculty of the Graduate College at the University of Nebraska in Partial Fulfillment of Requirements for the Degree of Master of Science, Major: Entomology, Under the Supervision of Professor Robert J. Wright. Lincoln, Nebraska: May, 2015

Copyright Zachary Rystrom 2015


The Dectes stem borer, Dectes texanus Leconte, has caused significant economic damage to soybean fields in south central Nebraska during recent years. Most economic injury occurs when soybean plants become susceptible to late season lodging due to larval girdling. Developing a comprehensive management plan for Dectes stem borer in Nebraska is limited by lack of knowledge of seasonal activity and effective sampling plans to monitor adult populations. Field studies were conducted in 2013 and 2014 to describe Dectes stem borer adult emergence patterns, female ovipositional period and adult densities in soybean fields. Calendar date predictions for adult emergence varied, while degree-day predictions were similar across multiple years as the inflection point of both year’s emergence curves occurred near 1250 degree-days since January 1 (50° F. base). Female Dectes stem borer beetles reached peak fecundity during the second and third weeks after emergence and densities in soybean fields peaked during mid-July, after a majority of adults had emerged according to degree-day predictions. Field studies were conducted during 2013 and 2014 to develop a cost effective sampling plan for monitoring adult Dectes stem borer 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 to minimize the cost required to achieve a given precision level. A plan consisting of two samples of 150 sweeps each was developed to minimize the field costs for an acceptable precision level for making pest management decisions.

Advisor: Robert J. Wright