Distribution of rotation resistance in eastern Iowa and effects of soybean varieties on survival and fecundity of Diabrotica virgifera virgifera LeConte

The western corn rootworm Diabrotica virgifera virgifera LeConte (WCR) and the northern corn rootworm Diabrotica barberi Smith & Lawrence (NCR) are two significant insect pests of corn in North America. Both species have adapted to crop rotation in the Midwest, NCR through extended diapause and WCR by ovipositing in alternative crops. We conducted surveys during 2008 and 2009 to collect data on the presence of rotation-resistant NCR and WCR. Data were collected by placing Pherocon AM sticky traps in soybean and corn fields and by placing emergence cages in corn fields. Rotation-resistant WCR was most common in the northeastern and east-central Iowa, although no populations were above the economic threshold. Rotation-resistant NCR was found throughout eastern Iowa, the majority captured in the north-central and south-central regions. In 2009 a laboratory study was conducted to test whether soybean varieties with varying resistance to soybean aphid Aphis glycines affected survival and fecundity of several WCR strains. Soybean varieties included lines with resistance genes rag1 and rag1/rag3 as well as a near isoline that lacked rag1 or rag1/rag3. All WCR strains displayed similar longevity, fecundity, and consumption of leaf tissue across the soybean lines tested. We interpret the results of our laboratory study to indicate that soybean varieties with rag1 and rag1/rag3 resistance to A. glycines are selectively neutral for rotation-resistance trait in WCR.