Multivariate and ecological approach to assess non-target effects of Bt rootworm maize on ground beetles (Carabidae)

We conducted a non-target field study that was both a practical assessment of the potential treatment effects of rootworm Bt maize and an ecological investigation of how several environmental variables may affect ground beetle assemblages. We then examined how the environmental variables influenced the treatment effects. Carabid beetles and other arthropods were sampled with pitfall traps in 60×60 foot (18.3×18.3 m) plots.  The experimental treatments included Herculex® RW rootworm-resistant Bt maize (event DAS-59122-7, Cry34/35Ab1) and its corresponding non-Bt isoline.  Within both of these Bt treatments were three insecticide subtreatments (all applied at labeled rates): check, seed treatment (clothianidin, Poncho® 1250), and granular soil insecticide treatment (tefluthrin, Force® 3G) to serve as a positive control and to assess the relative strength of the effects of Bt and insecticide.  Data were analyzed with canonical correspondence analysis.  Overall, insecticide effects on arthropods were significantly greater than Bt maize; and no significant biological effects were observed between Bt maize and isoline controls.  Our most substantial finding was that insecticide treatment effects were small compared with ecological and environmental factors such as beetle phenology, elevation and prey availability.  Considering such environmental factors may help account for the natural variation that makes running ecological field studies so challenging.