Percent nitrogen-15 excess in elytra and head capsules of western corn rootworms fed as adults on labeled and unlabeled transgenic maize
Mean atom % N15 excess in elytra and head capsules of field-collected D. virgifera virgifera confined for 72 hours on N15 labeled and unlabeled maize (Z. mays L.) plants under various refuge treatments in La Porte (A) and Tippecanoe (B) Counties, Indiana (July 2015). Beetles were caged in pairs on either leaves, tassels or silk of known labeled and unlabeled plants and allowed to feed freely. Cages were custom made bags of mesh cloth measuring 30.48 x 76.2 cm and secured with large binder clips. Cages were placed over silk and leaves together when the ear of corn was not fully developed. Beetles were caged on non-labeled plants to confirm that there was (1) no enrichment in unlabeled plants and (2) no cross-contamination during testing. Beetles were collected following 72 hours and processed for mass spectrometry as described hereinabove. Beetles used for this experiment were collected from natural populations at the Agronomy Center for Research and Education in Tippecanoe Co., IN, a location approximately 15 miles from test plots. Beetles were confined to plants within 24 hours of collection. This experiment was conducted July 21-23 at TPAC and July 29-31 at PPAC during peak times of adult rootworm activity. Uneven sample size between locations resulted from fewer beetles being collected on July 21; uneven sample size for plants resulted from individual beetles escaping cages. When the number of beetles was limited, labeled plants were given priority over un-labeled plants because %N15 excess values in these samples were needed to determine baselines (value above which a beetle is determined to be “labeled” from larval feeding). Only beetles from labeled plants in La Porte County contained a mean atom % N15 excess in quantities sufficient to be defined as “labeled” in 2013 study (in bold).