Selection and genetic analysis of European corn borer (Ostrinia nubilalis): Plant abandonment vs. plant establishment
Aaron J. Gassmann
In a selection experiment, we tested whether plant establishment and plant abandonment are heritable traits for the European corn borer, Ostrinia nubilalis. Emerging egg masses were placed on non-Bt corn plants and silking individuals (Silkers) were collected every 15 minutes during a four hour period. Plants were dissected 24 hours later and established individuals (non-Silkers) were collected. These two phenotypes were reared to adulthood separately and mated with a like phenotype. Selection over subsequent generations of the Silker colony showed an increased propensity to abandon the host plant (parental generation 3.12%, 6th generation 38.00%). Selection of the non-Silker colony did not show a consistent trend in plant establishment but was significantly different from the Silker colony at the 6th generation (non-Silker 12.57%, Silker 4.61%).
We used video tracking software (EthoVision) to quantify behavioral differences between the Silker and non-Silker colonies. Individual neonates (Silker, non-Silker, and wild type) where put in 1cm diameter cointainers and placed beneath an infrared camera connected to a computer and recorded for 20 minutes. Quantification of behavior variables did not result in significant differences between colonies.
Additionally, we investigated differences in candidate genes in O. nubilalis (foraging, shaker, and slowmo) to better understand the genetic mechanisms underlying host plant abandonment. We used quantitative real time (qRT) PCR to determine expression profiles for these genes. Eggs samples from Silking, non-Silking, and a non-selected lab colony were collected at 0, 24, 48, 72, and 96 hours after egg deposition. Also, 1st instars exposed to corn tissue for 4 hours were collected (to mimic conditions of the selection experiment). Expression of foraging and slowmo show significantly higher expression in the Silking colony compared to the non-Silking and non-selected lab colony at the 0 hour time period. As foraging encodes a cGMP dependent protein kinase (PKG) it may affect downstream pathways that could influence behavior.