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The western corn rootworm, Diabrotica virgifera virgifera, is an insect pest of corn and population suppression with chemical insecticides is an important management tool. Traits conferring organophosphate insecticide resistance have increased in frequency amongst D. v. virgifera populations, resulting in the reduced efficacy in many corn-growing regions of the USA. We used comparative functional genomic and quantitative trait locus (QTL) mapping approaches to investigate the genetic basis of D. v. virgifera resistance to the organophosphate methyl-parathion. RNA from adult methyl-parathion resistant and susceptible adults was hybridized to 8331 microarray probes. The results predicted that 11 transcripts were significantly up-regulated in resistant phenotypes, with the most significant (fold increases ≥ 2.43) being an α-esterase-like transcript. Differential expression was validated only for the α-esterase (ST020027A20C03), with 11- to 13-fold greater expression in methyl-parathion resistant adults (P<0.05). Progeny with a segregating methylparathion resistance trait were obtained from a reciprocal backcross design. QTL analyses of high-throughput single nucleotide polymorphism genotype data predicted involvement of a single genome interval. These data suggest that a specific carboyxesterase may function in field-evolved corn rootworm resistance to organophosphates, even though direct linkage between the QTL and this locus could not be established. [ABSTRACT FROM AUTHOR]

Transgenic maize plants expressing ds RNA targeting western corn rootworm ( WCR, Diabrotica virgifera virgifera LeConte) v- ATPase subunit C mRNA for RNAi provided significant root protection from WCR larval feeding damage in greenhouse assays compared to negative controls. Transcribed hairpin ds RNA in WCR-resistant maize plants was present as both intact hairpin-derived ds RNA and plant-processed si RNA. Therefore, the ability of ds RNA and si RNA targeting Dv v- ATPase C mRNA to cause an RNAi response was studied in both WCR larvae and adults. In 9-day diet-based feeding assays, ds RNA of at least 60 bp in length resulted in high levels of larval mortality. In contrast, 15-, 25- or 27-bp ds RNAs or pooled 21-bp si RNAs did not cause mortality of exposed larvae. When larvae were fed with diet overlaid with si RNAs, Dv v- ATPase C transcript levels did not change. Conversely, when WCR larvae were fed with diet overlaid with 184-bp ds RNA, the mRNA level was reduced by >20-fold relative to yfp ds RNA negative control. Similarly, 184-bp ds RNA caused 100% mortality of WCR adults, whereas the mortality of adults fed on diet treated with si RNAs was similar to the negative control. Feeding adults with si RNAs on diet did not affect the level of Dv v- ATPase C mRNA transcripts, whereas adults fed with the 184-bp ds RNA showed approximately 35-fold reduction in the target mRNA level. Similar results were obtained with the WCR adults injected with 184-bp ds RNA or 21-bp si RNA. These results suggest that only long ds RNA or hairpin-derived ds RNA is effective in causing lethal knock-down of Dv v- ATPase C mRNA. These results have implications for efficacious plant-delivered ds RNA for the protection of transgenic maize from WCR feeding damage and for the risk assessment of transgenic maize expressing insecticidal ds RNA. [ABSTRACT FROM AUTHOR]