Quantitative trait locus mapping and functional genomics of an organophosphate resistance trait in the western corn rootworm, Diabrotica virgifera virgifera.

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 methyl-parathion 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.

Categories of resistance in St. Augustinegrass lines to southern chinch bug (Hemiptera: Blissidae).

The southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), is the most important insect pest of St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, in Florida and other Gulf Coast states. Resistance to southern chinch bug was identified previously in St. Augustinegrass lines 'FX-10' and NUF-76. Choice and no-choice tests and ovipositional and developmental studies were conducted to determine the categories of resistance in FX-10 and NUF-76 to southern chinch bug. When adult chinch bugs had a choice among attached stolons of three susceptible lines ('Floratam', 'Bitter Blue', and 'Palmetto') and the two resistant lines, chinch bugs were found significantly more often over a 5-d period on the susceptible lines. This result indicates the presence of antixenosis in the resistant lines FX-10 and NUF-76. In a no-choice study, chinch bugs produced less than half as many excretory spots on FX-10 as on the susceptible lines. Significantly fewer excretory spots produced by chinch bugs confined on NUF-76 accumulated by days 3 and 5 after release; however, on the first 2 d, the accumulative number of excretory spots was not significantly less than that found on susceptible lines. The no-choice study confirmed a high level of antixenosis in FX-10, a moderate level of antixenosis in NUF-76, and possible antibiosis in NUF-76. Ovipositional and developmental studies were conducted using only Floratam (a widely planted cultivar that was formerly resistant to B. insularis) and the two resistant lines. Adults released on Floratam produced 11 and 5 times more eggs and 18 and 9 times more offspring than adults on FX-10 and NUF-76, respectively. Plant anatomical and biochemical studies are required to investigate the exact cause of antixenosis in FX-10 and NUF-76 and possible antibiosis in NUF-76.