Blair D. Siegfried
Lance J. Meinke
Date of this Version
Pereira, A.E. 2016. Assessing the risk of resistance evolution, adult and larval susceptibility, and sublethal effects after exposure of corn rootworms to vacuolar ATPase-A and Snf7 dsRNAs. PhD Dissertation. University of Nebraska.
Corn rootworms are Diabroticite beetles from the genus Diabrotica and include the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, and the northern corn rootworm, D. barberi Smith & Lawrence, as the most important pests in the U.S. Corn Belt. The southern corn rootworm (SCR), D. undecimpunctata howardi Barber, is considered a polyphagous plant pest and feeds in a wide variety of plants including peanuts, cucurbits, soybeans, and especially corn. Resistance to control methods including behavioral resistance to crop rotation and to corn hybrids expressing Bacillus thuringiensis Berliner toxins in WCR has frequently been reported. SCR has been considered a surrogate insect for research, given that it is easier to rear and has a shorter life cycle relative to WCR. RNA interference, a novel mode of action for insect control, will be available for corn rootworm control in near future in corn plants expressing hairpin dsRNA. RNAi has proven effective against both larvae and adults of corn rootworm targeting two lethal housekeeping genes, Snf7 and vacuolar (v)ATPase-A. The initial overall objective of this project was to select a SCR field-generated laboratory colony for resistance to vATPase-A dsRNA and evaluate the genetics and heritability of resistance. After exposing adults and larvae of SCR to vATPase-A dsRNA overlaid on artificial diet for nine generations, no resistance evolution was reported. However, a delay in adult emergence and differences in growth parameters including growth rate, generation time, and doubling time, between the RNAi-selected and control colonies were observed during the exposure of SCR neonates for resistance to concentrations that varied from LC50 to LC75, between generations 9 and 12.
Comparative susceptibility of adults and larvae to two lethal dsRNAs, Snf7 and vATPase-A in SCR and WCR were performed with laboratory populations. Sublethal effects of exposure to LC50 of vATPase-A and Snf7 dsRNA were evaluated, and significant differences in female fecundity, percentage of larval and adult recovery, and cumulative number of eggs per female were observed. These results suggest that sublethal effects of dsRNA could significantly affect overall population dynamics.
The results of this research are a first-step in understanding of the effects of dsRNAs in corn rootworms and may reveal what can potentially occur in the field when corn hybrids expressing dsRNAs are deployed in the market.
Advisors: Blair D. Siegfried, Lance J. Meinke