Cross-resistance and synergism bioassays suggest multiple mechanisms of pyrethroid resistance in western corn rootworm populations

Abstract

Recently, resistance to the pyrethroid bifenthrin was detected and confirmed in field populations of western corn rootworm, Diabrotica virgifera virgifera LeConte from southwestern areas of Nebraska and Kansas. As a first step to understand potential mechanisms of resistance, the objectives of this study were i) to assess adult mortality at diagnostic concentration-LC99 to the pyrethroids bifenthrin and tefluthrin as well as DDT, ii) estimate adult and larval susceptibility to the same compounds as well as the organophosphate methyl-parathion, and iii) perform synergism experiments with piperonyl butoxide (PBO) (P450 inhibitor) and S,S,S-tributyl-phosphorotrithioate (DEF) (esterase inhibitor) in field populations. Most of the adult field populations exhibiting some level of bifenthrin resistance exhibited significantly lower mortality to both pyrethroids and DDT than susceptible control populations at the estimated LC99 of susceptible populations. Results of adult dose-mortality bioassays also revealed elevated LC50 values for bifenthrin resistant populations compared to the susceptible control population with resistance ratios ranging from 2.5 to 5.5-fold for bifenthrin, 28 to 54.8-fold for tefluthrin, and 16.3 to 33.0 for DDT. These bioassay results collectively suggest some level of cross-resistance between the pyrethroids and DDT. In addition, both PBO and DEF reduced the resistance ratios for resistant populations although there was a higher reduction in susceptibility of adults exposed to PBO versus DEF. Susceptibility in larvae varied among insecticides and did not correlate with adult susceptibility to tefluthrin and DDT, as most resistance ratios were < 5-fold when compared to the susceptible population. These results suggest that both detoxifying enzymes and target site insensitivity might be involved as resistance mechanisms.

Field efficacy of soil insecticides on pyrethroid‐resistant western corn rootworms (Diabrotica virgifera virgifera LeConte)

“…In 2016 and 2017, replicated field trials were conducted in continuous maize to evaluate the performance of soil insecticides at three geographic locations in Nebraska, US, where different levels of WCR susceptibility to pyrethroids had been reported . A Saunders county field site was selected to test a pyrethroid‐susceptible WCR population, whereas Clay and Keith county field sites were selected to test populations that exhibited moderate and high levels of WCR pyrethroid resistance, respectively.…”

“…The selection pressure imposed on maize pests from one or more aerial applications of bifenthrin per crop season led to field‐evolved resistance of WCR to bifenthrin in some populations by 2015 . Laboratory bioassays then revealed WCR cross‐resistance to tefluthrin, a common soil insecticide active ingredient, and that resistance levels for both pyrethroids were higher for WCR adults than for larvae . The observed level of resistance was great enough to cause significant reductions in efficacy of formulated bifenthrin when resistant adult WCR were bioassayed at label rates under simulated aerial application conditions .…”

“…The impact of larval pyrethroid resistance levels on the field performance of formulated pyrethroid soil insecticides has not been evaluated. In order to complement a larger project to characterize WCR pyrethroid resistance and to inform WCR management strategies, the present study was designed to (i) evaluate the efficacy of some commonly used formulated soil insecticides against WCR in fields with different levels of WCR pyrethroid resistance and (ii) estimate in the laboratory current susceptibility levels of WCR larvae to the soil insecticide active ingredients.…”

Predation Capacity of Soil-Dwelling Predatory Mites on Two Ground Beetle Immature Stages: A Biological Control Perspective for Two Major Maize Pests

“…In all cases, at least one WCR population evolved and became resistant to the pest control methods. Pesticides (Pereira et al 2017), GMOs (Gassmann et al 2011) and soybean/corn crop rotation became obsolete pest management methods in the areas concerned. Barsics et al (2013) detailed the management pest methods available on Agriotes spp..…”

Sublethal Effects of vATPase-A and Snf7 dsRNAs on Biology of Southern Corn Rootworm, Diabrotica undecimpunctata howardi Barber

“…The use of RNAi plants expressing dsRNA pyramided with Bt toxins to control corn rootworm (MON 87411) has recently been registered by the Environmental Protection Agency (EPA 2017) and will be commercially available to corn growers in near future (Ahmad et al 2016, Bachman et al 2016, Head et al 2017. Given the recent evolution of WCR resistance to different corn hybrids expressing Bacillus thuringiensis Berliner traits (Gassmann et al 2014(Gassmann et al , 2016Wangila et al 2015;Andow et al 2016;Zukoff et al 2016b;Ludwick et al 2017) as well as to pyrethroid insecticides (Pereira et al 2015(Pereira et al , 2017, new technologies with unique mode of actions are urgently needed to mitigate existing resistance and to develop sustainable WCR management programs.…”