Fig 1.
U.S. map showing states Utah, Nebraska (counties Keith, Perkins, Chase, Saunders, Clay, Cuming, and Washington), and Kansas (counties Sherman and Finney) where western corn rootworm beetles were collected for diagnostic concentration and susceptibility bioassays.
Numbers in the enlarged counties Keith, Perkins, and Chase in Nebraska, and Finney in Kansas, correspond to population numbers listed from these counties in Fig 2 and Tables 2–4 and show spatially where collections were made. Dots within remaining counties and Utah also show spatial locations of collections.
Fig 2.
Mean proportion western corn rootworm adult mortality (± SE) at diagnostic concentration (LC99) of field populations and a susceptible non-diapause population in 2014 and 2015 bioassays for the insecticides bifenthrin, tefluthrin, and DDT.
N = at least 10 reps of 10 beetles per bioassay; LC99: Bifenthrin = 0.77 μg/vial; Tefluthrin = 0.60 μg/vial; DDT = 6.02 μg/vial. Within insecticides, means with the same letter above bars are not significantly different (LSmeans test, p>0.05). Bifenthrin data for 2014 taken from Pereira et al. (2015).
Table 1.
Baseline susceptibility and diagnostic concentration (LC99) (± 95% confidence interval) of western corn rootworm adults by contact to bifenthrin, tefluthrin, and DDT generated from laboratory colonies.
Table 2.
WCR adult susceptibility and RRs to four insecticides between field populations collected in 2015 considered resistant (Keith County populations, NE) and susceptible (Saunders Co-NE), including a susceptible non-diapause population.
Table 3.
WCR adult susceptibility of field populations to tefluthrin with and without synergists PBO (cytochrome P-450 monooxigenases inhibitor) and DEF (esterases inhibitor) and respective RR.
Table 4.
WCR larval susceptibility and RRs of field and non-diapause laboratory populations to the insecticides bifenthrin, tefluthrin, DDT, and methyl parathion.
Diapause eggs were collected from field populations in 2014 and 2015 (Keith populations) and bioassays performed in 2015 and 2016 (Keith populations).