Relationships between Cry1Ac and Cry2Ab protein expression in field-grown Bollgard II® cotton and efficacy against Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae)

Effects of seasonal changes in cotton plants on the evolution of resistance to pyramided cotton producing the Bt toxins Cry1Ac and Cry1F in Helicoverpa zea

“…5,6 Bt toxin concentration varies substantially within and among Bt cultivars, and seasonal declines in toxin concentration are common for Bt corn, cotton, and soybean. 5,[15][16][17][18][19][20][21][22] Such declines may be associated with increased survival of susceptible insects on Bt crops and increased dominance of resistance in pests with low susceptibility to Bt toxins. [22][23][24][25][26] Accordingly, it was hypothesized that seasonal declines in the concentration of Bt toxins could accelerate evolution of resistance to pyramids in pests with low inherent susceptibility to Bt toxins.…”

“…5,[15][16][17][18][19][20][21][22] Such declines may be associated with increased survival of susceptible insects on Bt crops and increased dominance of resistance in pests with low susceptibility to Bt toxins. [22][23][24][25][26] Accordingly, it was hypothesized that seasonal declines in the concentration of Bt toxins could accelerate evolution of resistance to pyramids in pests with low inherent susceptibility to Bt toxins. 5,14,27 Nevertheless, resistance evolution is determined by relative fitness of genotypes with and without resistance alleles on Bt crops and non-Bt host plants in 628 www.soci.org Y Carrière et al…”

Survival of Helicoverpa armigera larvae on and Bt toxin expression in various parts of transgenic Bt cotton (Bollgard II) plants

“…All of the Cry measurements reported in the literature were determined from samples collected from field‐grown cotton plants (Adamczyk et al., ,b; Gore et al., ; Stewart et al., ; Greenplate et al., ; Kranthi et al., ; Sivasupramaniam et al., ; Lu et al., ; Knight et al., ; Luong et al., ). It is possible that there is a change in Cry protein expression in Bollgard II cotton grown under greenhouse conditions.…”

“…Parker & Luttrell (1999) reported that larvae of Heliothis virescens (Fabricius) moved from Bollgard II plant terminals more rapidly than from non-Bollgard II plant terminals, but the fate of the larvae after they left the terminals was not reported. Many studies reported variations in Cry protein expression among plant parts (Greenplate et al, 2003;Kranthi et al, 2005;Sivasupramaniam et al, 2008;Lu et al, 2011;Knight et al, 2016). For example, Anilkumar et al (2009) reported that Cry1Ac toxin contents were 8-179 higher in leaves than in flowers of Bt cotton.…”

Bt resistance in Australian insect pest species

“…Unfortunately, protein levels of Cry1Ac are often suboptimal in existing Bt cotton crops, especially later in the season [29][30][31]. Llewellyn et al [32] reported that efficacy of Vip3A also declined as the season progressed, although not as markedly as Cry1Ac.…”