Fitness Costs and Incomplete Resistance Associated with Delayed Evolution of Practical Resistance to Bt Crops

Abstract

Insect pests are increasingly evolving practical resistance to insecticidal transgenic crops that produce Bacillus thuringiensis (Bt) proteins. Here, we analyzed data from the literature to evaluate the association between practical resistance to Bt crops and two pest traits: fitness costs and incomplete resistance. Fitness costs are negative effects of resistance alleles on fitness in the absence of Bt toxins. Incomplete resistance entails a lower fitness of resistant individuals on a Bt crop relative to a comparable non-Bt crop. In 66 studies evaluating strains of nine pest species from six countries, costs in resistant strains were lower in cases with practical resistance (14%) than without practical resistance (30%). Costs in F1 progeny from crosses between resistant and susceptible strains did not differ between cases with and without practical resistance. In 24 studies examining seven pest species from four countries, survival on the Bt crop relative to its non-Bt crop counterpart was higher in cases with practical resistance (0.76) than without practical resistance (0.43). Together with previous findings showing that the nonrecessive inheritance of resistance is associated with practical resistance, these results identify a syndrome associated with practical resistance to Bt crops. Further research on this resistance syndrome could help sustain the efficacy of Bt crops.

Exposure to Cry1 Toxins Increases Long Flight Tendency in Susceptible but Not in Cry1F-Resistant Female Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…In contrast to the increased female pupal weight observed in Benzon, sublethal exposure to Cry1Ac in 456LS4D resulted in significantly lower pupal weight in both females (p = 0.0002) and males (p = 0.0002), when compared to larvae fed the control diet. These observations suggest incomplete resistance [56] and mirror reports of reduced pupal weight after sublethal exposure to Cry proteins in the literature, including S. exigua exposure to Cry1Ac [33,[49][50][51]. The discrepancy in effects between Benzon and 456LS4D strains probably relates to different pleiotropic effects exerted by the concentration of Cry1Ac toxin used in this study, which represents a generally lethal and sublethal treatment for Benzon and 456LS4D, respectively.…”

Frequency and diversity of indoxacarb resistance in Australian Helicoverpa armigera (Lepidoptera: Noctuidae)

“…Evaluation of fitness and stability in selected populations has a high level of practical importance for determining resistance risk associated with the use of insecticides and can be useful for formulating insecticide resistance management strategies (Carrière and Tabashnik 2001, 2023). Recent studies of indoxacarb resistant noctuid populations showed significantly slower growth and development, and lower fecundity in S. frugiperda (Hafeez et al 2022b) and H. armigera (Cui et al 2018) suggesting the presence of indoxacarb resistance genes in these populations was deleterious.…”

Genetically Modified Plants Based on Bacillus Genes and Commercial Bacillus-Based Biopesticides for Sustainable Agriculture

“…In this sense, the main concern about the potential risks of recombinant Bt strains and GM-Bt crops is the impact on non-target beneficial species [70], the effects of introducing genes to the relevant microorganisms and unpredicted effects among others, especially food safety (Figure 4). To avoid the problem of their impact on non-target beneficial species, the main aim is to increase host specificity and persistence to achieve better efficacy and lower insect resistance [74][75][76][77]. Laboratory and field studies have been conducted on the effects of GM crops on the environment and human health, resulting in little risk for human health [76][77][78].…”

“…To avoid the problem of their impact on non-target beneficial species, the main aim is to increase host specificity and persistence to achieve better efficacy and lower insect resistance [74][75][76][77]. Laboratory and field studies have been conducted on the effects of GM crops on the environment and human health, resulting in little risk for human health [76][77][78]. Risks are assessed by performing laboratory tests, followed by small-and large-scale field trials to ascertain environmental safety before the release a commercial transgenic crop.…”

“…There have been several studies regarding human health and how Bt food can influence health in humans, demonstrating that Bt toxins are easily degraded in the presence of digestive fluids of the human gut within 0-7 min. Therefore, the risk of Bt foods for human health is small [42,[71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90]. A recent review gives evidence that Bt maize is highly selective against pests with relatively few negative consequences, especially when compared with chemical insecticides [78,80].…”