Feeding of fall armyworm, Spodoptera frugiperda, on Bt transgenic cotton and its isoline

Abstract

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0 days) than those fed on non‐Bt cotton (20.2 days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042 g) was lower than that of larvae fed on non‐Bt cotton (0.061 g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53 g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61 g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25 g dry weight) than those fed on non‐Bt‐cotton leaves (0.37 g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058 g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056 g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.

Survival and nutritional indexes of Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) maintained in Bt maize for five generations

“…We verified in this study that the conversion of ingested, digested (ECI, ECD) and relative growth (RGR) showed a strong negative correlation with the metabolic cost (CM). Usually, organisms exposed to Bt maize shows high metabolic cost in direct response to the toxins action (Ramalho et al, 2011;Cataño et al, 2014). The estimated nutritional indexes were affected by the evaluated toxins action, as well as the obtained results with the exposure of S. frugiperda to Bt cotton (Ramalho et al, 2011;Cataño et al, 2014).…”

“…The efficiency in the conversion of digested and ingested food are the main nutritional indexes related to the metabolic cost of S. frugiperda to Bt maize (Yinghua et al, 2017). In Bt cotton that synthesizes the Cry1Ac toxin, the efficiency in the conversion of the digested and ingested food for S. frugiperda was reduced by 9.05 and 8.24%, respectively in relation to the control group (Ramalho et al, 2011).…”

“…The changes in metabolized feed (M), relative growth rate (RGR), relative metabolic rate (RMI) and relative consumption rate (RCR) are the result of a deficiency in assimilation and subsequent conversion of nutrients into body material and the inactivation of Bt toxins (Ramalho et al, 2011;Yinghua et al, 2017). In virtue of the presence of toxic substances without interference in palatability, caterpillar intoxication occurs due to the action of Cry toxins, affecting the usage of ingested food (Scriber & Slansky, 1981;Jiang et al, 2013).…”

“…The lower values of Approximate Digestibility (AD) obtained in S. frugiperda not exposed to Bts toxins may be related to fast food digestibility in the intestine of the insect (Ramalho et al, 2011). The rapid transition of food through the digestive tract of the insect reduces the interaction of proteolytic enzymes in the food substrate, causing a decrease in the active toxins in the intestinal lumen (Dinglasan et al, 2009).…”

“…Reports suggest high evolution risk of the S. frugiperda resistance to pyramidal maize and to the Vip3Aa20 event (Bernardi et al, 2015a;Bernardi et al, 2017). The Bt toxins present in plant leaves can affect the amount of food ingested and converted into body matter, as well as increasing energy expense during metabolism (Ramalho et al, 2011). Thus, the aim of this study was to evaluate the survival and nutritional indexes of Spodoptera frugiperda fed with the maize hybrids that synthesize the toxins Cry1F, Cry1A105-Cry2Ab2 and Vip3Aa20 for five generations.…”