Feeding and Dispersal Behavior of the Cotton Leafworm, Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), on Bt and Non-Bt Cotton: Implications for Evolution and Resistance Management

Abstract

The host acceptance of neonate Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) larvae to Bt cotton plants exerts a strong influence on the potential risk that this pest will develop resistance to Bt cotton. This will also determine the efficiency of management strategies to prevent its resistance such as the “refuge-in-the-bag” strategy. In this study, we assessed the acceptance of neonate A. argillacea larvae to Bt and non-Bt cotton plants at different temperatures during the first 24 h after hatching. Two cotton cultivars were used in the study, one a Bt DP 404 BG (Bollgard) cultivar, and the other, an untransformed isoline, DP 4049 cultivar. There was a greater acceptance by live neonate A. argillacea larvae for the non-Bt cotton plants compared with the Bt cotton plants, especially in the time interval between 18 and 24 h. The percentages of neonate A. argillacea larvae found on Bt or non-Bt plants were lower when exposed to temperatures of 31 and 34°C. The low acceptance of A. argillacea larvae for Bt cotton plants at high temperatures stimulated the dispersion of A. argillacea larvae. Our results support the hypothesis that the dispersion and/or feeding behavior of neonate A. argillacea larvae is different between Bt and non-Bt cotton. The presence of the Cry1Ac toxin in Bt cotton plants, and its probable detection by the A. argillacea larvae tasting or eating it, increases the probability of dispersion from the plant where the larvae began. These findings may help to understand how the A. argillacea larvae detect the Cry1Ac toxin in Bt cotton and how the toxin affects the dispersion behavior of the larvae over time. Therefore, our results are extremely important for the management of resistance in populations of A. argillacea on Bt cotton.

Effects of temperature on the feeding behavior of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) on Bt and non-Bt cotton plants

“…Whenever they are in high density populations, Lepidoptera cause great loss in crop yield. Cotton leafworm Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) stands out among such species, due to its destructive capacity (Ramalho et al 2014). Destruction may occur from the initial phase to the crop maturation in all cotton producer regions in Brazil (Ramalho et al 2014).…”

“…Thus, cotton pest control is a limiting factor to the cultivation of this malvaceae, since they represent high production cost due to the countless spraying needed to control insect pests (Ramalho et al 2014). FRANCISCO S. RAMALHO et al The use of cotton cultivars resistant to cotton leafworm has been suggested as an alternative to chemical control (Schnepf et al 1999).…”

“…However, Lepidoptera monofage as that shown by A. argillacea and the continuous expression of Cry toxins in Bt plants put high selection pressure over target insect populations and, consequently, change the host selection behavior by the larva. Therefore, it favors resistance evolution, since dispersion and/ or the feeding behavior of A. argillacea is different between Bt and non-Bt cotton plants (Ramalho et al 2014). Spodoptera frugiperda (J.E.…”

“…The companies follow the aforementioned procedure so the bags can be sold to producers. However, some implications of this seed mixing technique must be observed, since A. argillacea larvae that emerge on Bt plants may do some tasting and get dispersed (Ramalho et al 2014). Larvae that emerge on nonBt plants may also do tasting, stop feeding and move to a transgenic plant (Gould 2000).…”

“…Lepidoptera neonate pre and post feeding scattering is common when the host has toxins such as those derived from B. thurigiensis (Zalucki et al 2002). The movement of A. argillacea larvae from a Bt to a non-Bt cotton plant may lead them to ingest sufficient toxin to make this strategy effective against the pest, and therefore, it helps to stop these toxins to emerge in A. argillacea populations (Ramalho et al 2014). With regard to refuge in the bag "RIB" strategy, the biggest "concern" lies on the fact that the larval movement between Bt and non-Bt plants may booster the resistance evolution in target pest populations (Wangila et al 2012).…”