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.
Highlights
Cotton leafworm Alabama argillacea (Hubner) (Lepidoptera: Noctuidae) is a species native to Southern and Central America, found in almost all cotton-growing regions, extending from southern Canada to northern Argentina [1].In Brazilian cotton-growing regions, this pest can infest the crop at any stage in its phonological development [2]
There were no interaction effects between cultivar (C) and temperature (T) (F(C versus T)4, 196 = 1.53, P = 0.1967) or between the length of time A. argillacea larvae were exposed to the cotton plants (t) and temperature (T) (F(t versus T)12, 196 = 0.99, P = 0.4595) in the percentage of recovered A. argillacea larvae from the cotton plants (Table 1)
According to the analysis of variance, significant differences were found between cultivars Bt and non-Bt (F(C)1, 196 = 151.75, P,0.0001) (Table 1) and among temperatures tested (T) (F(T)4, 196 = 8.53, P,0.0001) (Table 1), but not for the exposure times of A. argillacea larvae to the cotton plants (t) (F(t)3, 196 = 2.12, P = 0.0997) (Table 1) in the percentage of recovered A. argillacea larvae from the cotton plants
Summary
In Brazilian cotton-growing regions, this pest can infest the crop at any stage in its phonological development [2]. In Southern– Central Brazil, it is considered a late pest [3], but in the Northeast, with the exception of Bahia State, it attacks in the initial stages and can occur sporadically when the crop has matured [2]. The cotton leafworm, is highly destructive as one of the main defoliating pests of cotton (Gossypium hirsutum Linnaeus) in Brazil [4]. The most severe attacks occur after the cotton flowering period and are characterized by the destruction of the leaves on the plant’s main stem, which reduces plant growth at any further stage of its development by affecting the height and the stem diameter, and production is damaged [5]. Chemicals are the main method for control; insect resistance to these molecules has been detected [6]
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