Abstract
The objective was to determine lethal concentrations and to evaluate the effects of sublethal doses of insecticides on Chrysodeixis includens under laboratory conditions. The standard population of C. includens was kept on artificial diet under controlled conditions (25°C ± 5°C, 60% ± 10 RU, 12:12 h). The active principles used were B. thuringiensis, Indoxacarb and Teflubenzuron. The CL25 and LC50 obtained from dose response curve (estimated from eight concentrations of each active principle) were diluted in water and applied to the back of third instar caterpillars and compared to the control (water). The insecticides used showed lethal and sublethal effects in C. includens. Bacillus thuringiensis was 6.21 and 2.79 times more toxic to soybean looper when compared to the products Indoxacarb and Teflubenzuron, respectively. Insecticides applied to the caterpillars reduced survival and affected the biomass gain with increased larvae and pupae longevity, with a significant reduction in fertility (40%) and fecundity (94.97%) in adults. In the present study it was observed that both survival and larval biomass gain have a direct effect on fecundity and fertility, respectively. Therefore the active ingredients Indoxacarb, Teflubenzuron and B. thuringiensis can be used in rotation as a tool in the C. includens.
Highlights
Crops such as soybeans and beans have suffered from constant population outbreaks of Chrysodeixis includens (Walker, 1857) (Lepidoptera: Noctuidae) [1] [2], known as soybean looper [3], with great defoliator potential [4] of polyphagous habit [5].The use of chemicals and transgenic plants is a major control measure employed in the management of C. includens [1] [2]
The active ingredients Indoxacarb, Teflubenzuron and B. thuringiensis can be used in rotation as a tool in the C. includens
Bacillus thuringiensis was considered to be the most toxic product to C. includens because it presented the lowest value for LC50, being 6.21 and 2.79 times lower than the Indoxacarb and Teflubenzuron products, respectively (Table 2)
Summary
The use of chemicals and transgenic plants is a major control measure employed in the management of C. includens [1] [2]. Among the commonly used insecticides, there is an obstacle due to two aspects: resistant, and the lack of knowledge about the lethal and sublethal effects of insecticides on the pest [6] [7]. The toxicity of the insecticide reduces to the ability of a molecule to cause harmful damage to the insect. Since control failures during management [8] may result in exposure of the pest to sublethal doses [7]. Insects that survive after toxic exposure to an insecticide may present changes in biological, reproductive, behavioral and physiological parameters [6] [9]
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