**1. Introduction**

[306] Zang, Y., Zhong, Y., Luo, Y., & Kong, Z. M. (2000). Genotoxicity of two novel pesti‐

[307] Zhang, A., Kaiser, H., Maienfisch, P., & Casida, J. E. (2000). Insect nicotinic acetylcho‐ line receptor: conserved neonicotinoid specificity of [3H]imidacloprid binding site. *J.*

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cides for the earthworm, *Eisenia fetida*. *Environ. Pollut.*, 108(2), 271-278.

of cartap on zebrafish embryos. *Aquat. Toxicol.*, 95(4), 339-346.

*Neurochem.*, 75(3), 1294-1303.

414 Insecticides - Development of Safer and More Effective Technologies

The discovery of thiamethoxam has opened new perspectives for the Brazilian agriculture, mainly in seed treatment. The molecule was the center of studies by a group of researchers from official agencies and universities, in order to evaluate its mechanism of action.

Researches were made to establish the activity of the active ingredient on the physiology of the plant, when applied the soybean seed treatment. It was observed that seed germination index and seedling vigor were higher than those of plants in plots without seed treatment. It was also found that, under water stress conditions soybean plants from seed treated with thiamethoxam showed better growth, such as increased length and root volume, faster ini‐ tial development, higher leaf area, height, number of pods and green colored more intense.

The various pesticides used today can be classified into different classes (CASTRO, 2006), such as:


Belonging to both the previous classes, there are: auxins, gibberellins, cytokinins, absci‐ sic acid and ethylene. It is considered, for the bio-regulator acts, that it must primarily bind to a receptor on the plasmatic membrane of the cell.

allowing a greater ionic transport, increasing the mineral nutrition of the plant. This increase in the availability of mineral salts promote positive responses in the development and plant productivity (Figure 1). The second one is related to the higher enzymatic activity caused by thiamethoxam, as the seed level or as the plant one. The highest enzymatic activity would increase both the primary and the secondary metabolism. It would increase the synthesis of amino acids, precursors of new proteins. The plant response to these proteins and hormone

Thiamethoxam: An Inseticide that Improve Seed Rice Germination at Low Temperature

The bioactivators are organic substances, potentially modifying the morphology and physi‐ ology of plants, by acting on the synthesis and action of endogenous hormones and may

In general, insecticides and fungicides are used to control insects and fungi, respectively. However, it has been found that certain chemicals may also exert actions modifying the

**THIAMETHOXAM**

Transcription factors

Gene expression

**PLANT RESPONSES**

Metabolic enzymes

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Plant hormones

Primary and secondary metabolism

Amino acids and precursors of plant hormones

biosynthesis could be related to important increases in production (Figure 2).

lead to increases in productivity.

Protein of membranes

Ionic transport

Mineral nutrition

**Figure 2.** Action mode of thiamethoxam in plants (CASTRO, 2006)

morphology and metabolism of plants.


**Figure 1.** Sequence of events promoted by thiamethoxam (CASTRO, 2006)

Castro (2008), found that the molecule of thiamethoxam is capable of inducing physiological changes in plants. In function of the results obtained, it is concluded that the bioactivator can act in two ways: the first one, is to enable transport proteins from the cell membranes allowing a greater ionic transport, increasing the mineral nutrition of the plant. This increase in the availability of mineral salts promote positive responses in the development and plant productivity (Figure 1). The second one is related to the higher enzymatic activity caused by thiamethoxam, as the seed level or as the plant one. The highest enzymatic activity would increase both the primary and the secondary metabolism. It would increase the synthesis of amino acids, precursors of new proteins. The plant response to these proteins and hormone biosynthesis could be related to important increases in production (Figure 2).

Belonging to both the previous classes, there are: auxins, gibberellins, cytokinins, absci‐ sic acid and ethylene. It is considered, for the bio-regulator acts, that it must primarily

**c.** Plants Stimulants or bio-stimulants - mixtures of plant regulators, occasionally along to‐ gether nutrients, vitamins, amino acids or miscellaneous debris. They exhibit a different stimulatory effect than if application isolated, creating a synergistic effect between regu‐ lators. Some examples of bio-stimulants the Stimulate are Promalin and e mixture GA3 +

**d.** Bioactivators - complex organic substances, that modify the morphology and physiolo‐ gy of plants and are capable of acting in the synthesis and action of endogenous hor‐ mones, leading to increase in productivity. In this class some insecticides fit, such as

bind to a receptor on the plasmatic membrane of the cell.

416 Insecticides - Development of Safer and More Effective Technologies

aldicarb and thiamethoxam, besides of the hydrogen cyanamide.

**Figure 1.** Sequence of events promoted by thiamethoxam (CASTRO, 2006)

Castro (2008), found that the molecule of thiamethoxam is capable of inducing physiological changes in plants. In function of the results obtained, it is concluded that the bioactivator can act in two ways: the first one, is to enable transport proteins from the cell membranes

2,4-D.

The bioactivators are organic substances, potentially modifying the morphology and physi‐ ology of plants, by acting on the synthesis and action of endogenous hormones and may lead to increases in productivity.

In general, insecticides and fungicides are used to control insects and fungi, respectively. However, it has been found that certain chemicals may also exert actions modifying the morphology and metabolism of plants.

**Figure 2.** Action mode of thiamethoxam in plants (CASTRO, 2006)

Certain insecticides like aldicarb, carbofuran and thiamethoxam, may cause a physiological effect promoting changes in certain processes in plant physiology, such as growth, morphol‐ ogy or plant biochemistry.

of product/100kg of seed; Treatment 3 - 200 ml of product/100kg of seed; Treatment 4 - 300 ml of product/100kg of seed and Treatment 5 - 400 ml of product/100kg of seed, pri‐

Thiamethoxam: An Inseticide that Improve Seed Rice Germination at Low Temperature

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The germination test was performed in three replications, eight sub-samples of 50 seeds (400 seeds per replicate) for each cultivar. The seeds were placed to germinate in paper rolls moistened with water equivalent to 2,5 times the weight of the substrate, following the crite‐ ria established by the Rules for Seed Testing (Brazil, 2009). Five germination temperatures were used: 25, 20, 18, 15 and 13°C. The germination test at temperatures of 25 and 20ºC were performed in the germinator, and at temperatures 18, 15 and 13°C held in BOD. The count‐ ing of normal seedlings was performed seven days after sowing for temperatures of 25, 20

According to the results, the rice seeds cultivars BR IRGA 417, BR IRGA 424 and Avax R. treated with thiamethoxam, were superior in all tested temperatures, when compared to the values obtained in the zero dose (without application of thiamethoxam), varying only the

By observing the data shown in Figure 3, it is found that the treated seeds showed signifi‐

The temperatures of 15ºC and 13°C were the most adverse ones, but when the seeds are treated independent from the dose, they showed germination over the zero dose. At the dose of 200 mL/100 kg of seeds at a temperature of 15°C, there was an increase of 21 percent‐ age points, whereas at 13°C this increase was 37 percentage points. At temperatures of 25, 20 and 18ºC this increase was on average 7 percentage points when compared with the zero

Figure 4 shows that seeds treated with thiamethoxam at different temperatures had posi‐ tive additions in relation to the zero dose. The results of this study confirm those ob‐ tained by Castro et al. (2007), working with soybeans, and those by Clavijo (2008) working with rice, when claiming that seeds treated with thiamethoxam had their germi‐ nation accelerated by stimulating the enzymes activity, besides of showing more uniform emergency and stand more uniform and better initial impulse. Also in soybean seeds, Cataneo (2008) observed that thiamethoxam accelerates germination, and induces further development of the embryonic axis. According to the results, rice seeds, cultivars BR IR‐ GA 417, BR IRGA 424 and Avax R. treated with thiamethoxam, were superior in all the tested temperatures, when compared to the values obtained at the zero dose (without ap‐ plication of thiamethoxam), varying only the intensity of this difference due to the dose

and 18°C and at 21 days for temperatures of 15 and 13ºC.

cant increases in germination at different temperatures.

intensity of this difference due to the dose used and the temperature.

**4. Results and discussion**

or to sowing.

dose.

used and temperature.

The thiamethoxam can be applied in seed treatment, by spraying on leaves of plants or by soil application, being absorbed by the roots. Applied as a seed treatment, the thiamethox‐ am can promote the expression of the effect by stimulating root growth and increasing ger‐ mination rate, consequently, reducing the time for field crop establishment.
