Efficiency of active ingredients in the control of Spodoptera albula in soybeans

Able to go unnoticed in the field, due to lack of identification, Spodoptera albula has just been detected in soybean crops in Goiás and Mato Grosso. Favored by the Brazilian cultivation system, in which soybeans are the main crop followed by corn, this pest has the potential to become part of the main group of the caterpillar complex of the genus Spodoptera. Studies on the level of control and efficiency of active ingredients need to be further explored to further address this challenge.

Spodoptera albula It is a pest that has a wide geographic distribution, as it can be found in different locations such as the USA, the Caribbean, Central America and South America. In Brazil, its first record was last decade in the southeast region, attacking the peanut crop. It is a species of caterpillar that feeds on leaves and fruits, and can cause economic damage to various crops such as soybeans, corn, sorghum, sunflower, cotton and vegetables, resulting in losses for rural producers.

It has a high reproductive potential, as a female has the capacity to oviposit, one to four overlapping layers with 100 eggs to 250 eggs, which can hatch within six days after laying, depending on weather conditions. The first instar caterpillars scrape the leaf blade and, as they develop, completely destroy the leaf. They are generally found in reboleiras due to the form of mass oviposition, by the adult, in the middle third of the host plant.

The caterpillars' color varies from grayish-black to grayish-brown, with two dorsal rows of dark triangular spots, each with a white dot in the center (figure 1AB). The lateral line is absent or weak and the dorsal and subdorsal lines are often bright yellow, red or orange, and may be weakly marked and the head is brown with black spots (King & Saunders, 1984).

After completing its cycle, the caterpillar leaves the plant, heads to the soil, and transforms into a pupa, reddish to almost black in color, lasting 15 to 17 days.

The moths of this species have a wingspan of 26mm to 37mm, gray forewings and bodies and white hindwings, but they are often translucent (figure 2) and can live for approximately 12 days. Generally, after the third or fourth day of the female's emergence, oviposition occurs. Thus, the complete development cycle of the insect, which begins from the egg to adult stage, is approximately 30 days. 

The adults of this species are nocturnal, are not active during the day, and are found in shelters close to the ground, generally under leaves. If there is any disturbance, they fly randomly until they find a place where they can hide. Two to four hours, after sunset, the active period of adults begins, in which  moths move close to host plants for feeding, mating and oviposition (Todd & Poole, 1980).

In the caterpillar stage, S. albula share with Spodoptera eridania e cosmioides spodoptera many similar morphological and biological characteristics, which makes identification difficult. Therefore, it is possible that this pest is widespread throughout Brazilian regions, going unnoticed in the eyes of field professionals.

In recent years, it has been found in soybean crops, but in low populations, not reaching control levels recommended for other caterpillars of the same genus. The current production system, in which soy is the main crop followed by corn, cotton or sorghum, has probably favored the development and adaptation of this pest, causing population outbreaks. In this way, gradually, S albula It has been gaining ground and appearing more frequently, making its correct identification crucial for control.

In the 2016 summer harvest, caterpillars S. albula were found attacking soybean crops, in the municipalities of Rio Verde and Santo Antônio da Barra, in Goiás and Querência, in Mato Grosso, making it necessary to carry out chemical control of the insect in the latter area. Caterpillars were found active during the day and in "twinkles" with a diameter of approximately 12 meters, forming islands of non-homogeneous infestation in the crop, causing defoliation in the upper thirds of the plants, preserving the central veins of the leaf blade (figure 3AB). An average of 10 individuals were sampled (3^o  urge to 5^o instar) per meter of beating cloth, which were identified by researcher Alexandre Specht (Embrapa Cerrados, Planaltina DF).

S. albula has tolerance to several chemical insecticides as observed in the municipality of Querência at Fazenda São Cristóvão (BR-242), 12°46'10.82” S and 52°13'43.62" W, where there was a need for two applications with different active ingredients (spinosyn and diamide, respectively) at an interval of 7 days.

Like other species of the genus spodoptera, albula has resistance to the Cry1Ac gene Bacillus thuringiensis. Therefore, it is evident that studies, associated with Integrated Pest Management, are an important tool to achieve better management against this pest. For example, monitoring using  traps to capture adults, as a way of ascertaining the presence of the pest, time of infestation, location and population level. This forms the basis for decision-making to control S. albula can be defined by the producer. The association and rotation of insecticides can prevent this pest from causing damage to the crop and prevent active ingredients from losing their effectiveness. The elimination of volunteer plants and crop residues is important to avoid or reduce the potential for attack and reinfestation by this pest for the next harvest or the new crop to be implemented.

Still, there are few studies related to the level of control of S. albula, host weed plants and efficiency of active ingredients, which shows the need to know more about this species, which could become part of the main group of the caterpillar complex of the genus spodoptera.

Antonio Germano C. Rocha and Eduardo Lima de Carmo, University of Rio Verde

Article published in issue 203 of Cultivar Grandes Culturas.