Pest insects in tropical pastures/ Spodoptera frugiperda

In previous chapters it has been made clear that the biological cycle of the insect is influenced by the temperatures present in the ecosystem where it develops, in the Southern Area of Lake Maracaibo a higher incidence of the insect has been observed in the months where greater rainfall is generated (June, July), although currently the climatic conditions are very variable.

On the other hand, when the eggs hatch, the larvae appear that in their first instars cause scrapes on the tender parts of the leaves, presenting as small translucent areas, because they only leave the lower cuticle of the leaves almost intact, in the same way as the larvae are developing they begin to cause greater damage to the leaves, since it is observed as a kind of cutting or perforations in the leaf blade, sometimes leaving only the central rib of the blade is not checked in time.

Likewise, it is necessary to mention that in some countries it is also known as an army worm, motivated to carry out its attacks in masses, observing high populations of larvae, their attacks on the crop are carried out during the day or at night, once the paddock has been defoliated they move to another in search of plant material. In the case of Corn, apart from defoliating its leaves, the most developed larvae bore the most tender parts of the plant (growth point “sprout”) and penetrate the cobs causing damage to the grains.

As mentioned in previous publications, when planning strategies for the control of a pest, it is necessary to know some aspects concerning the species of insect, plant or organisms that you want to control, among the aspects to be considered are the following:

* Type of plants (host) with which the pest has affinity.

* Tolerance to environmental factors.

* Geographical distribution.

* Responses to certain control alternatives.

In this sense, a diagnosis should be made taking into account the aforementioned criteria with the intention of establishing possible alternatives for the control of the insect, pest or organism. On the other hand, if the field technician visits a farm cultivated with grassland species susceptible to the attack of Spodoptera, it is necessary to inquire with the producer if there have been infestations of fall armyworm of corn in the areas surrounding the farm, in case he does not know the information, he should investigate in the nearby farms to implement preventive measures.

Likewise, it is recommended to keep records about the arrival times of the pest to the crop, the population increase of the pest in relation to the phenological stages of the crop, the rainy periods, among other variables, these data are of interest to make correct decisions when selecting and applying control alternatives.

• An effective preventive control is the biological control with Bacillus thuringiensis (wettable powder) at a rate of 0.5 - 0.75 kg/ha mixed with sufficient water, applying it when the period of greatest incidence of the insect is approaching and when there is the presence of small larvae, the mixture is sprayed evenly over all the foliage, preferably in the morning or in the late afternoon.

• Similarly, an effective control is the use of neem extract combined with Bacillus thuringiensis, because they cause a high mortality of the worm, this alternative was proven by González, Reyes and Hernández (2015), in their research called Biological products for the control of Spodoptera frugiperda(Lepidoptera: Noctuidae), the researchers pointed out that by having native isolates of entomopathogenic fungi and bacteria and plant extracts from the region of origin, adapted to climatic conditions, it guarantees greater toxicity and pathogenicity on the insect.

• As for Corn, one way to prevent the high populations of the worm is to know other host plants that could appear on the cultivated surface, since these also serve as food for the worm and ideal conditions could be generated for a large number of larvae, that is why once the alternative host plants have been identified, they are controlled. According to Ruiz (2000), the three main host families of the Spodoptera frugiperda are the Poaceae in 35.5%, the Fabaceae 11.3%, the Solanaceae and Asteraceae with 4.3%.

It is necessary to take into account this type of alternatives, since crop protection is generated without generating a negative impact on the functional biodiversity of the agroecosystem, since the number of insecticide applications is reduced.

• When establishing a pasture or in already established pastures of stoloniferous growth, it is recommended to carry out an adequate ground preparation using implements such as a plow or light harrows, in order to remove the soil, since in this way the larvae and pupae would be exposed to the birds that feed on them.

• In case of detecting the presence of larvae in the grass crop, overgrazing is recommended to reduce the food source (leaves) and the animals destroy some larvae by the action of trampling, then fertilizers should be applied for the recovery of the pasture, It is necessary to emphasize that this strategy should not be carried out frequently because it could affect the availability of the pasture in the paddock.

When the threshold of infestation by Spodotera larvae is exceeded, it is necessary to resort to the application of insecticides, the most commonly used commercial products are Lorsban 4E in doses of 1L/ha and Lannate in doses of 1.0-1.5 L/ha, with these products good results are obtained but after their application it is convenient to remove the animals from the paddock for an approximate period between 21-30 days, with the intention of prevent the contamination of them. This type of control, as has been mentioned repeatedly, causes an imbalance in agroecosystems, affecting the functional biodiversity present.

Dear farmers, the Spodoptera frugiperda is an insect of high impact in the world agricultural sector, many efforts have been joined for its control, a few months ago in December 2019, the United Nations Food and Agriculture Organization (FAO), launched the Global Action to combat Spodoptera f. contributing 500 million dollars as a response to the rapid spread of fall armyworm, the proposed action seeks to establish working groups for the study of fall armyworm, mobilizing resources for research aimed at the implementation of efficient practices in the control of the larva in crops such as corn, rice, sorghum, vegetables, legumes, among others of importance for food security.

From agrotecnia we reiterate our gratitude to our followers and communities for valuing our agricultural content, this commits us to continue sharing quality information.

Capinera, L. (2001). Manual of Plant pests. San Diego: Academic Press.

Chango, L. (2012). Control of the fall armyworm of corn. Unpublished degree work. Technical University of Ambato, Ecuador.

Fundación Servicio para el Agricultor (2005). Pastures (2nd ed.). Maracaibo: Author.

González, M.; Reyes, N. and Hernández, I. (2015). Biological products for the control of Spodoptera frugiperda (Lepidoptera: Noctuidae). Rev. Colombiana de Entomología, 41(2), 200-204.

Pannuti L.; Baldin, E.; Hunt, T. and Moraes V. (2015). Larval movement in the plant and feeding behavior of the fall armyworm (Lepidoptera: Noctuidae) in the reproductive stages of maize. Revista Entomología, 45, 192-200.