Consolidated technology: Trichogramma in lepidopteran management

Biological control has arrived in Brazil to stay, although it still needs to overcome challenges. This is the case of Trichogramma, a tiny natural enemy that measures 0,25 mm and parasitizes mainly Lepidoptera eggs.

09.07.2018 | 20:59 (UTC -3)

Several families of insects have representatives of egg parasitoids, which are important because by destroying the initial phase of the insect life cycle, they prevent damage to agricultural crops.

Among the various representatives, Trichogramma It is one of the most studied and used in the world, since the beginning of the last century, being used on 20 million hectares in different parts of the world.

The literature on the aforementioned parasitoid is vast, with numerous publications, including in Brazil, with two books on the subject, one in 1997 (PARRA & ZUCCHI, 1997) and another in 2010 (CÔNSOLI, PARRA, ZUCCHI, 2010), and one third dedicated to its taxonomy, in 2011 (QUERINO & ZUCCHI, 2011).

There are more than 200 described species of Trichogramma, 26 of them referred to in Brazil.

Studies with Trichogramma, a tiny natural enemy (0,25 mm) that parasitizes mainly Lepidoptera eggs, started in Brazil to control Neoleucinodes elegantalis in tomato plants, in Rio de Janeiro (GOMES, 1963). They were then studied to control forest pests by a group from Minas Gerais, led by George Washington Moraes from UFMG (MORAES, BRUN AND SOARES, 1983).

Later, in 1984, in the Department of Entomology and Acarology at ESALQ/USP, under the influence of a French group, led by Jean Voegelé from INRA, the Biological Control program for agricultural pests began with Trichogramma, initially with the aim of controlling the sugarcane borer Diatraea saccharalis and cotton pests, Heliothis virescens, the apple caterpillar and Alabama argillacea, the cotton leafworm. It was a program containing different stages, multidisciplinary and that today, after 30 years, is beginning to be widely used in Brazil, with inundative releases of the parasitoid. It is important to remember that in the current philosophy of Integrated Pest Management (IPM), Trichogramma it may be used alongside other control measures, including chemical control, with the restriction that, in this case, only selective products must be used to avoid the elimination of natural enemies that have been released into the field.

One of the great advantages of this parasitoid lies in the fact that by destroying the embryo, it prevents the plague from progressing. Furthermore, to be multiplied in the laboratory for release in the field, it can be created in alternative hosts, in this case, moths, easily created in the laboratory.

This was discovered by Flanders in the late 1920s in the USA, and moths continue to be used to this day. Flanders indicated the corn moth as an alternative host, Sitotroga cerealella, which is still used today in some countries. In the 1970s, it was discovered that the moth Anagasta kuehniella it was a better host than the corn moth and should replace it. Studies show that this moth is actually the most efficient, as it is richer in nutrients, for the Brazilian species sold, that is, Trichogramma galloi, Trichogramma pretiosum e Trichogramma atopovirilia. The Chinese use peanut moth eggs, Corcyra cephalonica, or even ovules or eggs of silkworm species.

There are companies in the world that produce around 40kg of moth eggs per day, as they are used to create the parasitoid Trichogramma and various predators. It is worth noting that 1g of moth eggs A. kueniella contains 36.000 eggs.

There are many basic studies of the natural enemy Trichogramma, which allows its production in the laboratory (PARRA et al., 2014).

It is a very specialized insect that is attracted by volatile substances found in the scales of lepidopteran pests when they lay eggs. These volatiles that favor the Trichogramma and which are called kairomones, have even been identified as tricosane.

The life cycle of Trichogramma pretiosum e T. galloi and other species are variable according to temperature (Table 1).

Tabela 1 Life cycle of T. pretiosum e T. galloi at different temperatures

Temperature

° C

T. pretiosum

T. galloi

18

27,3

31,3

20

19,4

19,5

22

15,4

15,6

25

9,7

12,1

28

7,1

-

30

8,6

8,0

32

6,7

7,1

Temperature

° C

T. pretiosum

T. galloi

18

27,3

31,3

20

19,4

19,5

22

15,4

15,6

25

9,7

12,1

28

7,1

-

30

8,6

8,0

32

6,7

7,1

 

A female of Trichogramma lays 70 to 120 eggs, with 1, 2, 3 wasps or sometimes a large number of parasitoids being able to emerge from each parasitized egg, depending on the size of the host egg.

Currently, there are companies selling Trichogramma, which is released inundatively and which therefore has a faster action, more similar to the agrochemicals with which farmers are more familiar. This is called Applied or Augmentative Biological Control.

After 30 years of studies in Brazil, Trichogramma is already a reality in our country, with 500.000 ha of sugar cane being released to control the sugarcane borer, Diatraea saccharalis, And T. pretiosum, which is released in soybeans to control anticarsia gemmatalis, Chrysodeixis includens e Helicoverpa armigera, with other examples in tomato, to control Absolutely all, in addition to being used in beans, cotton and corn (helicoverpa zea). It is efficient in open fields, organic farming or greenhouse conditions.

How and when to use it?

As mentioned, T. galloi has already been used in large areas of sugar cane and T. pretiosum also in large areas of soybeans, corn, cotton, to control C. includens, A. gemmatalis e H. Armigera, the equivalent of more than 250.000 ha, no longer being used due to the non-availability of biological input.

In other countries, Biological Control is generally more used, but mainly in more restricted areas, that is, greenhouses. Our Agriculture is peculiar, as there are large areas, sometimes 30.000 ha, 50.000 ha, 100.000ha, of a crop exploited by a single farmer.

Evidently, in this case, there are problems in surveying the pest, which must be sampled at the beginning of the culture and after the eggs are detected, the parasitoids must be released.

How to carry out a population survey

By the conventional method, for example, in soybeans, with a visual method, baits or “beating cloth” (to detect caterpillars).

This is difficult in large areas. Therefore, to make biological control viable in larger areas, other methods must be used to begin the release: pheromones, or even new Remote Sensing techniques must be developed.

And the release? It must be manual, with motorcycles, or with something more sophisticated like planes or drones (these are being studied).

And ants, very abundant predators in our country, should be avoided. The release forms must protect natural enemies, with the use of capsules made of biodegradable material, already used, which allow the exit of the Trichogramma, but they prevent ants from entering. Release of Trichogramma adults would be another option. The quantity to be released must vary from 50.000 parasitoids/ha to 200.000 parasitoids/ha; In Brazil, high soil temperatures can make the emergence of the natural enemy unfeasible, as they can reach 60°C in summer.

Therefore, to increase the areas treated with Trichogramma, there are obstacles to be overcome including: “farmer’s insecticide culture”; increase the extension service for transferring technology to the user; monitoring appropriate to the Brazilian reality; supply and quality of the natural enemy; storage and transport logistics; appropriate legislation for natural enemies; use of selective chemicals and release techniques (PARRA, 2014).

For Trichogramma, the collection site of the “lineage or species” is very important, as if this process is carried out in a cold climate, the parasitoid may not be suitable for release in a hot climate and vice versa. The lack of concern about this fact tends to lead to poor control results.

Therefore, biological control is here to stay after the introduction of H. armigera. However, for Brazil to progress and change the “farmer's mind” it is necessary to overcome challenges, especially considering the dynamism of Brazilian agriculture and the large areas with transgenic plants currently used with soy and corn. In general, if used well, biological control is competitive with chemical control, with well-known ecological and social advantages.

The article is in issue 190 of Cultivar Grandes Culturas. 

Mosaic Biosciences March 2024