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Quality control is the key to rear efficient natural enemies for FAW

By: Pedro Holtz de Paula, Aloisio Coelho Jr., José Roberto P. Parra

 

The parasitoid wasp Telenomus remus is well known in the field of biological control. It is a potential agent to control Spodoptera frugiperda, with a few important examples of its use in South American countries (Colombia and Venezuela).

In recent decades, several studies have evaluated the biology, parasitism, dispersal, and interaction of T. remus with other parasitoids. However, most results diverge somewhat between laboratory and field experiments. These divergences can occur because rearing for several generations in laboratory conditions can change some population traits, producing parasitoids that are not adapted to the agroecosystem.

One of the most common rearing problems is the degenerative effect of inbreeding. This occurs through the increase in the expression of deleterious or lethal alleles within the population, caused by consanguineous crosses that occur more commonly in laboratory conditions. In the case of haplodiploid wasps such as T. remus, this effect does not occur. However, in haplodiploid species a selection pressure is created and a kind of genetic funnel occurs, which over generations selects insects that are more adapted to the laboratory and less to the external environment. This phenomenon makes it essential to employ quality control during the rearing of a control agent, so that the parasitoids maintain their desirable characteristics and do not lose their efficiency in the field.

Care must be taken after the rearing begins, taking into account the founder effect, to choose a population of sufficient size to maintain high genetic variability and minimize the risk of genetic drift. Also, the environmental rearing conditions must be close to the optimum temperature (around 25 °C) and relative humidity (75% RH). The choice of host and the quality of the eggs are directly associated with the parasitism rate and the quality of the insects in the next generation. Factitious hosts can be used for T. remus mass rearing. However, some investigators have demonstrated a loss of quality over the generations; such a loss during T. remus rearing can occur because of a synergism between the loss of quality due to selection of less-vigorous insects and a nutritionally unsuitable host. A rearing protocol using a host population with known quality ensures more vigorous parasitoids. It is important to standardize each stage of the laboratory rearing protocol, so that fewer variables can affect the population and certain desirable biological characteristics are retained.              

 

References used:

CAVE, R. D. Biology, ecology and use in pest management of Telenomus remus. Biocontrol News and Information, 21(1), 21–26, 2000.

 

FIGUEIREDO, M. L. C.; LUCIA, T. M. C. D.; CRUZ, I. Effect of Telenomus remus Nixon (Hymenoptera: Scelionidae) Density on Control of Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) Egg Masses upon Release in a Maize Field. Revista Brasileira de Milho e Sorgo, 1(2), 12–19, 2015.

 

PREZOTTI, L., PARRA, J. R. P., VENCOVSKY, R., COELHO, A. S., & CRUZ, I. Effect of the size of the founder population on the quality of sexual populations of Trichogramma pretiosum, in laboratory. Biological Control, 30(2), 174–180, 2004.

 

SCHWARTZ, A.; GERLING, D. Adult biology of Telenomus remus [Hymenoptera: Scelionidae] under laboratory conditions. Entomophaga, 19(4), 483–492, 1974.

 

VAN LENTEREN, J. C. et al. Quality control and production of biological control agents: theory and testing procedures. Cabi Publishing, 2003.

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Manju Thakur
Manju Thakur (@manju_ento)
18 days ago

Hi  Pedro Holtz de Paula
Rightly said! Quality control is very important process of Biological control. Do you think sometimes wild species of insects can be mixed with laboratory reared populations to maintain their vigour, at least minimizing the degenerative effect of inbreeding?

Aloisio Coelho Jr.
Aloisio Coelho Jr. (@aloisiocoelho)
Reply to  Manju Thakur
5 days ago

Hi Manju, as Pedro said is costly for companies do this introduction of wild genotypes, in this way we are figuring out some way to keep the quality on the laboratory populations.