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Optical brighteners for bioinsecticides

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06.09.2004

Optical brighteners are a valuable component for bioinsecticide formulae based on baculovirus. These substances enhance their insecticidal capacity at the same time as they do not favour the development of resistance of the insects to these viruses, nor do they increase the probability that the insect might develop sublethal infections, rather than lethal ones. This is the conclusion of the Mexican engineer, Ana Mabel Martínez Castillo, in her thesis defended in the Public University of Navarre.

Plagues that effect maize

Baculovirus are a group of virus pathogens, specific to arthropods, that are currently used as bioinsecticides in various countries in the world. Their use on the land has shown that ultraviolet radiation from the sun is the main factor that affects the infectious capacity of the viral particles, provoking a drop in the efficacy of these bioinsecticides. For this reason, studies have been initiated in order to identify substances that, incorporated into the baculovirus formulae, enable an increase in its effectiveness and persistence.

This PhD is precisely within this context, evaluating the effect of several optical brighteners, belonging to four different chemical groups, on the insecticidal activity of a specific type of baculovirus - the nucleopolyhedrovirus SfMNPV – which forms the most important maize plague in Latin America, i.e. in the larvae of the Spodoptera frugiperda (J. E. Smith).

Ana Mabel Martínez Castillo concluded that, of the ten optical brighteners studied, the Blancophor BBH and the Calcofluour M2R, both stilbene-derived optical brighteners, were the most effective. Furthermore, the incorporation of Tinopal UNPA-GX into the diet of S. frugiperda significantly reduced the weight of larvae and pupa up to 28% and 13% respectively. Also, the duration of larval development increased up to 30% in the presence of the optical brightener.

Resistance to viruses

The author also concluded that the use of optical brighteners in the formulae of bioinsecticides does not increase the probability of developing resistance to these products in Spodoptera frugiperda plagues.

On the other hand, she points out that significant reductions in the pupal weight as well as in the fecundity and longevity of S. frugiperda adults exposed to Tinopal LPW, alone or mixed with SfMNPV, can be observed.

Regarding the possible influence of the optical brighteners on the lethality of baculovirus-based bioinsecticides, Ana Mabel Martínez Castillo points out that, far from what was expected, the results show that inoculation of the larvae of S. frugiperda mixed with SfMNPV and the optical brightener, Tinopal UNPA-GX, does not produce an increase in sub-lethal infections.

Garazi Andonegi | Source: alphagalileo
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