Anticarsia gemmatalis nucleopolyhedrovirus from soybean crops in Tamaulipas, Mexico: diversity and insecticidal characteristics of individual variants and their co-occluded mixtures
Keywords:
baculovirus, genotypic mixtures, pathogenicity, speed-of-kill, virus productionAbstract
In 1999, Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) was introduced into a major soybean-growing region in Tamaulipas, Mexico, for control of its lepidopteran host, Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae). The virus introduction proved to be highly successful in controlling this agronomically important pest. In order to determine the genotypic diversity and insecticidal traits of Mexican AgMNPVs, we obtained 30 field-collected isolates from Tamaulipas State. Five distinct variants (genotypes 1–5) were identified from plaques replicated in A. gemmatalis larvae by examination of restriction profiles using HindIII. Initial screening indicated that none of the variants, or co-occluded mixtures of variants in different proportions, was more pathogenic than the 30 field isolates mixture or a reference variant from Brazil (AgMNPV-2D). Mean occlusion body production also was similar among genotype variants, the mixture of 30 field isolates and AgMNPV-2D treatments, but was significantly reduced in 1 co-occluded mixture. Speed of kill also was similar among variants (except genotype 1) and their mixtures. Lethal concentration metrics indicated that these results were unlikely due to selection of variants with reduced pathogenicity during the plaque purification process. We conclude that the mixture of 30 field isolates most likely would prove suitable for use as a biological insecticide in the soybean-growing region of Mexico.
Resumen
En 1999, el nucleopoliedrovirus de Anticarsia gemmatalis (AgMNPV) fue introducido a una importante región de producción de soya en Tamaulipas, México para controlar el lepidóptero huésped, Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae). La introducción del virus demostró ser muy exitosa en el control de esta importante plaga agrícola. Para determinar la diversidad genotípica y las características insecticidas de los AgMNPVs de México, obtuvimos 30 aislados colectados en campos de soya del estado de Tamaulipas. Mediante el uso de la enzima de restricción HindIII, se identificaron cinco variantes distintas (genotipos 1–5) que replicaron en A. gemmatalis. Los ensayos indicaron que ninguna de las variantes, ni mezclas coocluidas de las mismas en diferentes proporciones, tuvieron una patogenicidad mayor que la de la mezcla de 30 aislados silvestres, o de una variante de referencia de Brasil (AgMNPV-2D). La producción de cuerpos de oclusión fue similar entre las variantes, la mezcla de 30 aislados silvestres y el AgMNPV-2D, aunque la producción fue significativamente reducida en una mezcla de variantes coocluidas. El tiempo medio de matar también fue similar entre las variantes (excepto el genotipo 1) y las mezclas de variantes. Ensayos de concentración-mortalidad indicaron que durante el proceso de purificación de placa no hubo selección de variantes con menores características de patogenicidad. Concluimos que la mezcla de 30 aislados silvestres podría ser el ingrediente activo de un insecticida biológico en esta región de producción de soya en México.
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