Impact of the resistance to Pirimicarb on the ability of the cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae) in transmitting plant viruses

Abstract

The present investigations were undertaken to identify the relationship between pirimicarb resistance in Aphis gossypii Glover and its transmitting cucumber mosaic virus (CMV) potency to squash plants.

Data show that the percent of plants infested by mosaic virus transmitted by the dark form of cotton aphid, commonly, was higher than that inoculated by the light form. In the base line of Assiut aphid colony, virus infestation% caused by light and dark forms were 46.3 and 55.5 respectively, whereas, the infestation percentages of light and dark colored forms after one year of pirimicarb selection were 65.1 and 94.3 respectively. Data of light and dark colored forms of New Valley aphid colony, gave the same trend of Assiut aphids. The percent of plants infested by mosaic virus transmitted by the dark form of cotton aphid was higher than that inoculated by the light form. In the base line of Assiut aphid colony, virus inoculation periods in case of light and dark forms were 23.0 and 11.0 days respectively and after one year of Pirimicarb selection were 15.0 and 7.5 days respectively. The inoculation period of mosaic virus transmitted by the dark form of cotton aphid, commonly, was shorter than that of the light form. In the present study, it is clear that the ability of cotton aphid expressed as % infection of inoculated plants is resistant correlation as 64% of the differences in plant virus infestation are due to the level of pirimicarb resistant value. This finding may be attributed to the inoculation period which has a negative correlation with the pirimicarb resistance level. This negative correlation means that the more of resistance level, the less of inoculated period. The coefficient of determination was found to be 0.7 which indicates that 70% of the variability in inoculation period is due to pirimicarb resistance level. Our studies lead to the fact that the presence of the dark form of cotton aphid in the normal conditions is an alarm telling us that the aphid colony is going toward insecticide resistance subsequently, spread of plant virus diseases. Therefore, farmers must pay attention to the integrated pest management programs, without the use of chemical control methods to avoid the appearance of resistant strains (dark forms).