Relationships between selectivity of Aphis gossypii Glover and Aphis craccivora Koch to sucrose and maltose and their resistance to pirimicarb

Abstract

Pirimicarb LC₅₀ base line was determined by the dipping technique in successive concentrations of the trade form of pirimicarb in water. The LC₂₅ was used for the selection every month through a year. In case of 10 sucrose solutions versus water, 8 counts indicated that aphids did not prefer the sucrose solution. After 6 hours the cotton aphid could not discriminate between the sugar solution and water. The discrimination between sugars was enhanced by adding 10% maltose. It was observed that the dark forms of the cotton aphid, A. gossypii and light forms of the cowpea aphid, A. craccivora attracted to the higher sucrose solution than the other forms. The cotton aphid, A. gossypii has a light color as the basic color, transforming under reversible condition to dark green, whereas, the basic color of cowpea aphid, A. craccivora usually black in color, transforming under stress to light brownish. This reversed evidence explained the differences in response towards sugar of the two aphid species.It may be concluded that the dark morphs of A. gossypii, and light morphs of A. craccivora which are considered pirimicarb resistant preferred high sugar levels. In other meaning, the present study proved that dark morphs of the cotton aphid and light forms of the cowpea aphid were resistant to pirimicarb and this resistance was positively correlated with the levels of sugars in the plants. Therefore, plant breeders are requested to pay efforts in screening process of resistant plants to produce plants with low sugar contents to increase the effectiveness of pirimicarb against both species of aphids.