Color Polymorphism does not Affect Species Diagnosis of the Melon Aphid, Aphis gossypii (Hemiptera: Aphididae)

The melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae) has become a serious pest of wide spectrum of crops and is considered to be a potential vector of numerous plant pathogenic viruses worldwide. This pest exhibits color polymorphism in which dark green, pale green and yellow forms exist within a single colony on the same plant and also on different host plants. The co-occurrence of different color forms makes species diagnosis and identification of cryptic species difficult, while they have immense importance in quarantine and biosecurity. Therefore, establishing a tool that facilitates quick and accurate identification of A. gossypii is an urgent need. Molecular diagnosis is the most appropriate and becomes handy because it is independent of sex, polymorphism and life stage, and could be effectively used by person with no or little knowledge in aphid taxonomy. In this study, two mitochondrial markers i.e. cytochrome oxidase subunit gene I (COI) and the tRNA-leucine + cytochrome oxidase subunit gene II (tRNA/COII) were tested for species diagnosis. Alignment of partial COI and tRNA/COII sequences from various color forms of A. gossypii collected from 6 different host plants viz., cotton, okra, cucumber, watermelon, aubergine and chili pepper revealed maximum sequence identity (99.7% and 99.4%) suggesting that molecular identification is independent of the color polymorphism in this species. Thus, it is concluded that, color polymorphism does not affect species diagnosis of A. gossypii. The study has unambiguously proved the utility of COI and tRNA/COII for a quick and accurate diagnosis of A. gossypii, which is a critical factor in elucidating virus transmission and implementing biological control.