No evidence of bacterial symbionts influencing host specificity in Aphis gossypii Glover (Hemiptera: Aphididae)

The cotton-melon aphid, Aphis gossypii Glover, is a polyphagous insect pest with many host-specialized biotypes, such as Cucurbitaceae- and Malvaceae-specialized (CU and MA) biotype. Bacterial symbionts were reported to determine host range in some aphids. Whether this is the case in A. gossypii remains unknown. Here, we tested host specificity of CU and MA biotype and compared host specificity between wingless and winged morph within the same biotype, and analyzed the composition of bacterial symbionts. The reproduction of CU and MA biotype reduced by 66.67% and 82.79% respectively on non-native hosts, compared with that on native hosts. The composition of bacterial symbionts was not significantly different between CU and MA biotype, with Buchnera abundance >95% in both biotypes. While, winged morph produced significantly more nymphs than wingless morph on non-native hosts, and Buchnera abundance in winged morph was only about 10% of that in wingless morph. There seemed to be a relationship between Buchnera abundance and host specificity. We regulated Buchnera abundance by temperature and antibiotics, but did not find that low Buchnera abundance resulted in high reproduction on non-native hosts. We conclude that host specificity of A. gossypii is not controlled by specific bacterial symbionts or by Buchnera abundance.