Development and Reproduction of Two Color Forms of English Grain Aphid (Homoptera: Aphididae)

Abstract

The life cycle of apterous and alate viviparae of pink and green color forms of the English grain aphid, Sitobion avenae (F.), were compared at 20 ± l°C and a photoperiod of 14:10 (L:D) h, using individually caged aphids that were examined daily on ‘Clintland 64’ oat, Avena sativa L. Two studies were conducted, using 22 replicates with apterous and alate S. avenae , and 132 replicates with only apterous forms. Alate aphids had a greater prereproductive period than apterous aphids, probably in part because their metabolism was directed towards wing development before reproduction. Apterous pink aphids had a shorter reproductive period than all other forms. This, together with their higher intrinsic rate of increase (rm), may represent an advantage over green aphids for colony growth, although this advantage may be reduced because alate pink aphids had the smallest rm of the aphid forms. Alate aphids tended to have a longer postreproductive period. The longevity of apterous pink aphids was shorter compared with the other forms, but this was compensated by their greater rm. The percentage of alate aphids was slightly larger in the pink (17.16%) than in the green form (14.97%), which may help the dispersal of the pink genotype over time. All parameters of the life cycle, except the reproductive period, showed differences between apterous green and pink S. avenae . The pre-, post-, and reproductive periods were shorter for apterous pink aphids, which was reflected in a shorter longevity, compared with apterous green and alate pink and green forms. However, apterous pink aphids had more progeny, which meant a larger rm, than green aphids. Variations in the life cycle like those between the green and pink forms observed in this study may occur among other clones of S. avenae (and possibly in other aphid species). Aphid studies should use >1 clone per species to obtain representative data of average populations.