DEVELOPMENT AND REPRODUCTION OF 2 COLOR FORMS OF ENGLISH GRAIN APHID (HOMOPTERA, APHIDIDAE)

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 +/- 1 degrees C and a photoperiod of 14:10 (L:D) h, using indiv idually caged aphids that were examined daily on 'Clintland 64' oat, A vena sativa L. Two studies were conducted, using 22 replicates with ap terous and alate S. avenae, and 132 replicates with only apterous form s. Alate aphids had a greater prereproductive period than apterous aph ids, probably in part because their metabolism was directed towards wi ng development before reproduction. Apterous pink aphids had a shorter reproductive period than all other forms. This, together with their h igher intrinsic rate of increase (r(m)), may represent an advantage ov er green aphids for colony growth, although this advantage may be redu ced because alate pink aphids had the smallest r(m) of the aphid forms . Alate aphids tended to have a longer postreproductive period. The lo ngevity of apterous pink aphids was shorter compared with the other fo rms, but this was compensated by their greater r(m). The percentage of alate aphids was slightly larger in the pink (17.16%) than in the gre en form (14.97%), which may help the dispersal of the pink genotype ov er time. All parameters of the life cycle, except the reproductive per iod, 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 apte rous green and alate pink and green forms. However, apterous pink aphi ds had more progeny, which meant a larger r(m), than green aphids. Var iations 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 pe r species to obtain representative data of average populations.