REPRODUCTIVE EFFORT AND MATERNAL AGE IN ITEROPAROUS INSECTS USING APHIDS AS A MODEL GROUP

1. Life-history theory predicts that as the residual reproductive valu e of an organism declines its current investment in reproduction shoul d increase. This hypothesis has not been previously tested for insects . 2. The results of a laboratory study on the reproductive investment of the willow-carrot aphid, Cavariella aegopodii and the vetch aphid, Megoura viciae were compared with the predictions of the aphid optimal energy partitioning model. 3. The model's assumption that the fecundi ty function in aphids is triangular was supported. 4. As predicted by the model, the sizes of gonads decrease and those of the offspring inc rease with the age of the mother. 5. The large offspring born towards the end of a mother's life achieve a greater adult weight, mean relati ve growth rate and potential intrinsic rate of increase than the small offspring born early in a mother's life. The better performance of th e last born is a consequence of their large birth size. 6. The size of the offspring varies inversely and the reproductive investment positi vely with residual reproductive value. The increase in offspring size towards the end of a mother's life is a consequence of the time lag be tween ovulation and birth and the cessation of ovulation well before a mother dies. The excess of energy produced by the soma in old mothers is used to accelerate the growth rate of the remaining offspring. Thi s result can be extended to other groups that conform to the aphid mod el's assumptions.