FITNESS COMPARISON BETWEEN CLONES DIFFERING IN THEIR ABILITY TO PRODUCE SEXUALS IN THE APHID RHOPALOSIPHUM-PADI

This study aimed at evaluating the intrinsic rate of increase (r(m)) o f clones of the cereal aphid Rhopalosiphum padi (L.) that differ in th eir ability to produce sexuals. The value of r(m) was measured for win gless parthenogenetic females in experiments conducted at two temperat ures (15 degrees C and 20 degrees C). We studied six holocyclic clones , five androcyclic clones and five anholocyclic clones and showed that life-cycle has no significant effect on the age at first reproduction , on fecundity nor on longevity. As a result there is no influence on (summer) fitness: on the one hand, holocyclic clones do not compensate their lower fitness in mild winters by a higher fitness during the su mmer. On the other hand, anholocyclic and androcyclic clones do not se em to obtain any advantage from living on a more restricted range of h osts: there appears to be no cost of polyphenism for holocyclic clones .