RESOURCE TRACKING IN APHIDS - PROGRAMMED REPRODUCTIVE STRATEGIES ANTICIPATE SEASONAL TRENDS IN HABITAT QUALITY

Most aphids show cyclical parthenogenesis, have short generation times and complete several generations each season. Two hypotheses have bee n proposed to account for the adaptive seasonal trends observed in the reproductive strategies of aphids. Firstly, individuals of each gener ation modify their reproductive strategy in direct response to the con ditions they experience during their development. Secondly, the reprod uctive strategies of the different generations are to a large extent p rogrammed and anticipate seasonal trends in habitat quality. These hyp otheses were tested by rearing individuals of three generations of the host-alternating willow-carrot aphid, Cavariella aegopodii, on both w illow and carrot. This revealed that the way this aphid allocates reso urces to gonads and lipid reserves is independent of an aphid's weight and the host plant on which it is reared. In addition each generation shows a specific relationship between offspring size and adult size, which tends to keep the absolute investment in individual offspring re latively constant from generation to generation, inspite of the big di fferences in adult size between generations. That is, through programm ed allometric engineering aphids anticipate the predictable seasonal t rends in habitat quality and so more closely track their resources, in vesting relatively more in gonads when food quality is high and relati vely more in lipoidal reserves when food quality is poor.