The feeding, growth and reproduction of Aphis fabae Scop. on Viciu fuba under experimental conditions

SUMMARY The total amount of sap ingested by individual larvae and adult (apterous virgino-parae) of Aphis fabae on field beans was estimated by adding the weights of honeydew excreted and of water lost by evaporation to increases in body weight during growth and to the weight of larvae born throughout the lives of the adult insects. The quantity of respiratory gases was ignored. Temperature and lighting were kept constant; air humidity was kept high to lessen evaporation, and air movements were eliminated. A machine was made to collect simultaneously the excreta of ten individual aphids to record their total daily excreta continuously from birth to death. Honeydew was also collected daily in mineral oil from other aphids of the same age on similar plants, to estimate the size of the droplets. The mean excretion rate was estimated from the product of the mean frequency of excretion and the mean size of the droplets. The reproductive rate, fecundity and length of reproductive and post-reproductive life of the adult aphids were also recorded. The larva ingested about 3?5-45 mg. of sap in a life of 7 days and the adult about 30 mg. during a reproductive life of 21 days; only about 10% was used for growth and reproduction. The excretion of the adult rose to a maximum of 30?40 drops per day on the third day of adult life and then declined, apparently because of changes within the aphid itself, for when the insects were transferred to fresh plants the excretion continued to decrease. The rate of feeding, which is about equal to the rate of excretion, therefore also decreased as the insect aged but its rate of reproduction remained fairly steady for about 16 days. The swelling of the abdomen and the slight increase in weight during the post-reproductive life of about 2 weeks suggested that, although excretion had stopped, small amounts of sap continued to be ingested. The aphids ingested about the same amount of sap on two varieties of field bean but were significantly more fecund on one than on the other, a difference probably attributable to differences in the quality of the sap of the two varieties.