Four antibiotics were individually incorporated into holidic diets that were fed to the pea aphid, Acyrthosiphon pisum (Harris). Streptomycin and penicillin at 0.01% had little effect on growth, but reduced fecundity and survival. Chloromycetin and neomycin at 0.01% greatly reduced growth and survival, and aphids did not reach the adult stage. Higher concentrations (0.1%) of streptomycin and penicillin significantly reduced growth and survival, and no adults were produced if continued on penicillin. However, such a high concentration did not seem to inflict irrecoverable damages, since when aphids that were fed for 7 days on 0.1% streptomycin and penicillin were returned to antibiotic-free (control) diets they gained weight, reached maturity, and reproduced, although progeny survival was very low.Streptomycin appeared to be phagostimulatory, whereas penicillin and chloromycetin acted as feeding deterrents. First-instar larvae on the control diet, and on diets containing 0.1% streptomycin, penicillin, and chloromycetin in 24 h ingested 95.4, 120.8, 45.4, and 35.7 μg per aphid, respectively. It is suggested that these three antibiotics caused only partial damage to the symbiotes of the aphid, and that the poor growth, survival, and fecundity associated in the first generation with high concentrations of either penicillin or chloromycetin resulted mainly from a lower rate of diet intake.
Juvenile growth of provenances and open pollinated families of four Russian larch species (Larix Mill.) in Swedish field tests