Development responses of symbiotic and aposymbiotic weevils Sitophilus oryzae L. (Coleoptera,curculionidae) to a diet supplemented with aromatic amino acids

Developmental times of symbiotic and aposymbiotic strains of the rice weevil Sitophilus oryzae were compared, in response to changes in concentration of phenylalanine or tyrosine in whole wheat flour pellets. Aposymbiotic insects were shown to require more aromatic amino acids than symbiotic insects, since a very low supply (0.1%) resulted in faster growth (11%). Incorporation results of [³H]-tyrosine during the larval and pupal stages indicated that total tyrosine intake was lower in aposymbiotic insects, but the incorporation into the cuticle of both strains did not significantly differ. It is suggested that the slower growth rate of weevils without symbiotes is due, in part, to a less efficient utilization of exogenous tyrosine (in the food) and to a lack of endogenous tyrosine (supplied by the symbiotes).