POLYPHENISM AND HOST-PLANT PREFERENCE IN THE BLACK BEAN, APHIS-FABAE SCOP

Field-collected and laboratory-reared aphids were offered the choice of larvipositing (parthenogenetic adults) or settling (oviparae and males) on either a detached, mature spindle leaf (Euonymus europaeus) or a germinating tick bean (Vicia faba). Alate fundatrigeniae showed no distinct preference for bean or spindle while the majority of other adult females (fundatrices, apterous fundatrigeniae, apterous and alate exules) larviposited on bean. Gynoparae showed a marked preference for larviposition on spindle, oviparae preferred to settle on spindle while males proved restless and preference could not be judged. Host-plant selection for larviposition could be modified hormonally. During their first, second and fourth stadia, gynoparae were reared on beans treated with juvenile hormone I or the juvenile hormone mimic, kinoprene. The resulting adults, which were devoid of any overt larval characters, showed differences in host-plant preference from untreated and solvent-treated controls. This finding suggests that juvenile hormone may have a role in alternative polyphenism associated with heteroecy i.e. the differences in host plant preference shown by alate exules and gynoparae.