the effect of hunger on foraging behavior of an aphid parasitoid, lysiphlebus fabarum (marshall) on aphis fabae scopoli

the black bean aphid, aphis fabae scopoli, is a major pest of broad bean, vicia faba l. and sugar beet, beta vulgaris l., the most abundant parasitoid of a. fabae in agroecosystems is lysiphlebus fabarum (marshall), a multivoltine species with mainly thelytokous reproduction in central europe. since l. fabarum females mimic ants to obtain honeydew directly from aphids it was reasoned that a female's hunger level could influence her proportional time allocation to various behaviors associated with aphid exploitation. to test this, l. fabarum females were released individually onto bean leaf disks infested with a. fabae and continuous observations made. the females’ proportional time allocations were then recorded. furthermore, instances of aphid defensive behaviors including kicking, raising and swiveling the body, releasing the plant and escaping from attack, as well as attempts to smear the attacker with cornicle secretions were numerically assessed. hungry females spent 3.6 times longer in host patches (leaf disks with 15 second-third instar of a. fabae) than did females fed diluted citrus honey prior to testing, but there were no differences observed among number of aphids parasitized. all the assessed measured distinct behaviors were higher for unfed females than for fed ones. because of the large effect of treatment on patch residence time, the incidence or duration of various behaviors was expressed as a fraction of patch residence time and then re-analyzed. hungry females spent proportionally more of their time resting and antennating aphids with proportionally less time spent in searching, abdominal bending and probing aphids. a significantly smaller proportion of aphids kicked and escaped from attack following encounters with hungry females than when encountered with satedly fed females.