Host recognition cues of the granary weevil parasitoid Lariophagus distinguendus

Host recognition was examined in Lariophagus distinguendus (Forster), a par asitoid of larvae of the granary weevil Sitophilus granarius (L.) that live endophytically in wheat grains. On encountering a grain infested with S. g ranarius, females of L. distinguendus behave in a set sequence. First they show antennal drumming on the grain, second they tap with the tip of the ab domen on the grain surface, third they drill into the grain and then insert their ovipositor. Bioassays revealed that drumming and drilling was stimul ated by non-volatile chemicals present on the grain-host complex. Host faec es and herbivore damaged grain material stimulated the most activity, follo wed by artificially damaged grain, and healthy grain. This is the first rep ort on non-volatile chemicals released from herbivore-damaged seeds as sign als for foraging parasitoids. Volatile chemicals from the faeces alone were not active. Experiments on the use of physical cues revealed that the pres ence of a three-dimensional structure increased the response towards chemic als from the faeces. The shape (ovoid or rectangular solid) and colour (bro wn or white) of the structure had no impact. Thus, physical cues alone were insufficient to stimulate host recognition behaviour, but acted by increas ing the response towards the chemical stimuli.