Active defence of herbivorous hosts against parasitism: Adult parasitoid mortality risk involved in attacking a concealed stemboring host

Phytophagous insects have several defence strategies to defend themselves a gainst attack by parasitic wasps. Larval lepidopteran hosts can defend them selves actively to prevent oviposition by the parasitoid. Among the aggress ive kinds of behaviour exhibited by hosts against parasitoids are violent w riggling, biting and spitting. The behaviour of the braconid parasitoid Cot esia sesamiae attacking stemboring larvae inside their feeding tunnel in th e plant stem was investigated in maize and sugarcane stem pieces and transp arent artificial tunnels. Attacking a defending stemborer host inside the c onfined space of a tunnel was shown to be risky for the female parasitoid. A considerable proportion (25%) of female wasps were killed in their attemp t to attack the spitting and biting host. No difference was found in the be haviour of C. sesamiae attacking the suitable host Sesamia calamistis or th e unsuitable host Eldana saccharina. The consequences of this high mortalit y risk involved in each host attack is discussed in relation to the ecology of the parasitoid.