Investment in immune function under chronic and acute immune challenge in an insect

In this paper we investigate the relationship between the chronic burden of mid-gut parasites (eugregarine trophozooites) and the effect of an acute h aemolymph challenge (a nylon insert) on two important insect immune effecto r systems (phenol oxidase (PO) and the encapsulation response) in a field-p opulation of damselflies. PO levels in the haemolymph, and the magnitude of the encapsulation response were maintained, regardless of chronic and subs equent acute experimental immune challenges. The maintenance of these effec tor systems is therefore probably an important life-history requirement in these damselflies. Investment in mid-gut PO levels was significantly negati vely related to the animal's chronic parasite burden after an acute experim ental challenge in the haemolymph, suggesting that maintaining PO levels ac ross two physiological compartments (haemolymph and mid-gut) is costly. The results suggest that the immune effector system activity in different phys iological compartments in an insect's body is affected by chronic parasite burdens in the face of the demands imposed by an acute immune insult.