Nutritional stress and behavioural immunity of damselflies

Increased mortality in the presence of stress may result from stress-reduce d availability of energy for immune function, coupled with the presence of pathogens or parasites. We tested the hypothesis that stress reduces antipa rasite responses of damselflies Ischnura verticalis (Hagen) to their ectopa rasitic mites Arrenurus pseudosuperior (Marshall). Numbers of colonizing mi tes did not differ between nutritionally stressed and unstressed damselflie s. However, unstressed damselflies successfully removed more attached mites than nutritionally stressed host larvae. Furthermore, certain damselfly be haviours increased in the presence of nonfeeding mite larvae. Some of these behaviours were effective in defending against mites, but were reduced by nutritional stress. These results are-sufficient to explain inverse relatio ns found between damselfly condition and intensity of mite parasitism seen in nature, and are likely to be applicable to other host-ectoparasite assoc iations. (C) 2001 The Association for the Study of Animal Behaviour.