Impact of parasitism by larval Limnochares aquatica (Acari: Hydrachnidia; Limnocharidae) on juvenile Gerris comatus, Gerris alacris, and Gerris buenoi (Insecta: Hemiptera; Gerridae)

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Abstract
Laboratory-reared first-instar juvenile Gerris comatus Drake and Hottes, Gerris alacris Hussey, and Gerris buenoi Kirkaldy were exposed to larval Limnochares aquatica (L.). Development and mortality of parasitized juvenile water striders were monitored and compared with those of unparasitized insects. Duration of infestation was from 6 to 13 days during which surviving hosts moulted several times, with engorging larvae transferring to the teneral host during the moulting process. Most mites dropped off the host during the host''s second instar, and all mites were off the host by the host''s fourth instar. Parasitism by larval mites significantly increased mortality, duration of instars, and variance in age at first moult for parasitized water striders. Mortality and duration of first instars were directly correlated with number of mites per host. Parasite-induced mortality was not evident until 2 days after attachment of mites, and almost all mortality occurred within the host''s first instar. Gerris comatus and G. alacris apparently did not differ in response to parasitism; however, G. buenoi showed greater mortality than the other gerrid species when carrying comparable numbers of mites. The effects of parasitism on juvenile water striders within natural populations are predicted to be severe, and would reduce recruitment while also increasing variation in age structure.