Nocturnal host manipulation by nematomorphs is not synchronized with the lunar cycle

Many parasites manipulate host behavior by altering hosts’ phototaxis. At night, the lunar cycle shapes the light environment, raising the question of whether parasites manipulate their nocturnal hosts in response to this cycle. Nematomorph parasites induce their diurnal arthropod hosts to enter water by inducing positive phototaxis to light reflected from water surfaces. Here, we hypothesized that nematomorphs manipulate nocturnal camel crickets according to the lunar phase. Contrary to the hypothesis, camel crickets entered a pond with similar frequency on both new and full moon days. In addition, the number of camel crickets ingested by stream salmonids did not differ significantly between new and full moon days. These results imply that nematomorphs may have evolved mechanisms that are not strongly dependent on altering phototaxis when manipulating nocturnal hosts. This highlights the need to further investigate how parasites have evolved conserved and divergent manipulation strategies in heterogeneous light environments.