The effects of Plagiorchis noblei (Trematoda: Plagiorchiidae) metacercariae on the behavior of Aedes aegypti larvae

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Abstract
Third-instar mosquito larvae (Aedes aegypti (L.)) infected with the metacercariae of the digenean Plagiorchis noblei Park exhibited significant behavioral changes. Larvae infected with more than three metacercariae were less active, spent more time suspended from the surface of the water, and spent less time in the bottom half of the water column than did uninfected control larvae. In contrast, larvae infected with one or two metacercariae were more active and spent less time suspended from the surface of the water. Such lightly infected larvae spent more time in the bottom half of the water column than the more heavily infected larvae. Since cercariae of P. noblei generally settle to the bottom of the water column, lightly infected larvae thus may be rendered more susceptible to superinfection. In contrast, heavily infected larvae may be removed from further exposure. Furthermore, heavily infected larvae may be more susceptible to surface-feeding predators. These behavioral changes of the insect host may facilitate the transmission of P. noblei both to the second intermediate and definitive host.