A parasite's modification of host behavior reduces predation on its host

Area of Science:

• Ecology
• Parasitology
• Behavioral Ecology

Background:

• Parasite manipulation of host behavior often increases predation, facilitating parasite transmission.
• However, reduced predation on parasitized hosts is theoretically predicted but rarely observed.

Purpose of the Study:

• To investigate how gregarine endosymbionts (Ascogregarina barretti) affect the predation vulnerability of Aedes triseriatus mosquito larvae.
• To determine if parasite infection alters host behavior in response to predation cues.

Main Methods:

• Compared mortality rates of parasitized and unparasitized Aedes triseriatus larvae exposed to the predatory larva Toxohrynchites rutilus.
• Recorded and analyzed larval behavior, including thrashing frequency and location within microcosms, under different treatment conditions.

Main Results:

• Gregarine infection significantly reduced larval mortality when predators were present; the parasite alone did not affect mortality.
• Infected larvae exhibited reduced thrashing and increased use of refuge areas compared to uninfected larvae.

Conclusions:

• Gregarine parasites can decrease predation on their mosquito hosts, potentially acting as mutualists in predator-rich environments.
• This study highlights a higher-order interaction where a third species (predator) alters the host-parasite relationship.