BEHAVIOR, CHEMICAL ECOLOGY Responses of Ornithonyssus sylviarum (Acari: Macronyssidae) and Menacanthus stramineus (Phthiraptera: Menoponidae) to Gradients of Temperature, Light, and Humidity, With Comments on Microhabitat Selection on Chickens

Responses of the northern fowl mite (NFM), Ornithonyssus sylviarum (Canestrini & Fanzago) (Acari: Macronyssidae), and the chicken body louse (CBL), Menacanthus stramineus (Nitzsch) (Phthiraptera: Menoponidae), to variation in temperature, light, and humidity were assessed in bioassays. The location on a continuous thermal gradient atwhich each ectoparasite arrested was recorded and analyzed. NFM adults arrested at an average temperature of 30.09 0.34 C. Adult CBL and Þrst-instar CBL nymphs arrested at 33.69 0.20 C and 34.99 0.26 C, respectively. Groups of each ectoparasite were placed into clear glass vials (n 10/vial) with one half shaded, and vials wereexposed to three light levels, as follows:high(200 molm s ), low(4 molm s ), andnearly no light (0 molm s ). The vial cap edges provided an opportunity to assess the interactive effect of light with harborage. NFM avoided light and sought harborage. In low light, the harborage preference overrode the tendency to avoid light. CBL avoided the harborage and showed a minimal preference for light. A four-level humidity gradient was established in two separate experimental arenas forNFMandCBL. Trials were run in ambient light (4 molm s ) for theNFMand in nearly no light for the CBL. The NFM gradient used 38 2%, 54 7%, 73 3%, and 90 4% RH, whereas theCBLgradientused42 5%, 48 7%, 63 4%, and73 5%RH.NFMshowednohumidity response in the walking bioassay, but the CBL settled at the lowest humidity level. Temperature and humidity on different hen body regions were related to the bioassay results and observed on-host ectoparasite distributions.