Nictation Behaviour and Its Ecological Implications in the Host Search Strategies of Entomopathogenic Nematodes (Heterorhabditidae and Steinernematidae)

Abstract

[Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) are insect parasites that appear to use both cruising and ambushing search strategies. Cruising species Heterorhabditis bacteriophora, Steinernema feltiae, and S. glaseri spent more time crawling (88.8, 80.3, and 92.5% of observation period, respectively) and therefore traveled farther (22.4, 18.6, and 24.3 mm, respectively) and searched a larger area (18.3, 13.7, and 26.6 mm2, respectively) than ambushing species. Ambusher species S. carpocapsae and S. scapterisci traveled shorter distances (4.8 and 4.7 mm, respectively) and searched smaller areas (3.0 and 2.5 mm2, respectively) because they spent most of the observation period nictating (77.5 and 78.2%, respectively). Nictating infective juveniles raise greater than 95% of their body off the substrate and maintain a straight posture. A nictating species S. carpocapsae was up to 43 times as effective at finding mobile insect hosts compared to a non-nictating species H. bacteriophora. When unable to nictate host-finding of mobile insects declined from 35.7±7.19 to 3.9±1.11 infective juveniles per host. Nictation, by reducing the surface tension forces holding the nematode to the substrate, can increase the nematodes ability to attach to passing insects. S. carpocapsae also tended to search more effectively along a surface than through a matrix. Although entomopathogenic nematodes have a broad potential host range, differences in search behavior may result in a narrower actual host range. Ambushers being more specialized for mobile insects on the soil surface and cruisers for more sedentary and/or subterranean insects., Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) are insect parasites that appear to use both cruising and ambushing search strategies. Cruising species Heterorhabditis bacteriophora, Steinernema feltiae, and S. glaseri spent more time crawling (88.8, 80.3, and 92.5% of observation period, respectively) and therefore traveled farther (22.4, 18.6, and 24.3 mm, respectively) and searched a larger area (18.3, 13.7, and 26.6 mm2, respectively) than ambushing species. Ambusher species S. carpocapsae and S. scapterisci traveled shorter distances (4.8 and 4.7 mm, respectively) and searched smaller areas (3.0 and 2.5 mm2, respectively) because they spent most of the observation period nictating (77.5 and 78.2%, respectively). Nictating infective juveniles raise greater than 95% of their body off the substrate and maintain a straight posture. A nictating species S. carpocapsae was up to 43 times as effective at finding mobile insect hosts compared to a non-nictating species H. bacteriophora. When unable to nictate host-finding of mobile insects declined from 35.7±7.19 to 3.9±1.11 infective juveniles per host. Nictation, by reducing the surface tension forces holding the nematode to the substrate, can increase the nematodes ability to attach to passing insects. S. carpocapsae also tended to search more effectively along a surface than through a matrix. Although entomopathogenic nematodes have a broad potential host range, differences in search behavior may result in a narrower actual host range. Ambushers being more specialized for mobile insects on the soil surface and cruisers for more sedentary and/or subterranean insects.]