Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2005
Publication Date: 9/21/2005
Citation: Lorch, P.D., Sword, G.A., Gwynne, D.T., Anderson, G.L. 2005. Radiotelemetry reveals differences in individual movement patterns between outbreak and non-outbreak mormon cricket populations. Ecological Entomology. 30:548-555.
Interpretive Summary: The Mormon cricket is a flightless shield-backed katydid widely distributed throughout western North America. Outbreaks of this species can result in the formation of spectacular migratory bands that can be over 10 km long, several kilometers wide, contain dozens of insects per square meter, and travel up to 2.0 km per day. We used small radiotransmitters to compare the movement patterns of individual Mormon crickets in outbreak and non-outbreak populations. We found that that individuals in outbreak, migratory band-forming populations walk much greater distances per day relative to individuals in non-outbreak, non-band-forming populations. Insects in band-forming populations moved an average of 331 m/day with some individuals moving almost 2 km. On the other hand, insects in non-band-forming populations moved much less, an average distance of 0.66 m/day. We also observed distinct differences between the population types in their directionality. Non-band-forming insects did not move in any particular direction as a group, whereas the direction of movement of band-forming insects was similar among all the insects in a band and consistent across multiple days. When turns occurred, we found that Mormon crickets in migratory bands turn in a similar manner regardless of their position within the band. This suggests that the insects are either responding as a group to some large scale cue that influences their direction of movement such as wind, or possibly that they are simply responding to direction changes made by other insects in the band. This study forms the basis for ongoing work testing hypotheses about mass migrations in outbreak insect populations.
Technical Abstract: Outbreaks of insect pest populations are common and can have devastating effects on natural communities and on agriculture. Little is known about the causes of these outbreaks nor the causes of en masse migrations during outbreaks. We focus on flightless Mormon crickets (Anabrus simplex) a katydid species that forms large, dense, mobile groups (bands) during outbreak periods eating much of the vegetation in their path. We used radiotelemetric methods to measure differences in movement rate and directionality in outbreak and non-outbreak populations, testing the hypothesis that these populations differ. We show that daily individual movement in band-forming populations differs substantially from non-band-forming populations that are at much lower density. In addition to large differences in distances traveled (1.6 km as compared to 1 m) and rates of travel, we also provide evidence for collective movement among individual Mormon crickets traveling in migratory bands. Our data suggest that the direction of group movement may be influenced by local environmental conditions such as wind direction and movement of nearby band members. This work forms the basis for ongoing work testing hypotheses about mass migrations in outbreak populations.