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ARS Home » Plains Area » Sidney, Montana » Northern Plains Agricultural Research Laboratory » Pest Management Research » Research » Publications at this Location » Publication #322749
Title: Loss of safety in numbers and a novel driver of mass migration: Radiotelemetry reveals heavy predation on a band of Mormon crickets

Author
item Srygley, Robert
item LORCH, PATRICK - Kent State University

Submitted to: Proceedings of the Royal Society of London: Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2016
Publication Date: 5/4/2016
Publication URL: http://handle.nal.usda.gov/10113/62806
Citation: Srygley, R.B., Lorch, P.D. 2016. Loss of safety in numbers and a novel driver of mass migration: radiotelemetry reveals heavy predation on a band of Mormon crickets. Royal Society Open Science. 3(5):160113. doi:10.1098/rsos.160113.

Interpretive Summary: Mormon crickets and locusts are model organisms for understanding collective motion in animals. Grouping provides safety from predation, but grouping also has costs, including increased competition for food and risk of cannibalism. We investigated predation by digger wasps on collectively moving Mormon crickets as an additional cost to grouping. By radio-tracking migrating Mormon crickets released over three days, we found that digger wasps prey heavily on aggregated Mormon crickets leading to loss of safety from predation. Palmodes laeviventris paralyzed and buried 42% of tagged females and 8% of the males on the final day of tracking. A preference for females to provision their offspring make the digger wasps particularly effective at controlling Mormon cricket populations. The greater fat content and larger size of female Mormon crickets compared to males is likely to improve survival of wasps during diapause. Wasps may play an important role in causing density declines leading to periods where Mormon crickets are only found sporadically throughout their range. Wasp predation represents a cost to collective movement with results from this study suggesting that avoidance of this specialized predator should strongly select for Mormon cricket emigration from natal sites, adding to the threat of cannibalism as selective forces spurring collective motion.

Technical Abstract: Coordinated movement of animals is a spectacular phenomenon that has received much attention. Experimental studies of Mormon crickets and locust nymphs have demonstrated that collective motion can arise from cannibalism that compensates for nutritional deficiencies arising from group living. Grouping into migratory bands confers protection from predators. By radio-tracking migrating Mormon crickets released over three days, we found that specialized, parasitoid digger wasps (Sphecidae) respond numerically and prey heavily on aggregated Mormon crickets leading to loss of safety in numbers. Palmodes laeviventris paralyzed and buried 42% of tagged females and 8% of the males on the final day of tracking. Risk of wasps and Mormon crickets hatching on the same site is high and may drive nymphal emigration. A preference to provision offspring with adult female Mormon crickets can be explained by their greater fat content and larger size compared to males, improving survival of wasps during diapause.