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Loss of safety in numbers and a novel driver of mass migration: radiotelemetry reveals heavy wasp predation on a band of Mormon crickets

Srygley, Robert B., Lorch, Patrick D.
Royal Society Open Science 2016 v.3 no.160113 pp. 1-8
Anabrus simplex, Sphecidae, adults, animals, cannibalism, diapause, females, hatching, lipid content, locusts, males, migratory behavior, nutrient deficiencies, nymphs, parasitoids, predation, predators, progeny, radio telemetry, risk, survival rate
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.