Abstract
Factors affecting the ecology of a large population of Pacific cicada killers (Sphecius convallis) occupying a field of mine tailings in Ruby, AZ, were examined. Burrows were quite dense in certain areas around the periphery of the mine tailings, but were dispersed randomly within these areas. Approximately 1600 females (based on burrow counts) and 2500 males (based on mark-recapture) were recorded, yielding a total population estimate of 5000–6000 adults. Female wasps were able to dig much more rapidly in the mine tailings than their congeners S. speciosus in soils from PA, suggesting that the habitat suitability was a large factor in this robust population. Provisioning rate was comparatively slow, however, suggesting that cicada abundance in that year was not a contributor to the high population density. The presence of a sap-producing tree may have eased the energetic and thermoregulatory demands of the wasps. Although excavations revealed that the number of burrows and cells could easily maintain the population size, the lack of cicadas probably resulted instead in a population crash the following season.
Highlights
IntroductionFour species of cicada killers (genus Sphecius) occur in North America (Coelho et al 2011)
Pacific cicada killers (Sphecius convallis Patton, 1879; Hymenoptera: Crabronidae) have nested at Ruby, Arizona (Santa Cruz County) probably at least since 1940, and perhaps since the sandy galena ore mine tailings were deposited in the valley by the operations of the Montana and Ruby mines between the late 1800s and the 1930s (Ring et al 2005)
A total of 1588 burrows were recorded for the high density sites alone on the dates we recorded them
Summary
Four species of cicada killers (genus Sphecius) occur in North America (Coelho et al 2011). Pacific cicada killers (Sphecius convallis Patton, 1879; Hymenoptera: Crabronidae) have nested at Ruby, Arizona (Santa Cruz County) probably at least since 1940, and perhaps since the sandy galena ore mine tailings were deposited in the valley by the operations of the Montana and Ruby mines between the late 1800s and the 1930s (Ring et al 2005). Their presence was recorded in a documentary film (BBC 1993), which prompted us to visit the site. Many prey cicadas are stolen by birds and conspecific females, which enter the burrows of others and lay eggs on their alreadyprovisioned cicada (Coelho et al 2019)
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