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• Hastings, J
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Insects 2012, 3(1), 133-140; doi:10.3390/insects3010133

Article

Near-Optimal Foraging in the Pacific Cicada Killer Sphecius convallis Patton (Hymenoptera: Crabronidae)

Joseph R. Coelho ^1,* , Jon M. Hastings ²  and Charles W. Holliday ³

¹ Institute for Franciscan Environmental Studies, Biology Program, Quincy University, Quincy, IL 62301, USA ² Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA ³ Department of Biology, Lafayette College, Easton, PA 18042, USA

* Author to whom correspondence should be addressed.

Received: 1 January 2012; in revised form: 21 January 2012 / Accepted: 1 February 2012 / Published: 10 February 2012

(This article belongs to the Special Issue Feature Papers 2012)

Download PDF Full-Text [188 KB, uploaded 10 February 2012 09:22 CET]

Abstract: This study evaluated foraging effectiveness of Pacific cicada killers (Sphecius convallis) by comparing observed prey loads to that predicted by an optimality model. Female S. convallis preyed exclusively on the cicada Tibicen parallelus, resulting in a mean loaded flight muscle ratio (FMR) of 0.187 (N = 46). This value lies just above the marginal level, and only seven wasps (15%) were below 0.179. The low standard error (0.002) suggests that S. convallis is the most ideal flying predator so far examined in this respect. Preying on a single species may have allowed stabilizing selection to adjust the morphology of females to a nearly ideal size. That the loaded FMR is slightly above the marginal level may provide a small safety factor for wasps that do not have optimal thorax temperatures or that have to contend with attempted prey theft. Operational FMR was directly related to wasp body mass. Smaller wasps were overloaded in spite of provisioning with smaller cicadas, while larger wasps were underloaded despite provisioning with larger cicadas. Small wasps may have abandoned larger cicadas because of difficulty with carriage.

Keywords: wasp; optimal foraging; cicada; desert; insect; load carriage; flight; force

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