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Sphecius grandis

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Sphecius grandis
Two Sphecius grandis wasps mate (male above, female below), in Big Bend, Texas.
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Insecta
Order:
Hymenoptera
Family:
Crabronidae
Tribe:
Gorytini
Genus:
Sphecius
Species:
S. grandis
Binomial name
Sphecius grandis
(Say, 1823)[1]
Synonyms

Stizus grandis (Say)

Sphecius grandis, also called the western cicada killer, is a colony-forming species of cicada killer wasp (Sphecius). The western species shares the same nesting biology as its fellow species, Sphecius speciosus (eastern cicada killer).[2] S. grandis, like all other species of the genus Sphecius, mainly provide cicadas for their offspring.[2] They are colonial and mate and brood once in a year, in July and early August.[3] The wasp is on average two inches in length and is amber-yellow with yellow rings on the abdomen.[4]

The Sphecius genus is not habitually aggressive and save their venom for cicadas which they paralyze and take back to their nests.[4] The female catches around four or more cicadas for provisioning, places them in her brood cell and then proceeds to lay an egg in the cell.[4] The species is endemic to Central America and the Western United States,[5] and is found at a higher mean altitude that other species of Sphecius.[6] The males emerge earlier than females,[3] but generally die after only a couple of days.[4]

Identifying and differentiating from other species has been found to be difficult.[7] At first the method to tell between S. grandis and S. convallis was to compare the colour of the gastral tergites, S. grandis was originally thought to have yellow markings on all five gastral tergites and S. convallis to have three markings, but this was found to be inadequate.[7] A new method was recently devised which allowed identification through examination of the coloration of the tergite markings in the case of an anomaly.[7]

Taxonomy

The western cicada killer was first described by American naturalist Thomas Say in 1824 as Stizus grandis. Its species name is the Latin adjective grandis meaning "large". It is one of five species of the genus Sphecius in North America.[7] The species was collected by D. Maddox on September 8, 1957, in Madera Canyon, Arizona and correctly identified by Charles W. Holliday.[8]

More recently, it has been suspected that the western cicada killer represents more than one species.[9] It co-occurs with the eastern cicada killer (S. speciosus) and Pacific cicada killer (S. convallis) at Big Bend National Park in Texas.[9] There the three wasps hunt and nest in the same locales, and the eastern and western cicada killers hunt the same cicada species. Analysis of mitochondrial DNA showed that there were two divergent clades each within the western and pacific cicada killers, and that one clade of each were closely related to each other. This was possibly as a result of hybridization between them. The two populations of the western cicada killer appeared to be split by the Rocky Mountains, with one occurring mainly to the south and east, the other to the west.[9]

Description

At around 5 cm (2 in) in length, the western cicada killer is very similar to its eastern cousin, Sphecius speciosus, with amber stripes and a yellow abdomen.[4] On average, female forewing length lies between 25 and 30 mm.[2] Females are larger than males and live for a long enough time to produce a brood in a year, whereas the males die within only a few days, with enough time to impregnate a female.[4] In Steven J. Phillips' book A Natural History of the Sonoran Desert, he referred to them as superficially resembling "huge yellowjackets or hornets" and stated that they are "powerful fliers with compound eyes".[10] On average, males, far smaller than females, weigh 95 mg and females weigh 256 mg.[11] It is thought that this weight difference is to account for the additive weight of having ovaries, developing eggs and to carry nutritional reserves.[12] Despite this disproportionate ration, the flight muscle mass comparative to body mass was the same for both sexes.[12]

Identification

Distinguishing S. grandis from the other four New World species (S. convallis, S. hogardii, S. speciousus, S. spectabilis) of the genus Sphecius has been found to be difficult.[7] The female S. convallis was originally determined from the female S. grandis by the yellow marks from the first to third gastral tergites on S. convallis and yellow marks on all tergites for S. grandis.[7] However this was found to be insufficient because the positions of the markings can vary through different wasps of the same species.

A new key was devised in 2004, by Charles W. Holliday and J. R. Coelho, to identify and differentiate between Sphecius species.[7] In the experiment, they studied 4,451 wasps among the five New World species,[7] and came to the conclusion that the female S. convallis wasps examined had 98% yellow markings on gastral tergites one to four or less and S. grandis had 98% yellow markings from tergites one to five or greater.[7] The 2% percent of S. grandis that overlapped with S. convallis were determined by density of the punctation of the first tergite against the second.[7] The markings on S. grandis males were found to be the same as on females.[7]

Thermoregulation

It has been found that the western cicada killer wasp is capable of thermoregulation which enables them to hunt for cicadas during the day.[13] A study by Quincy University showed that during territorial patrolling the species had a high and regulated thorax temperature.[14] Experiments found that the wasp has the ability to move shift heat from its thorax to its abdomen and that the abdomen is generally kept colder than the thorax.[14] Dead wasps that were placed in the sun reached lethally high temperatures when compared to nearby plants.[14]

Life cycle

Birth, emergence and mating

After hatching, the offspring feed on the tissue of the cicadas provided by their mother. Males emerge before females and both genders are sexually receptive from emergence in July to early August.[3] Famed English naturalist Charles Darwin postulated that the pattern of male emergence before females evolved by natural selection to improve the chances of the male mating.[3] The timing of the emergence of females has evolved to correspond with the similar emergence of the cicada species of the area, Tibicen duryi and T. parallela, which they hunt for the provisioning of their nests.[3] Many have yellow markings located on their tergites (dorsal portion), although some have been found only from the first to fifth tergites.[7]

Sphecius speciosus (eastern cicada killer) shares many behavioural similarities to Sphecius grandis.

Because males emerge earlier than females, the males compete for mating territories surrounding the nests in which the females are located. During a fight, the males risk damaging the wings or their appendages by butting and grappling.[15] Another defence technique is to grab another male and carry it high into the air, which is thought to be a demonstration of strength.[15] A successful defence increases the chances that they pass on their genes.[3] As a general rule, the larger the male the more predominant he is in battles.[16] Age influences the success in the defense and secutity of territory.[17] The younger the wasp the greater chance of a successful takeover of territory.[17] Some small males even engage in non-territorial mating tactics.[17]

As females are receptive on emergence, a lately emerging male will likely not get the chance to mate and die within only a few days.[3] On female emergence from the nest, the female does not choose her mate, but instead copulates with the first ready male counterpart of its species that she finds.[3] Once the female has mated, she rebuffs all advances by other wasps.[18] The low fecundity of the females means that additive mating would not increase the chances of successful birth.[18]

Nesting and perching

Males perch after emerging from their nest. They pick out an area close to a nest with females inside and guard the territory around it so as to have a better chance of mating.[3] They tend to perch on many different substrates such as stumps, pebbles, wood, weeds, grass blades and low tree branches.[19] Males assume an alert posture, ready for a challenge from another male, or from a predator.[19] One study by a behavioural ecologist, John Alcock, showed that a large majority of the marked wasps returned to the same perch day after day, and two males swapped between two different sites.[19] The species rarely perches on the ground.[14]

All cicada killers are ground-nesting insects and nests can range from one to a group of hundreds of wasps.[9] Their tunnel is mainly made with sandy soil, frequently found under sidewalks.[20] Approximately 90% of its life is spent underground as a larva.[21]

Feeding and hunting habits

Sphecius grandis has very similar nesting and feeding habits to other members of its genus, most notably Sphecius speciosus.[2][3] As with S. speciosus,[22] the female hunts for cicadas, helped by the calls of the males,[20] paralyzes the insect by piercing the central nervous system with her stinger,[20] and drags the cicada back to her nest to place in a brood cell in which she eventually lays one egg per cell.[2] Females carry cicadas that are on average 88% higher than her own body mass.[12] It has also been hypothesized that cicada killers may have the ability to capture cicadas mid-flight.[12] There are approximately four cicadas to each brood cell.[2] When the larvae hatch, the cicada provides nutrition for the offspring.[2]

The wasps more prevalently hunt for female cicadas because they have more consumable tissue, but male cicadas are easier to locate which explains the systemic bias towards male kills.[23] They chiefly hunt for Tibicen duryi and T. parallela.[24] Cicada killers are capable of thermoregulation, which allows them to hunt for cicadas during the day, when they are most prominent.[13] The species is mostly harmless to humans.[20] Some males when emerging early fly into the trees to feed on sap,[19] and the species has been known to feed on nectar.[18]

Geographical distribution

Western cicada killers are found at a higher altitude than most other Sphecius species and share sympatry with the species S. convallis and S. speciosus, even though S. grandis are on average found at higher altitudes than S. convallis.[6] A study showed that the mean elevation for S. grandis was 755 ± 23.3, compared with the lower results of S. speciosus (219 ± 4.7), S. convallis (582 ± 30.9) and S. hogardii (18 ± 5).[6] The species is found from Central America to the Western United States.[5] S. grandis are the only cicada killers to be found in Utah and are most commonly found in riparian zones.[6] The species has been observed in such places in Mexico as Baja California Norte, Baja California Sur, Coahuila, Nuevo Leon, Tamaulipas and Yucatán and also in Granada (Nicaragua), Guanacaste (Costa Rica) and Honduras.[6]

References

  1. ^ Víctor, Jorge (2007). "Sphecidae y Crabronidae (Hymenoptera) – De algunos Municipios del Centro y Sur de Tamaulipas, México" (PDF). Acta Zoológica Mexicana. 23 (3): 35–48.
  2. ^ a b c d e f g Hastings, Jon (1986). "Provisioning by female Western cicada killer wasps, Sphecius grandis (Hymnoptera: Sphecidae): influence of body size and emergence time on individual provisioning success". Journal of the Kansas Entomological Society. 59 (2): 262–268. JSTOR 25084766. {{cite journal}}: Unknown parameter |month= ignored (help)
  3. ^ a b c d e f g h i j Hastings, Jon (1989). "Protandry in western cicada killer wasps (Sphecius grandis, Hymnoptera: Sphecidae) and empirical study of emergence time and mating opportunity". Behavioral Ecology and Sociobiology. 25 (4): 255–260. JSTOR 4600338. {{cite journal}}: Unknown parameter |month= ignored (help)
  4. ^ a b c d e f "Wasps (Order: Hymenoptera) – Robust Yellow Group". Chihuahuan Desert Nature Center and Botanical Gardens. Retrieved August 11, 2011.
  5. ^ a b Evans (2007), p. 34
  6. ^ a b c d e Coelho, Joseph R.; Holliday, Charles W.; Hastings, Jon M. (2011). "The Geographic Distributions of Cicada Killers (Sphecius; Hymenoptera, Crabronidae) in the America" (PDF). The Open Entomology Journal. 5: 31–38. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  7. ^ a b c d e f g h i j k l Holliday, Charles W.; Coelho, Joseph R. (2006). "Improved Key to New World Species of Sphecius (Hymenoptera: Crabronidae" (PDF). Annals of the Entomological Society of America. 99: 793–798.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Nishida, Gordon (December 6, 2004). "Detail of Catalog ID# EMEC55413". Essig Museum of Entomology. Retrieved August 15, 2011.
  9. ^ a b c d Hastings, Jon M.; Schultheis, Patrick J.; Whitson, Maggie; Holliday, Charles W.; Coelho, Joseph R. & Mendell, Angela M. (2008). "DNA barcoding of new world cicada killers (Hymenoptera: Crabronidae)" (PDF). Zootaxa. 1713: 27–38.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Phillips (1999), p. 346
  11. ^ Vander Wall (1990), p. 38
  12. ^ a b c d Coelho, J. R. (1997). "Sexual size dimorphism and flight behavior in cicada killers". Oikos. 79 (2): 371–375. doi:10.2307/3546021. {{cite journal}}: Unknown parameter |month= ignored (help)
  13. ^ a b A. Olson, Carl (2009). "The 17th Annual IECC Conference" (PDF). In Martin, Jeff (ed.). SASI's Communication Quarterly. The 17th Annual IECC Conferenc. SASI. p. 8. Retrieved August 15, 2011. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)
  14. ^ a b c d Coelho, Joseph R. (2007). "Thermoregulation in male western cicada killers (Sphecius grandis Say) in the Chihuahuan desert". Journal of Thermal Biology. 32 (5): 270–275. {{cite journal}}: Unknown parameter |month= ignored (help)
  15. ^ a b Evans (2007), p. 35
  16. ^ Hastings, Jon (1990). "Sexual-size dimorphism in Western cicada killer wasps, Sphecius grandis (Hymenoptera: Sphecidae)". Transactions of the Kentucky Academy of Science. 50 (1–2): 1–5.
  17. ^ a b c Hastings, Jon M. (1989). "The Influence of Size, Age and Residency Status in Territory Defense in Male Western Cicada Killer Wasps (Sphecius grandis, Hymenotera: Sphecidae)". Journal of the Kansas Entomological Society. 62 (3): 363–373. {{cite journal}}: Unknown parameter |month= ignored (help)
  18. ^ a b c Kurczewski, F. E. (1998). "Territoriality and mating behavior of Sphex pensylvanicus L. (Hymenoptera: Sphecidae)". Journal of Hymenoptera Research. 7 (1): 74–83.
  19. ^ a b c d Alcock, John (1975). "The behaviour of western cicada killer males, Sphecius grandis (Sphecidae, Hymenoptera)". Journal of Natural History. 9 (5): 561–566. doi:10.1080/00222937500770431.
  20. ^ a b c d Zolinas, Zachary (1999). "A Dynamic Balance Living in the Sonoran Desert" (PDF). Juntos, Unit Two: 12.
  21. ^ Kosmeier, Dieter (November 16, 2009). "Biology of cicada killer wasps". Lafayette College. Retrieved August 15, 2011.
  22. ^ A. Stange, Lionel (June, 2003). "Cicada killers". Florida Department of Agriculture and Consumer Services. Retrieved August 11, 2011. {{cite web}}: Check date values in: |date= (help)
  23. ^ Charles W. Holliday, Jon M. Hastings & Joseph R. Coelho (2009). "Cicada prey of New World cicada killers, Sphecius spp. (Dahlbom, 1843) (Hymenoptera: Crabronidae)". Entomological News. 120 (1): 1–17. doi:10.3157/021.120.0101.
  24. ^ Coelho, Joseph R.; Holliday, Charles W.; Hastings, Jon M. (2008). "Body Size Relationship Between Sphecius speciosus (Hymenoptera: Crabronidae) and their Prey: Prey Size Determines Wasp Size" (PDF). Florida Entomologist. 91 (4): 657–663. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

Bibliography

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