Sphecius Research Articles

Ring-Billed Gulls Kleptoparasitize Cicada Killer Wasps

Larids are well known for their kleptoparasitic habits, but mostly they steal from conspecifics or other birds. Here we describe Larus delawarensis (Ring-billed Gull) stealing cicadas from Sphecius speciosus (Eastern Cicada Killer) in flight over the Susquehanna River in southern Pennsylvania.

Nesting ecology of the Pacific cicada killer, Sphecius convallis Patton (Hymenoptera, Crabronidae), in the Sonoran Desert

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.

Intra- and Interspecific Prey Theft in Cicada Killers (Hymenoptera: Apoidea: Sphecius).

We studied prey theft in two cicada killer aggregations: Ruby, Arizona (Sphecius convallis Patton) and Easton, Pennsylvania (Sphecius speciosus Drury). Many prey (Tibicen parallelus Davis [Hemiptera: Cicadidae]) were stolen from S. convallis by kingbirds and Greater Roadrunners at Ruby. Seventy percent of kingbird attacks on provisioning wasps were successful. Using sand-filled trap nests baited with a cicada, we tested the hypothesis that conspecific females might kleptoparasitize by laying an egg on the cicada and closing the nest cell. At Ruby, 45% were so appropriated, and at Easton, 52%. Easton data showed that the longer a nest cell was left open, the higher the rate of kleptoparasitism. Hence, intraspecific kleptoparasitism likely occurs at high rates in both populations. Not needing to dig a burrow, or to hunt, capture, and carry a paralyzed cicada favors intraspecific kleptoparasitism in cicada killers. Low cicada availability and intense avian kleptoparasitism of cicada killers may intensify selection pressure for this behavior at the Arizona site. Pirating cicadas may be the only viable reproductive outlet for females that are small or in environments with few prey. We suggest that provisioned nest cell kleptoparasitism may have evolved in cicada killers as an alternative strategy to standard provisioning, given the dual uncertainties of adult body size and prey availability.

English

Abstract Burrowing crayfish are a polyphyletic group of crayfish adapted to life in habitats where surface water is only intermittently available. The burrowing activity of these crayfish creates refugia for numerous other species, making them allogenic ecosystem engineers. While excavating devil crayfish burrows in a roadside ditch in Southern Indiana, USA, a large cicada killer wasp carrying an even larger cicada landed near the authors. The wasp spent a few minutes manipulating its prey, then took flight and flew directly into an unoccupied crayfish burrow in the roadside ditch. The wasp emerged approximately ten minutes later without the cicada and flew away. Female cicada killer wasps typically excavate brooding burrows consisting of numerous cells in which they deposit cicadas for their young to feed on upon hatching. We believe that this particular cicada killer wasp was in the process of provisioning a brooding cell, but used a crayfish burrow instead of digging its own burrow, possibly to save energy. To our knowledge, use of a crayfish burrow by a cicada killer wasp has not been documented before and adds to the list of organisms that benefit from the ecosystem engineering of burrowing crayfish, highlighting the importance of giving these crayfish appropriate conservation attention.

Thermal biology of Pacific cicada killers, Sphecius convallis Patton, in the Upper Sonoran Desert

A comprehensive investigation of the Pacific cicada killer, Sphecius convallis Patton, was undertaken to examine the behavioral and physiological mechanisms by which they are able to complete their life cycle in the thermal extremes of the Upper Sonoran Desert. S. convallis were endothermic, exhibiting elevated and relatively constant thorax temperatures during many activities. Males basked in trees at dawn to warm up, then used a variety of behaviors and perching strategies to maintain thorax temperature during territorial behavior. The thorax temperature of females was highest during provisioning and orientation flights, somewhat lower while investigating burrows, and lowest while digging burrows. The optimal thorax temperature for flight was about 40°C, which was approximated most closely by males resting in the shade during the afternoon. In mating clusters, the mated male was the hottest, the female was coolest and the other males were intermediate. Wasps lost about 5% of body mass during heating treatments, and may use evaporative water loss for cooling. Pacific cicada killers use a complex suite of behavioral and physiological adaptations to regulate body temperature during their nesting season.

Male size and territoriality in the cicada killer wasp Sphecius speciosus (Hymenoptera: Crabronidae)

ABSTRACTMales of the eastern cicada killer wasp, Sphecius speciosus, occupy territories in which they may hover or where they may perch either in trees near one or more emergence holes or on the ground at these spots from which females may emerge. Large males are more likely to hold and defend these territories at a site in northern Virginia. When resident males were captured, held and weighed, the males that replaced them, which were also captured, held and weighed, had significantly lower body weights on average than the residents.

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

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.

Size-Specific Provisioning by Cicada Killers, Sphecius speciosus, (Hymenoptera: Crabronidae) in North Florida

Eastern cicada killer wasps (Sphecius speciosus Drury) mass-provision underground nest burrows with cicadas they capture and paralyze in nearby trees. We studied provisioning by female cicada killers at 2 aggregations in north Florida where a variety of cicada species, with a large range in body size, are used as prey. We captured and measured samples of male and female wasps and we uniquely marked samples of females. We measured and identified paralyzed cicadas that we retrieved from females as they were provisioning their nests. We compared the body sizes of male and female wasps, and cicada prey, between locations. The mean body sizes of male wasps, female wasps, and cicadas from the St. Johns site were much larger than those from the Newberry site. We determined the relationship between the size of individual female wasps and the size of their prey at both locations. Previous studies had concluded that cicada killer hunting is opportunistic, with females provisioning their nests with cicadas of different sex, species, and size in proportion to their relative abundance in the environment. However, we found that individual female cicada killers at these locations exhibited prey specificity by size. Small wasps brought only small cicadas to their nests, as they are likely constrained from carrying large cicadas in flight. Large wasps, not similarly constrained, rarely provisioned with small cicadas. The wasps appear to selectively hunt the largest prey they can carry in flight. Evidence suggests that the cicadas retrieved from wasps at the Newberry site were smaller because small female wasps predominate there, and not because there is a difference in the body size distributions of the cicadas between the 2 local environments.

Cicada Prey of New World Cicada Killers,Spheciusspp. (Dahlbom, 1843) (Hymenoptera: Crabronidae)

As part of a comprehensive study of cicada-killer wasps (Sphecius spp.), we investigated the species and sex of their cicada prey. The 5 New World Sphecius species capture a total of 8 genera (Diceroprocta, Magicicada, Neocicada, Pacarina, Quesada, Tettigades, Tibicen, Uhleroides) and 38 species/subspecies of cicadas in the U.S.A., Cuba and Argentina. S. speciosus, the best-studied species, captures cicadas of 5 genera (Diceroprocta, Magicicada, Neocicada, Quesada, Tibicen,) and 30 species/subspecies, showing no significant overall prey sex bias. At specific sites where more than 50 cicada prey were recorded, the male:female ratio of 6 species brought to nests by Sphecius females varied between 0.524 and 2.259; Chi-square analysis revealed a significant male bias in overall Sphecius spp. prey sex ratios at these sites. The reported significant local variations in prey sex ratios are likely to be due to temporal variations in sex ratios of cicadas available to these opportunistic wasps.

DNA barcoding of new world cicada killers (Hymenoptera: Crabronidae)

We are engaged in a comprehensive study of cicada killers (Sphecius spp.), including their behavioral ecology. At one location, we observed interactions among three putative species of Sphecius, and used DNA barcoding to help clarify relationships among them. For this, we sequenced a fragment of the mitochondrial cytochrome c oxidase subunit I gene. During our study, a new taxonomic key of New World cicada killers, based on morphology, was published, and we expanded the barcoding project to test the congruence between barcodes and this key. In general, barcoding evidence supports morphological distinctions among species; sequence divergences between individuals of different species were within the range expected for congeneric Hymenoptera. However, two conflicts between barcoding and morphological evidence were noted. 1) Haplotypes of Sphecius grandis Say fall into two highly divergent clades, suggesting they are cryptic species. 2) Two clades of S. convallis Patton were found, and the sequences of one clade are virtually identical to those of S. speciosus Drury, suggesting that this clade of S. convallis is conspecific with S. speciosus. Alternative explanations are possible for this result, including hybridization and introgression between the two species. We conclude that our DNA barcoding evidence should be interpreted with caution, but that it has generated interesting questions we hope to resolve with field research coupled with analysis of suitable nuclear gene sequences.

The effect of hind‐tibial spurs on digging rate in female eastern cicada killers

Abstract 1. The function of the large hind‐tibial spurs of female eastern cicada killer wasps (Sphecius speciosus), thought to be adaptations to digging, was examined by measuring the effect of spurs on digging rate.2. Spurs were removed from one group of wasps and left intact in control specimens.3. Wasps with intact spurs removed soil from the burrow at a rate of 0.98 ± 0.11 (16) g dry mass min−1 [mean ± SEM (N)]. Removal of spurs results in an average digging rate just over one‐half that, 0.54 ± 0.13 (9) g min−1.4. The difference in digging rate was primarily because of a twofold greater mass of soil unloaded by intact wasps each time they exited the burrow, rather than the rate at which such loads were delivered.5. Such inefficiency results in an estimated additional 8.2 h requirement to fully excavate an average burrow, or a 1–4% reduction in time available for foraging in spur‐ablated wasps.6. Calculations suggest that the time lost to digging would result in a 3.9–19.5% reduction in foraging success for spurless females.7. These temporal and resulting foraging advantages of hind‐tibial spurs presumably provided selection pressure for their evolution from smaller, pre‐existing setae.

Body size relationship between Sphecius speciosus (Hymenoptera: Crabronidae) and their prey: Prey size determines wasp size

Eastern cicada killers, Sphecius speciosus Drury, are large, ground-nesting, mass-provisioning wasps that use cicadas to feed their offspring. Previous studies have reported that female S. speciosus provide each male offspring with 1 or rarely 2 cicadas, and each female offspring with 2 or rarely 3 cicadas, regardless of cicada size. We collected samples of male and female cicada killers and samples of their cicada prey from 12 locations in 10 different states of the USA. We measured right forewing length of the wasps and dry body mass of the cicadas as indicators of size; ANOVA revealed significant differences in mean masses among local populations of cicadas. We predicted that wasp size would also vary among locations, and would be positively correlated with mean size of local cicada prey. ANOVA did reveal significant differences in mean wing length in both male and female wasps among study sites. Regression analysis, with local mean cicada mass as the independent variable and local mean wasp wing length as the dependent variable, suggests that the size of available cicada prey is a good predictor of size for both male and female S. speciosus.

Sexual Dimorphism of the Femora, Tibiae, and Hind Tibial Spurs in the Eastern Cicada Killer, Sphecius speciosus Drury (Hymenoptera: Crabronidae) in the United States

We examined specific leg structures in eastern cicada killers (Sphecius speciosus) to determine whether they were sexually dimorphic as a result of adaptation or allometry. Females were on average larger than males by every measure, and female hind tibial spurs were longer than those of males, even independent of body mass. The femora of females were not significantly wider relative to femur length than those of males, but the hind tibiae of females were significantly wider than the respective tibiae of males relative to tibia length. Spurs have concave surfaces that contact the loose soil and brush-like structures where spurs meet the substrate; however, these details are essentially the same in males and females. Enlarged hind tibial spurs in females appear to be an exaptation evolved primarily by increase in spur size relative to body size, without changes in shape or external microstructure.

Thermoregulation in male western cicada killers ( Sphecius grandis Say) in the Chihuahuan desert

(1) Male western cicada killers ( Sphecius grandis) had elevated, apparently regulated, thorax temperatures during territorial patrolling. (2) Abdomen temperature increased steeply with increasing ambient temperature, approaching thorax temperature when ambient temperature exceeded 35 °C. (3) Both indirect evidence and heating experiments demonstrated the apparent ability to shunt heat from thorax to abdomen. (4) Dead, dry wasps reached lethal temperatures when placed in full sunlight on the bare ground, and substantially lower temperatures on plants. (5) The percentage of males perching was extremely low, occurring primarily during early morning hours. Most perching occurred on plants, and very little on the ground. (6) In contrast to what has been reported for eastern cicada killers ( Sphecius speciosus), S. grandis males did not appear to use sophisticated behaviors to regulate body temperature during territorial defense, relying primarily on physiological mechanisms. (7) This strategy may be more appropriate for S. grandis in the hotter, drier environment of the lowland Chihuahuan desert.

Behavioral and physiological thermoregulation in male cicada killers ( Sphecius speciosus) during territorial behavior

(1) Male cicada killers had elevated, apparently regulated, thoracic and head temperatures during territorial perching and patrolling in full sunshine. (2) Dead, dry wasps reached near-lethal temperatures on the bare ground, and were hotter with their bodies perpendicular to the sun's rays, as opposed to parallel. (3) The percentage of males perching on the ground, their perch duration, and the percentage oriented perpendicular to the sun decreased during the mid-day. (4) Males used a low-amplitude wing vibration early and late in the day, perhaps boosting heat production. (5) Changes in behavior were related to changes in the intensity of solar radiation.

Effects of Size and Flight Performance on Intermale Mate Competition in the Cicada Killer, Sphecius speciosus Drury (Hymenoptera: Sphecidae)

The characteristics of successfully mating male cicada killers (Sphecius speciosus Drury) were compared to those of unsuccessful males. In the field, successful males were larger and had higher ratios of flight muscle mass to body mass (flight muscle ratios) than unsuccessful males. The elevated flight muscle ratio of successful males was not because of semen transfer to the female nor because of an allometric effect. Better territory-holding ability and flight maneuverability probably contribute to the success of large males with a high flight muscle ratio in nature under most conditions. However, temporal or situational conditions may also exist whereby small males may occasionally have opportunities to mate.

The use of landmarks to define territorial boundaries

Numerous anecdotal reports suggest that members of many territorial species use naturally occurring landmarks to define the boundaries of their territories. In the work reported here, we first tested whether artificial landmarks would be adopted as boundaries by territorial male cicada killer wasps, Sphecius speciosus . To perform this test, we set out wooden dowels on a flat, grassy lawn on which male wasps were defending mating territories. The dowels were situated so that they did not coincide with any existing territorial boundary. After we provided the dowels, the wasps established new territorial boundaries coinciding with the dowels. We hypothesized that using visual landmarks as territorial borders might lower defensive costs, and indeed, focal samples on territorial wasps revealed that borders that were defined by dowels cost less to defend than did borders that were not defined by any landmark. This result suggests that the use of natural landmarks as territorial boundaries may have evolved as a result of the reduced defensive costs that accrue to these boundaries. Furthermore, defensive costs may not depend directly on territory size: territory owners may be able to reduce defensive costs by selecting sites with high tactical defensibility.

An acoustical and physiological analysis of buzzing in cicada killer wasps ( Sphecius speciosus )

Cicada killers (Sphecius speciosus) are large solitary wasps capable of producing a high-amplitude buzzing sound. The buzz was acoustically characterized and its thermal and energetic effects examined. The sound was amplitude modulated, variable in frequency, had many harmonics, and was sometimes interrupted by broad-band buzz pulses. Cicada killer body size was directly related to sound pressure level and inversely related to frequency. Buzzing in males was 70 ± 0.8(21) dB (re 20 μPa measured 3 cm from the dorsum of the thorax) in sound pressure amplitude, with a fundamental frequency of 209 ± 6(20) Hz, while in females buzzes were 72.6 ± 8.3(30) dB and 152.5 ± 5.2(29) Hz. Males, the smaller of the sexes, had buzzes of significantly lower amplitude and higher frequency. Metabolic rate was 0.293 ± 0.024(13) W g−1, or 88% of maximal, during buzzing, and was 5–100 times more costly than file-and-scraper stridulation. Thorax temperature climbed rapidly during sound production and peaked at levels that were nearly optimal for flight. Buzzing may play a role in both interspecific and intraspecific defensive interations.

Sexual Size Dimorphism and Flight Behavior in Cicada Killers, Sphecius speciosus

I examined the size and mass allocation patterns of the two sexes of cicada killers (Sphecius speciosus) in relation to the demands of their flight behavior. Females were nearly 2.5 times the size of males, but there was no difference in the ratio of flight muscle mass to body mass (FMR) between the sexes. Female wasps captured and carried cicadas that were on average 88% heavier than their own body mass, and nearly all were heavier than they should have been able to take off with. Loading of foraging females resulted in a three-fold reduction in FMR as compared to the unloaded state, lower even than the marginal flight muscle ratio for Hymenoptera. Cicadas procured by female cicada killers were not significantly different in body mass or sex ratio from those collected at random. Cicadas had flight muscle ratios that were essentially the same as that of female cicada killers. Females lack sufficient force production to take off with an average cicada, but compensate behaviorally by repeatedly climbing trees and descending under power in the direction of their burrows. Cicada killers of both sexes have relatively high FMRs. Females may have the capacity to capture cicadas in flight. For males high FMR may be important in territorial defense and pursuit of females. Males can be produced at substantial energetic savings to the parent female, and still retain high maneuverability.

NEPOTISM IN A SOLITARY WASP AS REVEALED BY DNA FINGERPRINTING.

Nepotism, the preferential dispensing of benefits to relatives, is common among females of the same generation in the social Hymenoptera (Gamboa et al., 1986; Breed and Bennett, 1987). Although many have speculated that such behavior may have promoted the initial spread of the altruism characteristic of many social insect colonies (Hamilton, 1964; Wilson, 1971; WestEberhard, 1978; Brockmann, 1984), it is not known whether preferential treatment of relatives other than offspring evolved before or after the origin of sociality (Brockmann, 1984; Matthews, 1991). One way to begin to address this issue is to look for such nepotism in a solitary species whose life history and ecology resemble those of the probable precursors of modem eusocial forms. Finding nepotism in such a species would suggest that nepotism possibly preceded, and even promoted, the origin of cooperative insect societies. We investigated the possibility that nepotism toward non-descendant kin occurs in a solitary hymenopteran, the cicada killer wasp (Sphecius speciosus). Sphecius females provision underground nests with paralyzed cicadas upon which they lay their eggs (Dow, 1942; Dambach and Good, 1943; Evans, 1966; Pfennig and Reeve, 1989). We selected this species because, like the probable ancestors of modem eusocial forms (Evans, 1958; West-Eberhard, 1978; Carpenter, 1982; Brockmann, 1984), Sphecius females nest near others and sometimes share the same burrow. When a female enters another's nest, the nest owner exhibits variable tolerance toward the intruder (Dambach and Good, 1943; Pfennig and Reeve, 1989). Field observations and blind experiments have revealed that females nesting 1 m apart [non-neighbors (Pfennig and Reeve 1989)]. In particular, burrow owners were significantly less likely to bite and sting neighbors than non-neighbors when intruders were encountered in the burrow (Pfennig and Reeve, 1989). In addition, females were significantly less likely to seize a neighbor's burrow (Pfennig and Reeve, 1989). Finding evidence of nepotism does not necessarily