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Hilltopping behavior of two species of Astata (Hymenoptera: Crabronidae) in central Arizona
Abstract
Sobre una colina de Arizona central, los machos de la avispa Astata boharti presentan fidelidad hacia determinadas perchas en el suelo, mientras que los machos de Astata occidentalis regresan a perchas en ramitas exteriores de árboles y arbustos. Los machos de ambas especies, así como los de otras especies del género Astata, vuelan desde sus perchas y regresan a las mismas, ocasionalmente en respuesta a insectos en paso. Ambas especies están presentes desde media mañana hasta comienzos de la tarde en el mes de septiembre, cuando las temperaturas aún son altas en el desierto de Sonora. Aunque durante este estudio no se observaron machos de ninguna de las dos especies interactuando con hembras, el comportamiento en que los machos esperan que una hembra pase junto a sus perchas en colinas u otras zonas elevadas es compartido por varias especies de insectos. Este comportamiento “hilltopping” ha sido documentado sólo en pocas avispas de la familia Crabronidae.
... Many butterfl ies, fl ies and ants employ hilltopping mating systems in which males fl y to conspicuous landmarks to await the arrival of receptive females (Skevington 2008). However, only a few wasps have been reported to use this method of mate location (Alcock 1981, Alcock 2007a, Alcock 2007b, Dodson and Yeates 1989. Th e apparent scarcity of hilltopping wasps applies strongly to the Crabronidae, which includes the species that were once placed in the Sphecidae. ...
... Th e apparent scarcity of hilltopping wasps applies strongly to the Crabronidae, which includes the species that were once placed in the Sphecidae. However, hilltopping by a number of crabronids has now been described from a hilltop in central Arizona where males of several species of Tachytes and Astata engage in defense of scattered perching locations where they appear to be waiting for potential mates (Alcock 2007a, Alcock 2007b. ...
... Tachysphex menkei is apparently the fi rst known hilltopping member of the genus with larger males more likely to control lookout perches. Th e behavior of males of this species is very similar to that of another summer-active species of hilltopping crabronid on Usery Peak, Astata boharti F. Parker (Alcock 2007b). Site-faithful males of the two species both defend small landmark territories during the middle of the day at locations near prominent plants growing on the highest parts of the peak. ...
Citation: Alcock J (2011) Hilltopping behavior by males of Tachysphex menkei Pulawski (Hymenoptera, Crabronidae). Abstract Males of the little known crabronid wasp Tachysphex menkei Pulawski engage in hilltopping behavior at the peak of Usery Mountain in central Arizona. Males are active at midday in the late spring at this loca-tion. Individuals perch on and launch out and back fl ights from small rocks near prominent plants grow-ing at the highest parts of the undulating ridgeline that makes up the peak. Th e same set of sites attracted two generations of males (in 2009 and 2010). If site-faithful males are territorial (and if size infl uences territorial success), resident males (those that returned to their perches over at least two days) should be larger on average than the males that replace them after the residents have been removed. Th is expectation was met. In keeping with the hypothesis that hilltopping is a mating system of last resort, only a few males were seen on any given day and no females were observed, suggesting that the population of the species is small and dispersed, at least in central Arizona.
... Of these adults, only 1 was a female, and the majority were trapped in colored pan traps. Finding almost exclusively male A. unicolor adults captured in traps and by net is probably due to the hill-topping behavior of the males (Alcock 2007). The majority of specimens were collected through pan traps (81%) followed by net collection (13%) and captures in vane traps (6%). ...
Native insect predators and parasitoids can help regulate invasive insect pest species. The brown marmorated stink bug, Halymorpha halys (Hemiptera: Pentatomidae), is an introduced pest of fruits and vegetables in the eastern USA that originated in Asia. Surveys for native biological control agents of this pest detected the crabronid predatory wasp Astata unicolor (Hymenoptera: Crabronidae) and the generalist predatory bug Arilus cristatus (Hemiptera: Reduviidae) using the nymphs and adults of this introduced pest as prey. Temporal distribution of the wasp was determined from water pan traps and net collections over 5 years in floral provisioning strips that were established for pollinator conservation programs in tree fruit farms. Blue vane traps used for bee monitoring did not capture A. unicolor in pollinator plantings. Astata unicolor was not found in 6 commercial apple orchards that were monitored concurrently using either pan or blue vane traps over a 4 yr period.
Some male Hemipepsis ustulata defend territories in the crowns of palo verdes Ceridium microphyllum and other trees and bushes located high on the crest of mountain ridges. During May in central Arizona territorial wasps remained at their stations for as many as 5 hr after sunrise; several individuals held the same site for >2 wk. Many palo verdes were never claimed despite the fact that large numbers of wasps visited trees held by other males and would occupy territories from which resident males had been experimentally removed. Territory owners tended to be larger than non-territorial visitors, although some small males in this highly variable species were able to hold certain territories for 2 or more days. Palo verdes that were on or very close to peaktops along a mountain ridge were preferred territories. Prolonged clashes for possession of a tree were observed only at these sites. When resident males were removed from a number of trees along an ascending ridge, higher trees were taken by newcomer males more quickly than lower ones. In generaly, the closer a territory was to a peaktop, the larger the resident male. Smaller wasps either visited many territories as intruders or they established residence in trees below the preferred peaktop sites.-from Authors
Although hilltopping behavior has rarely been reported for crabronid wasps, three species of Tachytes wasps defend hilltop perch sites in central Arizona during the late summer. All three species (T. ermineus, T. spatulatus, and T. sculleni) can be found at the same hilltop during August and September and they perch in many of the same plants at this location. The three species are, however, spatially segregated to some extent in that T. ermineus perches very near the top of large shrubs and small palo verde trees on the hilltop, T. spatulatus perches somewhat lower within many of these same plants, while T. sculleni perches very close to or on the ground about the outer edges of shrubs growing on the hilltop. Males of all three species tend to be site faithful with marked males returning to their perch sites over several days. In experiments in which resident males of T. spatulatus were removed, the replacements that arrived to occupy the trees tended to be smaller, suggesting that large body size confers an advantage in the defense of perching sites in this species. The mating system of these species can be labeled landmark territoriality, with males defending visually conspicuous sites on hilltops that presumably attract receptive females to the territory holders.
Male Grey hairstreak butterflies employed two different tactics, centred on palo verde trees growing on hilltops in central Arizona. During much of the spring flight season of about four months single males repelled all others from a perch tree. Interactions between the territorial resident in a tree and visiting intruder males were frequent but usually brief. One male retained possession of his perch for two weeks, although changes in ownership were generally much more frequent. But territorial behaviour was abandoned during periods when the number of intruders increased sharply, at which time perched males switched to non-aggressive patrolling about the preferred palo verdes. Females occasionally visited the palo verdes and interacted with males but no matings were observed. The mating system of the Grey hairstreak, like that of other similar landmark-defending insects, appears to have evolved in response to a diffusely distributed population of receptive females.
Males of aculeate Hymenoptera differ in the behavioural adaptations employed to locate and secure mates. The ecological and evolutionary bases of these differences are explored in this paper. Male bees and wasps search for females by patrolling widely within emergence-nesting areas or within patches of flowers attractive to conspecific females, or by waiting at landmarks, at specific emergence sites, or at nests. Nest dispersion, flower distribution, the type of female mating system and the nature of male-male competition appear to be key factors in determining the mate-locating behaviour of males. Of special interest in multiple-mating by females, which may be an evolutionary response to the costs of attempting to resist copulation in certain situations. When polyandry occurs, males are under selection pressure to be the last male to copulate with a female prior to oviposition if sperm precedence occurs. In species in which females mate just once, a selective premium is placed on being the first male to reach a virgin female. In either case, because receptive females are a limited resource, there is intense competition among males for access to the resource. The density of competitor males may play an important role in determining whether holding a relatively restricted territory is preferable to the strategy of patrolling widely at various sites which may have females. Territoriality is practiced by males of several species of aculeate Hymenoptera when the number of male competitors is relatively few in number and the distribution of emergence sites or foraging areas of females is clumped in space.
Males of an undescribed species of Cuterebra bot fly defend territories along ridge tops in the Sonoran desert of central Arizona. The most consistently occupied site, an 18 m2 territory at the peak of a ridge, was usually defended by a single male for the entire (2–2.5 h) flight period of the morning. An average of five other males visited the peaktop territory each day from mid-February to early June and engaged in chases with the resident before departing. The resident male was very likely to return the next day but was generally ousted by a successful usurper on this or the third day of his tenure. The behaviour of males of this species of Cuterebra resembles that of several other members of the genus, especially C. latifrons. The landmark-based territoriality of these flies is similar to lek territoriality as defined from mammalian and avian examples.
Males of the lycaenid butterfly Atlides halesus regularly perched in certain portions of particular palo verdes growing on ridgetops in southern Arizona. From their perches, they launched defensive flights that repelled conspecific males from their territories.Different generations of males exhibited consistent territorial preferences. Some tress were almost always occupied during the afternoon over the 4 month spring flight season in 1980, 1981, and 1982; others were less frequently held by territorial males and still others were only very rarely used as a perch site.Perch sites did not contain or attract eclosing, ovipositing, or feeding females which are probably widely and evenly dispersed in the environment as a whole because of the distribution pattern of larval and adult food resources. The mating system of the hairstreak appears to be lek polygyny with males defending landmark perches on prominent topographical features.There are many similarities in the behavior of the hairstreak and the lek-territorial wasp Hemipepsis ustulata. Males of both insects employ the same kind of chase and spiral flights in defense of many of the same palo verdes. Each year they rank the available territorial sites in much the same order as measured by frequency of occupation records. They share many of the same ecological pressures that make it difficult for individual males to monopolize groups of females directly or indirectly.
1.
The breeding season of H. ustulata extends over a 2 1/2 month period in the Sonoran desert near Phoenix, AZ. Individual males are active on mountain ridges for periods averaging about 3 weeks for those wasps captured in the first half of the flight season. Many males live more than 1 month.
2.
Some palo verde trees chosen as landmark territories by male wasps are occupied earlier in the flight season and more consistently thereafter than others. Preferred territories tend to be located higher on ascending ridges.
3.
There is considerable turnover in territory ownership at some trees during the course of the flight season. The average duration of residence by a male wasp was 8 days for all occupants of 18 trees followed over the breeding period. Some changes in ownership occur because an intruder defeats the resident in an aerial contest. Small males are replaced by large ones at preferred territories over the course of the flight season.
4.
Smaller males can adjust their behavior to their social evironment, claiming low-ranking territories if excluded from favored trees or holding prime territories during days when large males are absent. Alternatively, they may abandon territoriality altogether to patrol a series of trees along a ridge.
5.
Despite an abundance of males (>350 marked), females were rarely seen and only two copulations were observed. Male territoriality was not focused directly on emerging or nesting females nor was it focused on food resources attractive to females. The breeding season was prolonged (2 1/2 months) and the operational sex ratio heavily skewed toward males. The wasp's mating system resembles lek polygyny in the sense of Emlen and Oring (1977).
Males of the tachinid fly Leschenaultia adusta perch on small trees and shrubs on the highest parts of Usery Peak in central Arizona. Individuals select twig perches on the downwind side of these plants and fly out spontaneously from time to time or in response to another passing insect. Conspecific males elicit chases that on occasion escalate into elaborate, high-speed pursuit flights that go back and forth near the plant for several minutes. Although several males sometimes perch together briefly in the same plant, typically only one individual remains at a site for more than an hour on any given day. These site-faithful males can be considered territorial residents; they constituted about one-quarter of the males marked during the study. More than half of these residents returned to the same perch plant for two or more days. Perch plants varied in their attractiveness to male flies; male preferences were largely consistent across two years of study. Given that females were occasionally observed mating at male-occupied plants, we place the mating system of L. adusta within the hilltopping territorial category in which males compete for landmark perching sites attractive to receptive females. As is true for other hilltopping insects, receptive females of L. adusta appear to be rare and widely distributed.
During a 2-month spring flight season, male California patch butterflies perch in and defend open areas of 5-10 m2 near prominent palo verdes on ridgetops in the Sonoran Desert. Some males return to defend the same territory several days in a row, each day repelling an average of 3-4 intruders over the 1st 2 hr of the daily flight period. Females fly to ridgetop territories where they are pursued and mated by resident males. Many aspects of the behavior of this species are convergent with other unrelated territorial hilltopping insects. Not all hilltopping butterfly species are territorial and differences in population densities may play a role in the evolution of behavioral diversity within this group. -Author
Male Bembix furcata Erichson (Hymenoptera, Sphecidae) behavior on a hilltop in Queensland
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Ethological studies of digger wasps of the genus Astata (Hymenoptera: Sphecidae)
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Evans, H. E. 1957. Ethological studies of digger wasps of the genus Astata (Hymenoptera: Sphecidae). Journal of the New York Entomological Society 65: 159-185.
Observations on the nesting behavior of Astata occidentalis Cresson in central California
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