Plants whose flowers are utilized by adults of Pepsis grossa Fabricius (Hymenoptera: Pompilidae) as a source of nectar

2006·3.3 MB·English

by  Fred Punzo

HYM. RES.
J.
Vol. 15(1), 2006, pp. 171-176
Plants Whose Flowers are Utilized by Adults of Pepsis grossa Fabricius
(Hymenoptera: Pompilidae) as a Source of Nectar
Fred Punzo
Department of Biology, Box 5F, University of Tampa, 401 W. Kennedy Blvd., Tampa, Florida
33606-1490, USA; email: [email protected]
—
Abstract. The spider wasp, Pepsis grossa Fabricius is a common species of wasp found in the
Chihuahuan Desert. This study was conducted in Big Bend Ranch State Park (Brewster Co., Texas)
and reports on flowers of various plant species used by adults of this wasp as a source of nectar.
Althoughnectarwasobtained from theflowers from a totalof19plantspecies,fourofthosespecies
(milkweed: Ascepias texana and A. sperryi; Mexican Buckeye: Ungadia specisosa; Honey Mesquite:
Prosopis glandulosa ) accounted for 73.6% ofall plants utilized. The flowers from these plants were
all characterized by shortcorolla tube lengths (<3.5 mm). At this site, P. grossa exhibited a narrow
trophic niche breadth (Levin's index: B = 0.2816). Other common species of plants whose flowers
were not visited by these wasps are also identified.
Tarantula hawk wasps of the genus information available on the natural histo-
Pepsis (Hymenoptera: Pompilidae: Pepsi- ry of many species (Punzo 2005).
nae: Pepsini) are large, long-legged wasps, These wasps are known to obtain nectar
and are conspicuous components of the from the flowers of a variety of plants
arthropod fauna of desert regions of the (Evans and West-Eberhard 1970, Punzo
southwestern United States and Mexico 2000). However, little information exists
(Punzo 1994a, 2000). The genus Pepsis is on the specific range of plants utilized by
found in North and South America, and any Pepisis wasp (Punzo 2005). In desert
the West Indies, ranging from Utah (lati- regions, where ambient temperatures may
tude 42 N) to Argentina (45 S) (Hurd 1952, exceed 43 C during late spring and sum-
Vardy 2002). Although females of these mer months, female wasps often fly over
wasps typically hunt and paralyze large considerable distances during daylight
spiders as a source of food for their hours, searching for a suitable host (Vardy
carnivorous larvae (Petrunkevitch 1926, 2002, Punzo 2005). Male wasps engage in
Schmidt 2004), the adults are nectivorous energetically costly activities as well, in-
(Williams 1956, Punzo 1994b). cluding an aggressive aerial defense of
Although there have been some studies territories against intruders (Alcock and
on the ecology (Cazier and Mortenson Bailey 1997). Insect flight is energetically
1964, Field 1992, Punzo 2005), territoriality costly under any circumstance. Thus, it is
(Alcock 1979, 2000), hunting behavior essential that adult wasps obtain required
(Petrunkevitch 1926, Cazier and Mortenson nutrients in order to survive and repro-
1964, Punzo and Garman 1989, Punzo duce. In addition, becauseanyspecific type
1994b), neurochemistry (Punzo 1990, of plant tissue or nectar may lack some
1991), venom chemistry (Schmidt 1990, essential dietary requirement, it is only
2004), morphology of venom glands (Scho- through careful selection of particular
eters et al. 1997), and physiology (Punzo plants that an animal can obtain a balanced
1990) of Pepisis wasps, there is a paucity of diet.
172 Journalof Hymenoptera Research
The purpose ofthis study was to identify sotol-lechuguilla plant community. The
the species of plants (flowers) visited by dominant vegetation includes lechuguilla
adults of Pepisis grossa (Fabricius 1798), (Agave lechuguilla), smooth sotol (Dasylirion
formerly described as Pepsis formosa for- leiophyllum), ocotillo (Fouquieria splendens),
mosa (Say), in order to obtain nectar. The mesquites (Prosopis spp.), purple sage
study was conducted in Big Bend Ranch (Leucophyllum frutescens), creosote (Larrea
State Park located in Trans Pecos Texas. divaricata), false agave (Hechtia texensis),
tarbrush (Flourensia cemua), catclaw acacia
DESCRIPTION OF GENERAL
(Acacia berlandieri), prickly pear cacti
STUDY AREA
(Opuutia spp.), yuccas (Yucca spp.), and
Big Bend Ranch State Park (BBRSP, scattered clumps of milkweed (Ascepias
Presidio Co., Texas) lies within the north- spcrryi) and grasses, including chino
ern region of the Chihuahuan Desert. It is gramma (Bouteloua breviseta), fluffgrass
bordered to the west by the Rio Grande (Erioneuron pulchellum), and beargrass (No-
River (RGR), and climatic conditions range lina erumpens). Numerous large rocks and
from semi-arid to arid (Parent 1996, Punzo boulders are scattered along the canyon
2000). Mean monthly air temperatures floor, and the canyon walls are comprised
range from 5.1 C in January to 33.4 C in mainly of sandstone, limestone, and igne-
July, with low and high temperatures of ous rock.
-10.7 and 45.6 C, respectively (U.S. Dept. Pepsis grossa (Fabricius) is the most
of Interior, 2002). Annual rainfall is typi- common Pepsis wasp at this location
cally between 14.6-29.7 cm, depending on (Punzo 2000). Males can be observed in
location and altitude, with 70-80% occur- flight either moving between flowers or
ring from May through October (Medellin- defending territories, feeding at flowers,
Leal 1992). A wide range of topographic or resting on various bushes and plants.
diversity exists within the Park, including Females are readily visible, flying in
igneous rocks, gypsum formations, lime- search of hosts or food plants, or walking
stone deposits that provide a variety of rapidly over the ground surface exploring
substrates including alluvial fans, moutain various crevices and burrows for suitable
ridges, canyons, saline playas, gypsum spiders.
flats, siliceous and gypsum dunes, fine- Twenty square-shaped transects were
textured basins, and freshwater seeps and established within the study site. The
m
springs (Milford 1991), all supporting a di- dimension of each transect was 54 2.
verse plant fauna with distinct vegetative With the aid of several field assistants, I
zones (Powell 1988). walked through each transect in a linear
MATERIALS AND METHODS fashion, following paths delineated by
small yellow cords placed along the
I conducted field studies within the ground in an east-west direction, and
BBRSP in 2003, from late March through separated by a distance of 6 m. Adult
September, when plants ofthis region have wasps were collected using sweep nets.
well developed flowers. The study site was We recorded the following data for each
an area located within a 3.0 km radius of wasp observed and collected: (1) time of
Grassy Banks (29 17'30" N, 103 55'04" W; collection (Central Standard Time, CST);
oeflfevSattaitoen:Ro81a4dm1)70,wh6i.7c6hkismlNocWateodfdLiarjeicttalsy, ((2f)losweexr;)(b3e)iinfgfueteidliinzge,d;t(h4e) tsyppeceioefspolfanptlafnotr
Texas. The western edge of the site is wasps observed resting on vegetation; (5)
bordered by the RGR. The soils along the for flowers at which wasps were observed
canyon floor are a mixture of sand, gravel feeding, flowers were collected and length
and adobe, and support a predominantly of the corolla tube was measured to the
Volume 15, Number 1, 2006 173
Table 1. Species ofplants whose flowers were used as a source ofnectar (percent utilization) by adults of
Pepsisgrossaatastudysite(GrassyBanks)locatedwithinBigBendRanchStatePark,BrewsterCo,Texas,during
2003.Dataexpressedaspercentageutilizationof19foodresources.Datapooledformales(n = 504)andfemales
(n = 488). Scientific and common names of plants based on Powell (1988). B = Levin's measure of trophic
niche breadth.
Plantspecies Meancorollalength(mm)(± SE) Percentutilization
Ascepias texana Torrey (Texas Milkweed) 3.45 (0.41) 28.4
A. sperryi Woods (Sperry Milkweed) 3.55 (0.23) 17.9
Ungadia speciosa Endler (Mexican Buckeye) 2.95 (0.23) 16.1
Prosopisglandulosa Benson (Honey Mesquite) 3.35 (0.28) 11.2
P. pubescens Gray (Screwbean Mesquite) 4.29 (0.18) 3.5
Lycium pallidum Correll (Pale Wolfberry) 5.04 (0.31) T.7
Diospyros texana Scheele (Texas Persimmon) 5.23 (2.45) 3.6
Agave lecluiguilla Torrey (Lechuguilla) 6.02 (2.06) 3.1
Yucca treculeaua Correll (Spanish Dagger) 6.78 (3.03) 3.1
Y. rostrata Engelman (Beaked Yucca) 6.02 (1.87) 0.6
Dasylirion texanum Scheele (Texas Sotol) 5.75 (1.93) 1.8
D. leiophyllum Engelman (DesertCandle) 7.25 (2.11) 0.5
Opuntia imbricata Hawes (Cane Cholla) 7.43 (2.04) 2.7
O. schotti Engelman (DogCholla) 8.02 (2.18) 1.6
O. phaeacantlia Engelman (Purple-fruited Pricklypear) 7.47 (1.99) 0.6
SalviagreggiGray (Autumn Sage) 4.48 (0.32) 1.8
Forestiera angustifolia Torrey (DesertOlive) 8.04 (1.97) 1.1
Nolina erumpens Torrey (Bear grass) 4.88 (0.67) 0.3
Senecio douglasii Benson (Groundsel) 7.79 (1.08) 0.1
= 0.2816
nearest mm using a portable Unitron RESULTS AND DISCUSSION
dissecting microscope fitted with an ocular During daylight hours, male and female
wmeaasspusriwnegregrnido;t(o5)bsseprevcieedstoofvpilsainttsflwowheerrse. wasps were observed resting on shaded
areas of leaves or branches of Cottonwood
Only those wasps that extended their
tongues into the corolla, or that were (Populus fremontii), willows (Salix taxifolia
observed to enter the corolla tube of and S. interior), walnut (Juglaus microcarpa),
flowers with their entire head capsules oak (Quercus oblongifolia), mesquite (Proso-
(and in some cases, part of the thorax as pis pubescens and P. glandulosa), persimmon
milkweed
well) and remain there for at least 20 sec (Diospyros texana), (Ascepias spe-
were considered to be in the act of feeding. ciosa and A. speryii), Mexican buckeye
Each of these wasps was collected, frozen (Ugnadia speciosa), leatherstem (Jatropha
on dry ice, and takenback to the laboratory dioca), and soapberry (Sapiudus saponaria).
to confirm feeding by dissecting the gut These same trees were used as perch sites
and analyzing gut contents. by males during April and May, when
Trophic niche breadth was determined activities associated with territorial defense
using the standarized Levin's index (B) and breeding are most intense (Cazier and
(Levins 1968): B = 1/Y!,Pj> where pj re- Mortenson 1964, Punzo 2000, 2005).
presents the proportion of individuals The species of plants whose flowers
(percent utilization) found on a particular were used as a source of nectar by adults
resource (plant species-flower). Values for of P. grossa are listed in Table 1. This
this measure can range from (narrowest represents the first detailed list of specific
trophic niche: all resources fall under one food plants for a wasp in this genus.
resource category) to 1.0 (resources repre- Because no significant differences were
sented equally in all categories). found between males (n = 504) and
174 Journalof Hymenoptera Research
Table 2. Species of plants common at the Grassy Banks study site in Big Bend Ranch State Park whose
flowerswerenotobserved tobevisited and usedassourcesofnectarbyadultmalesorfemalesofPepsisgrossa
assourcesofnectar.ScientificandcommonnamesofplantsbasedonPowell (1988). Dataoncorolla tubelength
(mm) expressed as means (± SE); N = number ofeach plantspecies.
N
Species
Aloysiagratissima Tronc. (Whitebrush)
Amsonia longiflora Torr. (Bluestar)
Cowania ericifolia Torr. (Heath Cliff Rose)
Croton doicusCav. (Grassland Croton)
Euphorbia antisyphilitica Zucc. (Candelilla)
Fallugia paradoxa Endl. (Apache Plume)
Fouquieria splendens Engelm. (Ocotillo)
Hibiscus coulteri Harv. (Desert Rosemallow)
Justica warnockii Turner (WarnockJustica)
Krameriaglandulosa Torr. (Range Krameria)
Lantana macropoda Torr. (Vinylleaf Lantane)
Mcndora longiflora Gray (Showy Mendora)
Leucophyllum frutescens Berl. (Purple Sage)
Selinocarpus parvifolias Standi. (Little Moonpod)
Senna wislizenii Gray (Senna)
Volume 15, Number 1, 2006 175
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