NESTING BEHAVIOR OF LARROPSIS CHILOPSIDIS AND L. VEGETA (HYMENOPTERA: SPHECIDAE: LARRINAE)

In their revision of the genus Larropsis, Bohart and Bohart (I966) reported prey records or only two of the 25 described species. L. divisa (Patton) had been observed preying on immature camel crickets, Ceuthophilus sp., by Williams (93), who also presented notes on nesting behavior; and R. M. Bohart himself had taken L. filicornis Rohwer with an adult camel cricket of the genus A mmobaenetes. A detailed study of the nesting behavio.r of A ncistromma distincta (Smith), a member o.f a closely related genus (often ranked as a subgenus of Larrosis), was published by Evans. (958a). The present paper adds to the limited knowledge Larropsis biology by reporting observations on the nesting behavior of L. chilopsidis (Cockerell and Fox) and L. vegeta (Fox). These two species are very similar structurally, live in sand dune habitats,. and exhibit virtually identical nesting behavior.

Mexico. At this locality, females were commonly observed in the dunes during the morning and again during late aftern.oon; during the heat of midday they were rarely seen. Their activity consisted mainly of walking in sinuous patterns over the sand and investigating small depressions and burrow entrances in the sand surface. In contrast to so.me Larrinae, females did not flicker their wings while hunting. Often they dug with the front legs and occasionally they entered holes in the sand. Most females were followed by one or more satellite flies hovering 6-8 cm behind (Table I). We captured several of these flies and found that two species were involved: Senotainia rutqventris Coquillett and S. (?) flavicornis (Townsend) (Sarcophagidae, Miltogramminae) (det. R. J. Gagn) (Table   ). L. chilopsidis females appeared to spend a great deal of time searching, as evidenced by the many hours we spent following them before one was observed to locate her prey. All L. chilopsidis observed preyed on z/mmobaenetes phrixocnemoides (Caudell) (Gryllacrididae, Rhaphidophorinae), a sand treader camel cricket (4 records). We recovered the cricket and threw it at the wasp, which seized it and held on while the prey still jumped around. The wasp stung the prey several times, preventing further movement. Ater a short period the wasp grasped the antennae o the cricket and started to pull it. However, the cricket was twice the length o the wasp and doubtless weighed several times as much, and ater a ew seconds she stopped trying to move it and began to feed at the ventral side o the neck region. Ater 3o seconds she abandoned the prey and resumed her searching behavior. She did not return to the cricket, which after one hour was collected for identification. At o942 the wasp was observed to reappear at the mouth o the burrow, digging at th, e sides o. the hole. As she moved toward the surface she turned, and sand rom the burrow gradually filled the burrow behind her. At o943 she flew away, leaving the top cm o the burrow unfilled. She made no attempt to use sand rom the dune surface to fill the hole. The burrow was evidently that o. a cricket, possibly the one she had captur.ed. It was dug into a. slope o about 2o degrees and was steep for the first 5 cm (about 3o-35 degrees with the surface) the first cm was filled with sand and the next 4 cm was open. Beyond this the burrow had been filled and was impossible to trace. The cell with the paralyzed cricket was located 28 cm bel.ow the sand surface and 4o cm from the burrow entrance. The prey was positioned on its back and bore the Larropsis egg as well as a small satellite fly larva ( Fig. ).
Observation C.--At 735 on 28 June a wasp was seen entering a burrow. About .5 min later she emerged 5 cm ro.m the burrow mouth and immediately dug herself back in. Both times she entered the ground she had to dig for 5-2o seconds in order to get through the loose surface sand. At x95 the wasp had not emerged from the burrow. At o830 on the following day we excavated the area around the filled burrow and found a female camel cricket 9 cm deep and 35 cm from the burrow mouth. An egg was present on the cricket, which had completely recovered rom paralysis. Observation D.--At o9oo on 3o June a Larropsis chil,opsidis female, followed by a satellite fly, was observed digging for about 3o seconds before entering a burrow. The fly perched on a small twig, about 3 cm from the burrow mouth, as the wasp entered. The fly then flew to the burrow mouth but soon returned to her perch; she continued to show interest in the hole and several times moved between it and various perches. This alternated with bouts of flying in o.5 m circles around the burrow. At one point the perched fly oriented to a passing harvester ant, Pogon,omyrmex sp., which was about the same size and color as female L. chilopsidis. At o912 the fly was still present but seemed t.o show less interest in the burrow, and by o93o it had left the area. At iooo the wasp had not emerged from the burrow so the mouth was covered with an insect net. Upon returning to the area at 14oo we found the dead wasp in the net, evidently a victim of the intense afternoon heat. The nest, which was located on level ground about o.5 rn from a large shrub, was excavated that afternoon, but the filled burrow was impossible to trace. Cell and prey were locat.ed 31 cm from the burrow entrance. The female camel cricket prey, which had an egg attached, was apparently just recovering from paralysis, as it was able to walk slowly.
Egg and Larva.--The egg of L. chiloDsidis is 2.o-2.2 mm long and about o.4 mm wide (N--3). It is laid transversely between the front and middle coxae of the prey, with one end pr.essed against one of the front coxal cavities (Fig. ), This is exactly the same egg position described for dncistromma distincta (Evans,I958a). In two observations (C and D) the prey seemed to recover from paralysis about 6-8 hours after being stung. The egg from observation C hatched in 44 hours, which is comparable to the 2 days reported for d. distincta by Evans. The larva, however, died soon after hatching. The egg from interaction B failed to hatch. As mentioned above, a satellite fly had been observed landing on the prey in this instance. In the cell a single fly larva was observed immediately behind the wasp egg; it was mm in length and positioned at one end ,.?f the egg, between it and the right m.;ddle coxa of the prey (Fig. ). By 6.5 hrs after the egg was laid it had been completely consumed by the fly larva. Sixteen hours later the larva had entered the body of the cricket, which was dead. By the morning of 4 July (6 days after the egg had been laid) the maggot pupated, leaving only the legs, head, and end of the cricket abdomen unconsumed. The pupa.rium was brick red in color .and measured 2 X 5 mm. Psyche September-Deeember OBSERVATIONS ON L. YEGETA Females of this species are about the same size as those of L. chil, opsidis (approximately 15 ram) but are much darker in color, almost black. Bohart and Bohart (1966) reported the species from the central Great Plains in Wyoming, Colorado, western Nebraska, northern Arizona., and the base of the Texas panhandle. Our observations were made near Hasty, in southeastern Colorado, in early July 1975.
The behavior of this species appears almost identical to that of L. chilopsidis. Although o.ne female L. vegeta was i.ollowed by a satellite fly (not identified), the majority were not (Table ). Only one interaction between wasp and prey was observed. At IOOO on 5 July, a female was observed digging on the surface of a dune.
She located a burrow and entered. We excavated the burrow about 5 minutes later; as it had not been filled it was easy to. trace to the cell. The burrow fo.rmed an angle of about IO degrees with the flat sand surface. It was straight for 34 cm, where the wasp and paralyzed prey were found about 15 cm below the surface. The prey was an immature female sand treader camel cricket, Daihiniella sp. The wasp had not yet laid an egg on her prey. DISCUSSION Both Larropsis chilopsidis and L. vegeta fema.les obtain their prey by searching the sand sur(ace or sand treader camel cricket burrows.
Apparently they use olfactory cues to locate activ.e burrows. Support (or this hypothesis comes rom an observation made ater removing a cricket prey and egg o L. chilopsidis rom the cell. A searching emale walk.ed into the hole we had dug out and showed much interest in the empty cell, digging in the area for several seconds. Very little is known about the biology o sand treader camel crickets. There are several genera in the group (Tinkham, I942), all characterized by a "sand basket" o spurs on the upper distal end o the posterior tibiae. An dnmobaenetes phrixocnemoides kept in the laboratory was observed to remo.ve sand rom its burrow by moving backwards, pushing sand behind it with the aid o the sand baskets. These insects are nocturnal and dig a simple, oblique burrow in which they pass the day (Tinkham,942). A searching emale Larropsis is therefore more likely to. ind her prey deep in the burrow.
Our observations suggest that both species normally /]nd and sting their prey underground, where the cricket has little opportunity to escape. In observation A (L. chilopsidis) the wasp had evidently encountered a cricket near the sand surface, where it was able to. escape by leaping away from the wasp. Even though searching LarroDsis females are usually followed by satellite flies, they normally successfully avoid these parasites by capturing their prey underground. 8enotainia species will not enter burrows and will larviposit only on exposed prey outside the burrow (Evans and West Eberhard,97o,p. 6 ). This was revealed when a. satellite fly was observed to follow a L. chilosidis female as she entered a camel cricket burrow. Although the fly appeared to show much interest in the burrow mouth she did not enter but perched nearby for about 2o minutes (observation D). A satellite fly was successful in larvipositing on the prey in the single observation (B) where the female had stung the prey outside the burrow. In this case the cricket had presumably escaped from the wasp and had been chased, subdued, and eventually dragged back to its burrow.
Both of the species studied do not dig their own nests but utilize burrows of their prey, thus conserving the energy required to dig a nest. Use of pre-existing cavities for nesting is common in the subfamily (Larrinae) to which LarroDsis belongs, having been reported in such genera as Liris (Steiner,962), Lyroda (Evans,964), dncistromma (Evans,I958a), and Larra (Williams,I93,928;Smith,935). A ncistromma distincta females do some digging, but usually take advantage of natural cavities in the rocky soil of their nesting habitat. Species of Larra evidently locate their mole cricket prey in their burrows using olfactory cues, then attack the prey and lay their egg in the host's burrow, much in the manner of Larropsis species. However, the position in which the egg is laid is quite different in the two genera, Larra spp. laying the egg just back of the base of a hind leg, Larropsis spp. between the front and middle legs. These different egg positions are undoubtedly adaptive and are related to the fact that mole crickets dig with their front legs, sand treader camel crickets with their hind legs. Mole crickets attacked by Larra recoved quickly from paralysis and resume normal activities until killed by the developing wasp larv.a; thus. it is to the advantage of the wasp larva that it be coiled posteriorly and no.t in a position to interfere with digging by the host. Sand treader camel crickets attacked by Larropsis spp. also recover from paralysis within a few hours and appear to be abl.e to resume normal activities. One cricket, which we dug up some 5 hours after it was stung (observation C, L. chilopsidis), leaped from the excavated cell, and it was only when we captured the insect and found the wasp's egg that we were able to be sure it was the prey. However, we have no. actual evidence that the crickets are able to dig their way out of the cells into which they are packed by the wasps.

Psyche [September-Deeember
These traits (temporary paralysis and use of the host's burrow as a nest) are often regarded as primitive, since they resemble the condition in structurally generalized wasps such as Scolioidea (Evans,958a,b). However, they might equally well be derived traits, suited to the ecology of their prey, and likely to reduce the success, of satellite flies. LITERATURE CITED BOHART, G. E., AND R. M. BOHART