Pneumoridae



Moira J. van Staaden *

Bullacris membracioides
Bladder grasshoppers of southern Africa

Containing clade(s): Pneumoroidea; Caelifera; Orthoptera

Table of Contents

Introduction
Characteristics
Natural History
Discussion of phylogenetic relationships
List of included taxa
References


Introduction

 The family Pneumoridae is a group of 17 species distributed along the coast of southern Africa, but also extending northwards into Tanzania and Uganda (map). Most species occur in transitional habitat comprising mosaics of bush and grassland, with the rest in forests or desert. All species are highly cryptic in appearance and behavior, being color matched to their particular food plant and rarely noticed except at night when the loud mate location call of the male may be heard 2 km away. There are large differences in the morphology and behavior of adult males and females. Only adult males are capable of flight and may be attracted to light, but when approached during the day generally do not fly. In several species males can either develop an inflated abdomen or mate as a flightless alternative morph without the anatomy and behavior for sexual signaling (Alexander and van Staaden, 1989). Threatened females and nymphs will drop to the ground and feign death (thanatosis), although nymphs may also jump. The family is significant because individuals possess two forms of ears, providing the first functional evidence for the evolutionary transition from stretch to hearing organs in insects (van Staaden & Römer 1998).

Members of the Pneumoridae may be locally abundant, with several species often occupying the same locality. However, there is reason to believe that many populations are threatened or recently extinct.

You can see pictures of several species in the list of included taxa, as well as alternative males, and typical habitats.

The species can be distinguished by external characteristics detailed in the most recent revision of this group by Dirsh (1965; Key to genera and species), although there is now some doubt as to the authenticity of several taxa (see "Discussion of phylogenetic relationships").


Characteristics of Pneumoridae

Natural History

 The almost complete absence of field observations and knowledge of pneumorid behavior cited by Dirsh (1965) is largely a function of their patchy spatial and temporal distribution, probably in turn correlated with the availability of the appropriate food plants. This is particularly true for females, nymphs and alternative males which do not fly. The following natural history account is based mainly on extensive observation of Bullacris membracioides and Pneumora inanis in KwaZulu-Natal, and B. unicolor in Namaqualand, and less detailed observations of six other species.

Bladder grasshoppers are associated with relatively few food plants, an average of two food plants per species. These are mostly members of the Asteraceae, but also include representatives of Aizoaceae, Zygophyllacae, Rosaceae, Anacardiacae, and Lamiaceae. Food plants are important for the maintenance of crypsis by matching coloration, although exceptions occur in the occasional yellow-brown , B. membracioides,and in B. discolor,which has bright red, wings, legs and pronotum. Crypsis is further enhanced by fecal dispersal and inconspicuous eating patterns; e.g. for large leafed plants, animals eat only from the edges of the leaf in such a way that they minimize any change in its outline.

Nymphs and adult females are primarily diurnal in their activities, feeding in bursts during the day and sleeping at night. Oviposition occurs directly under the food plant in the common acridoid manner, with egg laid in pods 3-5 cm beneath the soil surface. Development time and relevant environmental signals are unknown but egg hatching appears to coincide with rains and the availability of ephemeral food resources. There are 4-6 instars, with males expanding at the final moult to attain the inflated form. These males are active at night, with different species stridulating at different times.

Adult males stridulate with leg and abdominal files to produce intense, species-specific mate location calls amplified by the abdominal resonator. Females respond with wing-abdominal or elytro-leg stridulation, producing a softer, less specific call which enables males to locate them by duetting. No complex courtship behavior has been observed. B. membracioides call at times when nocturnal, downward refracting temperature inversions create a tunnel effect with sound caught between the ground and zones of different temperatures, resulting in extremely large sound transmission distances of up to 2 km for the male signal (van Staaden & Römer 1997). This signal range is achieved by adaptations in the signal, behavior and sensory system of the animal which has the most sensitive hearing yet recorded for an insect (van Staaden & Römer 1998).

In captivity adult males are agonistic towards one another and will fight to the death, but females and nymphs tolerate higher densities. Male aggression does not extend to the alternative male morph in B. membracioides, suggesting that these are not recognized as rivals even though they remain in copula for extended periods of time. Proximate and ultimate causes for alternative male morphs are presently unknown.


Discussion of phylogenetic relationships

 No fossil evidence has yet been found to establish affinities of the family. Comparative morphological studies based largely on genital characteristics (Dirsh 1965) and wing venation (Smart 1953; Ragge 1955) suggest that pneumorids are a primitive family derived from general Caeliferan stock even earlier than Locustopsidae and earlier than other living Caeliferan superfamilies (Ragge 1955). Rehn (1941) considered them an ancient group equivalent to the Tetrigoidea. Pneumorids resemble Acridoids in many respects and are clearly related to these, but the exact nature of the relationship is uncertain. They may be primitive Orthoptera which developed in parallel with the Acridoidea and share characters by convergence, or highly specialized Acridids which have become secondarily simplified (Dirsh 1965). There have been no morphology-based cladistic tests of these hypotheses. Molecular data of Flook and Rowell (1997) suggest that the Pneumoridae branch off after the Eumastacoidea, but before the Acridoidea.

Alexander and van Staaden (1989) suggested that north eastern forest species are basal and south western desert species derived, but no phylogeny has yet been derived for the family. A molecular phylogeny is under construction. In the most recent systematic revision, Dirsh (1965) recognized 9 genera containing 17 species. However several genera and species are known from only one sex or a single individual and are of dubious status. Genera with non-inflated males are particularly troublesome. Dirsh considered them "parallel to the species with inflated bodies", placing them in separate genera (Pneumoracris, Paraphysemacris, Parabullacris) and largely discounting van Son's view (in litt.) that these were neotenic forms. Present data suggest that neither view is correct. A non-inflated male morph occurs alongside the inflated male in at least two species. Mating behavior, food plant specificity and morphological measurements clearly indicate that these are alternative morphs rather than simply neotenic forms (Alexander and van Staaden 1989). Consideration of food plants and geographic distribution suggests that the non-inflated genera may be alternative males of inflated species (i.e. Pneumoracris browni = Perinqueyacris namaqua; Paraphysemacris spinosus = Physemacris variolosus). However, the situation of Parabullacris vansoni with respect to the B. unicolor complex is less clear.


List of included taxa

References

 Alexander AJ, van Staaden MJ (1989) Alternative sexual tactics in male bladder grasshoppers (Orthoptera, Pneumoridae). In: Bruton, M.N. (ed), Alternative Life-History Styles of Animals. pp 261-277. Kluwer Academic Publishers, Dordrecht.

Alexander AJ (1992) The bladder grasshopper. a "nu-nu" of mystery and intrigue. African Wildlife 46: 261-262

Dirsh VM (1963) Three new genera and species of the family Pneumoridae (Orth. Acridiodea). Eos 39: 177-184

Dirsh VM (1965) Revision of the Family Pneumoridae (Orthoptera: Acridoidea). Bulletin of the British Museum (Natural History) (Entomology) 15: 325-396

Ewer DW (1964) Notes on acridid anatomy, VI. On the pterothoracic musculature of Bullacris (Roberts) and Pneumora (Stål) (Orthoptera: Pneumoridae). Journal of the Entomological Society of Southern Africa 26: 411-424

Flook PK, Rowell CHF (1997) The phylogeny of the Caelifera (Insecta, Orthoptera) as deduced from mtrRNA gene sequences. Molecular Phylogenetics and Evolution 8: 89-103

Lewis RT (1891) On the stridulating organs of Cystocaelia immaculata. Quekett Microscopical Club Journal 4: 243-245

Péringuey L (1916) Descriptions of new and little-known Orthoptera in the collection of the South African Museum, Part 1. South African Museum Annals 15: 401-413

Ragge DR (1963) The nymphal wing-pad tracheation and adult axillary sclerites of the Pneumoridae (Orthoptera: Acridoidea). Trans. American Entomological Society 13: 85-191

Ragge DR (1955) The wing-venation of the Orthoptera Saltatoria, with notes of dictyopteran wing-venation. London, British Museum (Nat. Hist.) 159 pp.

Rehn JAG (1941) On new and previously-known species of Pneumoridae (Orthoptera: Acridoidea). Trans. American Entomological Society 67: 137-159

Smart J (1953) On the wing-venation of Physemacris variolosa (Linn.) (Insecta: Pneumoridae). Journal of Zoology (London) 123: 199-202

Thunberg CP (1775) Pneumora, et nytt genus ibland insecterne, uptåckt och beskrifvit. K. svenska Vetenskapakad. Handl. 36: 254-260

van Son G (1955) A Locust Mystery. Bulletin van die Transvaal Museum, November 1955: 7

van Son G (1958) Locust Mystery Solved. African Wildlife 12: 26-28

van Staaden MJ, Römer H (1997) Sexual signalling in bladder grasshoppers: tactical design for maximizing calling range. J. Exp. Biol. 200: 2597-2608

van Staaden MJ, Römer H (1998) Evolutionary transition from stretch to hearing organs in ancient grasshoppers. Nature 394: 773-776


Here you can find news and updates of ongoing pneumorid projects.


About this page

 Moira J. van Staaden
E-mail: mvs@caspar.bgsu.edu
Dept of Biological Sciences
Bowling Green State University, Bowling Green, OH 43403, USA

Last modified 22 December 1998

Copyright © 1997 Moira J. van Staaden
All rights reserved.



Title Illustration

Bullacris membracioides, adult male, KwaZulu-Natal, South Africa
Photograph copyright © 1995, B-A. Gereben-Krenn.

All Other Photographs

Copyright © 1997, M.J van Staaden & R.Huber