Zoraptera Silvestri 1913

Introduction

The order Zoraptera is one of the least diverse and most poorly understood of insect lineages. Zoraptera are minute, hemimetabolous insects superficially resembling barklice (Psocoptera) or termites (Isoptera). Individuals are generally less than 3 mm in total body length, exclusive of their antennae, and are gregarious. Overall, zorapterans are quite homogenous in their morphology and tend to be off-white (mostly nymphs) to brown in color. Individuals of each species occur in two morphs: eyed and winged forms that then shed their wings after dispersal or blind and apterous forms that predominate in colonies. The order consists of a single family, Zorotypidae, presently with two recognized genera. Only one, very preliminary attempt has been made to elucidate phylogenetic relationships among zorapteran species (Engel, 2003b). A complete monograph of the order has been in preparation for many years and should be finished in the next 3-4 years (Engel, unpubl.)

Zorapterans live in small colonies of 15-120 individuals which they found in the crevices or under dead bark of moist, decaying logs (they will also colonize man-made sawdust piles). Species feed principally on fungal hyphae and spores but can also be general scavengers or predators, victimizing nematodes, mites, or other tiny arthropods. Other aspects of their biology and behavior are considered by Choe (1994a, 1994b, 1995, 1997), Engel (2003a), and Valentine (1986).

Although considered rare by many entomologists, once a successful "search-image" is developed for locating zorapteran habitats, then species are typically not difficult to locate. In fact, the "rarity" of zorapterans may be merely apparent and more a result of poor collecting than any actual scarcity. Certainly some species are uncommon, but overall the actual abundance of the order likely does not live up to its reputation for scant occurrence (this is particularly true for the North American species, Zorotypus hubbardi: Engel, pers. obs.). Wilson (1959) went so far as to identify a "Zoraptera stage" in decomposition whereby logs can be easily torn with an ordinary collecting tool. Naturally-formed spaces in logs not reached by light harbor zorapteran colonies. Once the wood is disturbed individuals will quickly scatter to avoid detection, thus fogging with a general insecticide prior to dissecting a log can aid collection. Individuals are best preserved in ethanol.

Zorapterans are principally distributed pantropically with only four species occurring North of the Tropic of Cancer (i.e., North of 23.5°N): Z. hubbardi in the United States, Z. snyderi in Florida, and Z. sinensis and Z. medoensis in Tibet. Almost all of the northernmost records for Zorotypus in North America are from sawdust piles rather than natural logs suggesting that the distribution in regions with considerable winter frosts is artificially influenced by human activity (Engel, 2003a, 2004). The effects of global climate change on northern migrations of Zorotypus are uncertain but are likely to permit species to expand their distributions significantly in North America and Asia. Aside from the aforementioned four species, all zorapterans are tropical. Even those fossil records of Zoraptera are all from ambers formed in warm-tropical paleoclimates (Engel and Grimaldi, 2002). While species have at times been considered highly endemic and hypothesized to have poor dispersal abilities, increasingly individual species are being discovered to have larger geographic ranges than previously understood (e.g., New, 2000; Engel, 2001). Such species provide evidence of some degree of dispersal ability in zorapterans so as to maintain specific integrity over these ranges. Furthermore, the presence of zorapterans on distantly isolated islands of relatively recent geological age such as Hawaii indicates some dispersal capabilities.

Characteristics

The order can be characterized as follows (from Engel, 2003a, 2004): adults minute (around 3 mm), hemimetabolous Neoptera; mouthparts mandibulate; lacinia fused to stipes, lacinia with strong inner, apical tooth; maxillary palpus five-segmented; labial palpus three-segmented; distal palpal segment of labial and maxillary palpi larger than preceding palpal segments; prementum divided; antennae nine-segmented (except in Octozoros where it is eight-segmented), moniliform; compound eyes and ocelli present in winged forms; lateropleurite and laterosternite differentiated in alates; wings membranous with reduced venation or wings frequently absent, forewings narrow and paddle-shaped owing to reduced anal lobe, forewing with radial, median, and cubital veins fused at base; hind wings smaller than forewings; all wings dehiscent, shed by indefinite basal fracture; coxae large; metafemora stoutly expanded, with stiff spines along ventral surface, metatibial depressors greatly developed (as contrasted with the greatly developed metatibial levators of saltatorial lineages such as Orthoptera); tarsi two-segmented, first segment minute, second segment elongate; claws simple; abdomen 11-segmented; two abdominal ganglia; cerci present, short, unsegmented (except in Z. goeleti a weak, distal second segment is evident); ovipositor absent; male genitalia asymmetrical, gonostylus absent; female with 4-6 panoistic ovarioles; six Malpighian tubules; gregarious.

• reduced wing venation, in paddle-shaped wings that are shed at basal fractures.
• gregarious lifestyle, with individuals living in colonies up to about 120 individuals.
• polymorphism in populations; with blind, apterous individuals dominating during colony life, but populations produce eyed alates (individuals with wings) for dispersal and founding new colonies.
• two-segmented (dimerous) tarsi.
• enlarged metafemora (hind femurs), with rows of distinctive spines along ventral surfaces.
• males with a distinctive "mating hook" and unique mating behaviors.
• unique grooming behaviors (Valentine, 1986).

Phylogenetic Position of Zoraptera

Although there are numerous hypotheses concerning the phylogenetic placement of Zoraptera (e.g., Hennig, 1981; Boudreaux, 1979; Rasnitsyn, 1998; Wheeler et al., 2001), a conclusive placement of the order remains controversial and elusive. At present the most well-supported position recognizes the Zoraptera as polyneopterous insects (admittedly with numerous reductions in structures from the typical polyneopteran groundplan: Grimaldi and Engel, 2005) and as sister to the webspinners [order Embiodea (= Embioptera, or Embiidina)] (Engel & Grimaldi, 2000; Grimaldi & Engel, 2005). This conclusion is based on numerous shared apomorphic traits the most notable being the unique hyper-development of the metatibial depressors in both orders, dehiscent wings, reduced anal region of wings (i.e., narrow, paddle-shaped wings), gregarious behavior, and apterous morphs (occurs among some male Embiodea). Additional shared traits are discussed by Engel and Grimaldi (2000).

Fossil History

The order is clearly ancient, perhaps diverging from the Embiodea during the Late Triassic or Early Jurassic. Relatively modern-looking species of both orders are known from middle Cretaceous amber (Engel and Grimaldi, 2002; Grimaldi et al., 2002). Indeed, Cretaceous zorapterans already exhibit the development of dual morphs (eyed alates versus blind, apterous individuals) within the species. Thus, typical zorapterans (even belonging to the moder genus Zorotypus) were already established by the middle Cretaceous (about 100 million years ago). Unfortunately, earlier records of Zoraptera will be challenging to find since these minute, delicate insects require remarkable fidelity in preservation to allow meaningful identification, something best achieved in amber. Presently, however, insect-bearing ambers are known only back as far as the earliest Cretaceous and it may be decades before Late Triassic or Jurassic zorapterans are recognized.

Other Names for Zoraptera Silvestri 1913

• zorapteron
• Floridazoros
• Usazoros
• Meridozoros
• Brazilozoros
• Centrozoros
• Latinozoros
• Formosozoros
• Zorotypidae
• Vernacular Names: Zorapterans

References

Boudreaux, H. B. 1979. Arthropod phylogeny, with special reference to insects. Wiley Interscience; New York, NY.

Caudell, A.N. 1920. Zoraptera not an apterous order. Proceedings of the Entomological Society of Washington 22: 84-97.

Chao, R. F., and C. S. Chen. 2000. Formosozoros newi, a new genus and species of Zoraptera (Insecta) from Taiwan. Pan-Pacific Entomologist 76(1): 24-27.

Choe, J. C. 1989. Zorotypus gurneyi, new species, from Panama and redescription of Zorotypus barberi Gurney (Zoraptera, Zorotypidae). Annals of the Entomological Society of America 82(2): 149-155.

Choe, J. C. 1994a. Sexual selection and mating system in Zorotypus gurneyi Choe (Insecta: Zoraptera). I. Dominance hierarchy and mating success. Behavioral Ecology and Sociobiology 34: 87-93.

Choe, J. C. 1994b. Sexual selection and mating system in Zorotypus gurneyi Choe (Insecta: Zoraptera). II. Determinants and dynamics of dominance. Behavioral Ecology and Sociobiology 34: 233-237.

Choe, J. C. 1995. Courtship feeding and repeated mating in Zorotypus baberi (Insecta: Zoraptera). Animal Behaviour 49: 1511-1520.

Choe, J. C. 1997. The evolution of mating systems in the Zoraptera: Mating variations and sexual conflicts. Pp. 130-145. In Choe, J. C., and B. J. Crespi (eds.), The evolution of mating systems in insects and arachnids. Cambridge University Press; Cambridge, UK.

Crampton, G.C. 1920. Some anatomical details of the remarkable winged Zorapteron, Zorotypus hubbardi Caudell with notes on its relationships. Proceedings of the Entomological Society of Washington 22: 98-106.

Crampton, G.C. 1922. Evidences of relationship indicated by the venation of the forewings of certain insects with special reference to the Hemiptera-Homoptera. Psyche 29: 23-41.

Engel, M. S. 2000. A new Zorotypus from Peru, with notes on related neotropical species (Zoraptera: Zorotypidae). Journal of the Kansas Entomological Society 73(1): 11-20.

Engel, M. S. 2001. New Neotropical records for three Zorotypus species (Zoraptera: Zorotypidae). Entomological News 112(4): 278-280.

Engel, M. S. 2003a. Zoraptera. Pp. 1201-1203. In Resh, V. H., and R. T. Carde (eds.), Encyclopedia of insects. Academic Press; San Diego, CA.

Engel, M. S. 2003b. Phylogeny of the Zoraptera. Entomologische Abhandlungen 61(2): 147-148.

Engel, M. S. 2004. Zoraptera. Pp. 637-640. In Llorente-Bousquets, J. E., J. J. Morrone, O. Yanez-Ordonez, and I. Vargas-Fernandez (eds.), Biodiversidad, taxonomia y biogeografia de artropodos de Mexico: Hacia una sintesis de su conocimiento [Vol. IV]. UNAM; Mexico D.F., Mexico.

Engel, M. S., and D. A. Grimaldi. 2000. A winged Zorotypus in Miocene amber from the Dominican Republic (Zoraptera: Zorotypidae), with discussion on relationships of and within the order. Acta Geologica Hispanica 35(1): 149-164.

Engel, M. S., and D. A. Grimaldi. 2002. The first Mesozoic Zoraptera (Insecta). American Museum Novitates 3362: 1-20.

Grimaldi, D., and M. S. Engel. 2005. Evolution of the insects. Cambridge University Press; Cambridge, UK.

Grimaldi, D. A., M. S. Engel, and P. C. Nascimbene. 2002. Fossiliferous Cretaceous amber from Myanmar (Burma): Its rediscovery, biotic diversity, and paleontological significance. American Museum Novitates 3361: 1-72.

Gurney, A.B. 1938. A synopsis of the order Zoraptera with notes on the biology of Zorotypus hubbardi Caudell. Proceedings of the Entomological Society of Washington 40: 57-87.

Kukalova-Peck, J., and S.B. Peck. 1993. Zoraptera wing structures: Evidence for new genera and relationship with the blattoid orders (Insecta: Blattoneoptera). Systematic Entomology 18: 333-350.

Kuznetsova, V. G., S. Nokkala, and D. E. Shcherbakov. 2002. Karyotype, reproductive organs, and pattern of gametogenesis in Zorotypus hubbardi Caudell (Insecta: Zoraptera, Zorotypidae), with discussion on relationships of the order. Canadian Journal of Zoology 80(6): 1047-1054.

New, T. R. 1978. Notes on Neotropical Zoraptera, with descriptions of two new species. Systematic Entomology 3(4):361-370.

New, T. R. 2000. Zoraptera (Insecta) in East Malaysia: Notes on Zorotypus caudelli Karny. Oriental Insects 34: 77-82.

Poinar, G. O. 1988. Zorotypus palaeus, new species, a fossil Zoraptera (Insecta) in Dominican amber. Journal of the New York Entomological Society 96(3):253-259.

Rasnitsyn, A. P. 1998. On the taxonomic position of the insect order Zorotypida = Zoraptera. Zoologischer Anzeiger 237(2-3): 185-194.

Wheeler, W. C., M. Whiting, Q. D. Wheeler, and J. M. Carpenter. 2001. The phylogeny of the extant hexapod orders. Cladistics 17: 113-169, 403-404.

Wilson, E. O. 1959. Some ecological characteristics of ants in New Guinea rain forests. Ecology 40: 437-447.

Valentine, B. D. 1986. Grooming behavior in Embioptera and Zoraptera (Insecta). Ohio Journal of Science 86(4): 150-152.

Information on the Internet

• The Zoraptera Database