Zoraptera

(Zorapterans)

Class Insecta

Order Zoraptera

Number of families 1

Evolution and systematics

Zoraptera is a small order of exopterygote neopteran insects, for which the only general common name is zorapterans, although "angel insects" occasionally has been used. The affinities of Zoraptera have long been debated, and the order has been regarded as distinct but difficult to place phylogenetically. The major point of contention is whether they are primitive Paraneoptera (and thereby allied with bugs, lice, and their relatives), are related to cockroaches (Blattodea), or perhaps are descendants of some pre-dictyopteran insect stock. Other suggested alliances, based in part on the presence of distinct cerci, are as a sister group of the termites (Isoptera) or the webspinners (Embioptera). Although it has not yet been studied for many species, wing structure allies them most closely with cockroaches and their allies, with recent authors believing them to be primitive Blattoneoptera that separated early from the main lineage. There are no known fossils, other than for one species (Zorotypus palaeus) from Dominican amber (Lower Miocene/Upper Eocene).

All Zoraptera have been placed in the single family Zorotypidae. Suggestions that the New World taxa may constitute a separate family, as yet unnamed, need further verification. Until recently, all the 30 described species were allocated to the single genus Zorotypus. In 1993 six additional genera (Brazilozoros, Centrozoros, Floridazoros, Latinozoros, Meridozoros, and Usazoros) were erected, based on wing venation. All of these genera contain one species and are from the New World. All Old World species are placed in Zorotypus. Zorotypus is now a "holding genus" for the many species for which venation is unknown. Species identification often is difficult, with the females of some species almost impossible to place without associated males.

Physical characteristics

Zoraptera are small, elongate insects, ranging from 0.08 to 0.16 in (2–4 mm) in length. All species are similar in appearance and require dissection and microscopic examination for accurate identification. Adults usually are brown but range from pale brown to almost black and typically are not strongly patterned. The nymphs are pale creamy brown. Two distinct body forms occur in both males and females: wingless individuals (by far the more common and frequently encountered form) and winged individuals, which are generally darker and hold the wings flat over the abdomen. Winged individuals can shed their wings like termites and are recognized by the small wing "stubs" that remain.

The hypognathous head, usually narrowed anteriorly, has chewing mouthparts and a pair of antennae with nine segments. Males of many species have a cephalic gland (fontanelle) on the dorsal surface of the head. Mandibles have several "teeth"; maxillary palpi have five segments, and labial palpi have three segments. The well-defined prothorax is more or less square, and the pterothorax is more developed in winged than in wingless forms. The wings are broad and elongate, with reduced venation, and the hind wing is considerably shorter than the forewing and has less venation. Wingless forms lack both compound and simple eyes (ocelli); winged forms have well-developed compound eyes and three simple eyes. The legs are unremarkable other than for the strongly broadened hind femora, which can bear a row of thickened spines. Their number and arrangement are of taxonomic relevance; the tarsi have two segments with two claws. The oval abdomen is somewhat flattened dorsoventrally, and the short, unsegmented cerci (posterior sense organs) usually have a long apical bristle. Female genital structures are simple, with a well-sclerotized internal spermatheca and a long spermathecal duct. Male terminal structures are more complex, often with distinctive genital details. The pattern of thickened bristles on the posterior apex of the abdomen is also distinctive; the most universal male genital feature is a hooklike projection used to link with the female during copulation.

Distribution

The order is distributed widely but predominantly is tropical and subtropical. Zoraptera occur on all continents but have not yet been found on mainland Australia. Their greatest diversity appears to be in the neotropics, with a few species known from North America, Southeast Asia, Africa, or the Pacific islands. Zorotypus hubbardi is widespread in the southeastern United States and ranges northward to beyond forty-one degrees north latitude.

Habitat

Zoraptera are predominantly subcortical and are thus found under the bark of dead and fallen timber. They appear to be most common in rotting wood and logs with loose bark but with the cambium relatively intact. Their presence may help identify a particular phase in wood decomposition. They sometimes occur with termites. Others are found in ground litter, and Z. hubbardi has been reported from piles of decaying sawdust on old milling sites in North America. Winged individuals occasionally are attracted to light or taken in flight interception traps.

Behavior

Zoraptera are gregarious and occur in colonies probably founded by single females. Although winged females have been seen to mate soon after they emerge, no such colony establishment has been noted in the wild. Social structure may be well defined, with formation of dominance hierarchies among males in Z. gurneyi. These hierarchies are determined in part by size and age, with older males becoming more dominant. Aggressive encounters between males of this species involve contact avoidance, head butting, grappling, chasing, and kicking. Grooming behavior, including mutual grooming, is well developed.

Feeding ecology and diet

Zoraptera are primarily fungus feeders, eating both hyphae and spores. Examination of the gut contents of particular species also has revealed arthropod fragments and pieces of wood. Two New World species, Z. barberi and Z. gurneyi, have been observed ingesting small nematodes. Captive zorapterans feed on yeast and crushed rat chow and may engage in cannibalism.

Reproductive biology

Zoraptera usually reproduce sexually. Males of some species are much rarer than the females. The Panamanian Z. gurneyi normally reproduces by parthenogenesis, although mating occurs when males and females meet. Males of Z. gurneyi are larger than females and may fight to gain access to females. The dominance hierarchy of this species may be pronounced and may represent a form of female defense polygyny. Females may mate every few days, either with the same male or with a variety of partners. In contrast, the smaller Z. barberi does not form hierarchies. Courtship involves nuptial feeding, by presentation of a drop of liquid secreted from the opening of the cephalic gland as a courtship gift. In mating of this species, the male is upside down, and copulation lasts for about one minute, occurring after periods of antennation. A single mating pair may copulate several times in succession. There appears to be no well-defined seasonal development in the tropics; eggs take several weeks to hatch. About four or five larval stages (instars) occur; the earlier stages have eight-segmented antennae. Adults may live for about three months.

Conservation status

Most species appear to be rare, with some known from single individuals and localities. Regional or local endemism is common for most species. No formal evaluation of conservation status has been advanced for any member of the order, and no species is listed by the IUCN or in any individual country legislation as having conservation significance. Occasionally, more local concerns (such as for Zorotypus swezeyi in Hawaii) have been expressed because of loss of habitat. No estimates of population size or trends in abundance are available for any species of the order.

Significance to humans

None known.

Species accounts

List of Species

Hubbard's zorapteran

Zorotypus hubbardi

family

Zorotypidae

taxonomy

Zorotypus hubbardi Caudell, 1918, Florida, United States.

other common names

English: Hubbard's angel insect.

physical characteristics

No superficial, macroscopic, specific characters; recognizable by distribution. Body length 0.10–0.11 in (2.6–2.9 mm). Color medium to dark brown.

distribution

Southeastern United States. The most widely distributed zorapteran in North America.

habitat

Under bark in moist logs and in sawdust piles on old mill sites.

behavior

Occurs in colonies that may persist for several years.

feeding ecology and diet

Feeds on fungal spores and hyphae; ingestion of other foods, such as arthropod fragments, may be fortuitous and may represent a more general scavenging habit.

reproductive biology

Bisexual or facultatively parthenogenetic. Oviparous, with four or five nymphal instars.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Choe, Jae C. "Zoraptera of Panama with a Review of the Morphology, Systematics and Biology of the Order." In Insects of Panama and Mesoamerica: Selected Studies, edited by D. Quintero and A. Aiello. Oxford: Oxford University Press, 1992.

Periodicals

Choe, Jae C. "Courtship, Feeding and Repeated Mating in Zorotypus barberi (Insecta: Zoraptera)." Animal Behaviour 49, no. 6 (1995): 1511–1520.

Gurney, A. B. "A Synopsis of the Order Zoraptera, with Notes on the Biology of Zorotypus hubbardi Caudell." Proceedings of the Entomological Society of Washington 40 (1938): 57–87.

Hubbard, M. D. "A Catalog of the Order Zoraptera (Insecta)." Insecta Mundi 4 (1990): 49–66.

Kukalová-Peck, Jarmila, and Stewart B. Peck. "Zoraptera Wing Structures: Evidence for New Genera and Relationships with the Blattoid Orders (Insecta: Blattoneoptera)." Systematic Entomology 18, no. 4 (1993): 333–350.

New, T. R. "Notes on Neotropical Zoraptera, with Descriptions of Two New Species." Systematic Entomology 3 (1978): 361–370.

Timothy R. New