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Neuroptera

(Lacewings)

Class Insecta

Order Neuroptera

Number of families 17

Photo: A mantisfly (family Manitispidae) near the Bayer River of Papua New Guinea. (Photo by George D. Dodge & Dale R. Thompson. Bruce Coleman, Inc. Reproduced by permission.)

Evolution and systematics

Neuroptera represents one of the oldest and most archaic lineages of endopterygote (= holometabolous, or undergoing complete metamorphosis) insects. The oldest known fossils of Neuroptera suggest that the group had its origin in the early Permian period, with significant family level diversification in the late Triassic and early Jurassic. At the end of the Jurassic, however, all extant lineages had appeared, and at least three lineages (14 families) had become extinct. Truly spectacular lacewings that we know only from fossils include

Kalligramma haeckelli and Lithogramma oculatum (Kalligrammatidae, Upper Jurassic), two species with distinctive eyespots in their large, brightly colored wings. Numerous families of lacewings are known only from fossils, including Kalligrammatidae, Nymphitidae, Permithonidae, Mesopolystoechotidae, Solenoptilidae, Allopteridae, and Osmylitidae. Moreover, many described fossil lacewings can be placed in extant families, including Permithonopsis obscura (Polystoechotidae), Embaneura vachrameevi (Psychopsidae), Plesiorobius (Berothidae), and Euporismites balli (Osmylidae).

Neuroptera comprises 17 extant families containing more than 6,000 species worldwide divided into three superfamilies. Myrmeleontidae (more than 2,000 spp.) and Chrysopi-

dae (more than 1,200 spp.) are the most species-rich families, followed by Hemerobiidae (about 550 spp.) and Ascalaphidae (some 400 spp.). The superfamily Nevrorthiformia, with the single family Nevrorthidae, represents the most basal group; members of this family are sporadically found in Japan, Taiwan, Australia, and Europe. The Myrmeleotiformia contains five families (Myrmeleontidae, Ascalaphidae, Nemopteridae, Psychopsidae, and Nymphidae). It is a well-defined group of generally large lacewings with soil-dwelling or arboreal larvae. The Hemerobiiformia, made up of 11 families (Hemerobiidae, Chrysopidae, Sisyridae, Berothidae, Mantispidae, Rhachiberothidae, Ithonidae, Polystoechotidae, Dilaridae, Coniopterygidae, and Osmylidae), is a morphologically diverse assemblage of lacewings, many of which have unique and highly specialized life cycles. Ithonidae are robust, mothlike lacewings with fossorial, scarab-like larvae associated with roots of trees and bushes (e.g., creosote). This family and the sister family Polystoechotidae sometimes are considered the most basal clade of lacewings. Another clade, or group of closely related families, is the Dilaridae clade. This group comprises Dilaridae, Rhachiberothidae, Mantispidae, and Berothidae and is united by particular larval head characteristics.

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Order: Neuroptera

Antlion larvae (Myrmeleon spp.) make traps. (Illustration by Barbara Duperron)

Physical characteristics

Lacewing is a common name that describes the lace-like venation pattern of the relatively large, delicate wings of most adult Neuroptera. The adult body shape is relatively uniform across the order. The head is well defined, typically without setae or bristles (although dense tufts of long setae are found in many Ascalaphidae). The eyes are large, well defined, and spherical in shape; some ascalaphids have a horizontal sulcus (line) dividing the eyes into upper and lower regions. Welldefined ocelli (simple eyes) are present on the vertex only in the family Osmylidae. The mouthparts are chewing and directed either anteriorly or ventrally; in many Nemopteridae the mouthparts are extremely elongated. Antennae typically are very elongate and moniliform (simple) and rarely flabellate (Dilaridae); sometimes they have apical clubs (Ascalaphidae) or are thickened (Myrmeleontidae).

The thorax is divided into three segments, the posterior, wing-bearing segments being much larger than the anterior segment. Legs usually are slender and elongate; forelegs sometimes are raptorial (Rhachiberothidae and Mantispidae). The wings almost always are large and broad and rarely are reduced. Some species are brachypterous or apterous. The wing shape is elongate and oblong to elliptical or ovate; the margin either is round or falcate (hooked or curved). Venation is highly reticulate in most groups, although it is reduced to only a few veins in some (Coniopterygidae). The abdomen usually is long, and the genitalia on terminal segments either are reduced and concealed (Myrmeleontidae) or elaborate and exposed (Osmylidae and Nymphidae).

Larval body shape typically is campodeiform or, rarely, scarabaeiform. The head is dorsoventrally flattened, with mouthparts projecting anteriorly. The mouthparts are mod-

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ified uniquely, such that the buccal (mouth) cavity is closed and sucking tubes are formed laterally by the interlocking of the mandibles and maxillae. Jaws are elongate, simple, or toothed and used to impale prey and suck out its contents. In Sisyridae and Osmylidae the jaws are extremely long and slender. In Myrmeleontiformia the jaws often are held open at more than 180 degrees and snapped closed to trap prey. Eyes comprise a group of five, six, or seven stemmata (rudimentary eyes), but eyesight is poor.

Antennae either are short or elongate. The thorax usually is short and broad, but in some Nemopteridae, the prothorax (anterior segment) may be lengthened into a neck. Legs are long in the active arboreal larvae (Chrysopidae), short in fossorial larvae (Myrmeleontidae and Ascalaphidae), or rudimentary in egg sac predators (Mantispidae). The abdomen may be elongate or ovate. The thorax and abdomen often have fleshy lateral projections (scoli) (Nymphidae) or long and recurved (Chrysopidae) or ornately shaped (Ascalaphidae) setae used to hold items of debris on the dorsum. Another unique characteristic of neuropteran larvae is that the midgut is discontinuous with the hindgut; solid waste is not passed until the adult emerges from the pupal case with a fully formed digestive system. Larvae spin pupal cases with silk produced from modified Malphigian tubules. The pupa is exarate and decticous and emerges from the pupal case to molt into a fully winged adult.

Distribution

Neuropterans are distributed throughout tropical and temperate regions, with the greatest species richness and diversity in the tropics. Several families (Myrmeleontidae, Chrysopidae, Hemerobiidae, Coniopterygidae, Mantispidae, and Ascalaphidae) are distributed widely, although particular subfamilies, genera, and species within each family are much more restricted. From fossil evidence it is clear that the former distribution of some groups was more extensive than today. Nemopteridae is a group of lacewings distributed throughout Africa, the Palaearctic region, Australia, and South America but absent in North America (although a fossil nemopterid has been found in Colorado). Psychopsidae are restricted to Africa, Asia, and Australia, while Nymphidae are found only in the Indonesian Archipelago, Papua New Guinea, and Australia. Some groups have highly disjunct, apparently relict distributions, also evidence of more extensive past distributions. Nevrorthidae, comprising 10 species with aquatic larvae, are found in Australia, Japan, Taiwan, and the Mediterranean region. Ithonidae (including Rapismatidae) are diverse in Australia but also are found in mountainous regions of Central America and Asia and in the southwestern United States.

Habitat

Lacewings are found in a wide variety of habitat types, from arid desert plains to montane rainforests. While adults typically are found on vegetation, larvae are more specific in their habitat requirements and often are associated with a particular substrate or prey type. Families such as

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Myrmeleontidae and Nemopteridae, with larvae that live in sandy soils, are adapted for existence in deserts and dry savannas and are particularly diverse and numerous in these regions around the world. Larvae of some species of antlion (Myrmeleontidae: Acanthoclisinae) can swim through loose sand in search of prey. Some lacewings, such as Chrysopidae and Hemerobiidae, are strictly arboreal as larvae on trees, shrubs, and grasses. Larvae of Psychopsidae are recorded inhabiting deep crevices in Eucalyptus spp. trees in dense forests in Australia. Larvae and adults of Coniopterygidae are found on foliage of trees and bushes, including some specific to particular vegetation types (e.g., Aleuropteryx juniperi). Larvae of both Nevrorthidae and Sisyridae are predators in freshwater streams, while larvae of some Osmylidae (e.g., Osmylus fulvicephalus in Europe and unidentified Kempyninae in Australia) live in the littoral zone of such streams under rocks and among leaf litter. Larvae of moth lacewings (Ithonidae) are fossorial, living among the roots of trees and shrubs. One example is Oliarces clara, the only North America ithonid, which is associated with the roots of the creasote bush (Larrea tridentata).

Order: Neuroptera

Antlions (family Myrneleonidae) live in the savanna of southern Africa. (Photo by Michael Fogden. Bruce Coleman, Inc. Reproduced by permission.)

Behavior

Several neuropteran families possess various anatomical characteristics that apparently are involved in chemical communication between sexes during courtship. Males of Nevrorthidae and some Myrmeleontidae possess eversible pleurocavae on the abdomen, whereas males of Nemopteridae have a bulla on the wing margin or wing base; both are used to disperse chemical pheromones. Males of some Mantispidae possess an Eltringham organ on the abdomen, which also is used in the dispersal of mating chemicals. There is complicated communication among Chrysopidae involving abdominal vibrations (Chrysoperla) or wing “rapping” (Mallada spp.), resulting in complex “calls” that are communicated via the substrate. Various defensive behavioral mechanisms are employed by different lacewings to evade or deter predators.

While most adult neuropterans remain inactive during the day, relying on camouflage to escape detection, some engage in various forms of behavior to make the deception more complete. The families that have setae holding items of debris on the dorsum use this “trash packet” as camouflage and as a shield against predators. Beaded lacewings (Berothidae) commonly begin gently swaying when a potential predator is detected, apparently to simulate a twig being moved by a breeze. When disturbed, certain lacewings feign death (some Hemerobiidae and Chrysopidae), whereas others emit an offensive odor (Nymphes spp. of Nymphidae and Plesiochrysa spp. of Chrysopidae). Some Mantispidae (Euclimacia spp. and Climaciella spp.) are effective mimics of paper wasps (Vespidae) in color and shape and also adopt postures and movements resembling the paper wasp when disturbed. Some first instar larvae of Mantispidae have been shown to follow a series of obligatory behavioral cues when searching for a suitable host spider egg sac. Larvae of Climaciella brunnea must board an adult spider before they enter the egg sac. If placed on a spider and not allowed to board, they simply climb to the highest point of the spider and assume a questing posture to look

for another passing spider they can board. Upon hatching, larvae of Ascalaphidae and Nymphidae (Nymphes) group together for a period of time with jaws outstretched in an apparent defensive posture.

Feeding ecology and diet

Lacewings typically are generalist predators as larvae and adults, although there are exceptions; in several families, the larva has become highly specialized in its feeding ecology and diet. Many lacewing adults may be generalist omnivores, feeding opportunistically on soft-bodied insects, pollen, and honeydew. Adults of Nemopteridae and some Chrysopidae are obligate feeders on pollen and nectar from flowers, with many nemopterids having greatly elongated mouthparts modified for insertion into flowers with long corollas (where separate or fused flower petals come together and often form a long tube). Predatory adult Mantispidae and Rhachiberothidae have raptorial forelegs for seizing and holding prey, and many adult antlions (Myrmeleontidae: Acanthoclisinae) and owlflies (Ascalaphidae) have elongated claws and long, stiff bristles and spines on their legs for capturing prey in flight.

In most families the larvae are either sedentary “sit-and- wait” predators, waiting for hapless prey to walk into their open jaws (Ascalaphidae and Nymphidae), or active foragers, scouring the tactile landscape in search of prey items (Chrysopidae, Hemerobiidae, and Coniopterygidae). Larvae of some antlions (Myrmeleontidae: Myrmeleon spp.) construct conical pits in the sand and wait at the bottom with only their large jaws exposed. When a suitable prey falls into the pit, the antlion larva tosses sand upward with its head to dislodge the prey, so that it falls into its open jaws and then is dragged beneath the surface of the sand to be consumed. Larvae of Ithonidae and, presumably, Polystoechotidae are the only non-carnivorous lacewings, with short blunt jaws not suitable

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Order: Neuroptera

A green lacewing (Chrysopa) resting on seeds of black bindweed in Europe. (Photo by Kim Taylor. Bruce Coleman, Inc. Reproduced by permission.)

for impaling prey as other lacewings do. On the contrary, Ithonid larvae feed on root exudates of trees and bushes.

Among the families with aquatic larvae, Nevrorthidae are generalist predators in fast-flowing streams, while spongilla flies (Sisyridae) are obligate specialist predators of freshwater sponges and bryozoans. Sisryid larvae have highly modified jaws that are extremely long (often longer than the body) and narrow and are used to pierce individual cells of their sponge prey delicately. Semiaquatic larvae of Osmylidae use their long jaws to probe the wet soil and mud in search of softbodied prey, for example, larvae of Chironomidae (Diptera). Larvae of some families (Dilaridae, Osmylidae, and Psychopsidae) live under bark and in deep bark crevices, where they are generalist predators on a variety of arthropods living there. Beaded lacewing (Berothidae) larvae live as specialized predators on subterranean termites. Fragmentary evidence suggests that the larvae either secrete an allomone or inject a neurotoxin to immobilize their termite prey, on which they then can feed safely. The first and third instar larvae actively feed on termites, but the second instar is an inactive resting stage.

Larvae of Mantispidae are obligate, specialized predators on either social hymenoptera nests (Symphrasinae) or spider egg sacs (Mantispinae). In larvae that prey on spider eggs sacs, the active first instar triungulin larva seeks out a suitable host spider, which it boards and ultimately enters the egg sac. Once it is in the egg sac, the second and third instars take on a physiogastric form (i.e., hypermetamorphic development, or dramatic change in overall morphological features between instars). The larvae also may arrest the development of the spider eggs by chemical means to prevent them from hatching. There appears to be some level of host specificity.

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Reproductive biology

Mating either is brief or takes place over an extended period of time, usually through solitary encounters between the sexes. Mating swarms have been recorded for Ithone in Australia and Oliarces in the United States. Eggs are laid either solitarily or in batches on substrate, in crevices, or on silken stalks (certain Nymphidae, Mantispidae, and Chrysopidae). Ascalaphidae often deposit infertile eggs (repagula) between their fertile eggs and the probable path of potential egg predators. Some species of Mantispidae lay hundreds of eggs, presumably because of the high mortality rate faced by the minute first instar larvae as they seek out suitable spider egg sacs. There is little or no parental care after oviposition.

Conservation status

Owing to the often high degree of regional endemicity and low degree of vagility, many neuropterans are particularly vulnerable to extinction from pollution and habitat alteration by human activities. Other species are large and brightly colored (Libelloides spp. and Nemoptera spp.), making localized populations susceptible to being overly collected by amateur collectors. At present no species of lacewing is listed by the IUCN worldwide. In various countries around the world, there are national, state, or local regulatory lists of protected species or populations of neuropterans.

In the United States several species of neuropterans are considered endangered, with legislated protection in some states (e.g., California and Hawaii). These species include

Nothochrysa californica (Chrysopidae), Oliarces clara (Ithonidae),

Owlfly (family Ascalaphidae) larva in the Costa Rican rainforest. (Photo by Michael Fogden. Bruce Coleman, Inc. Reproduced by permission.)

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Distoleon perjerus (Myrmeleontidae), Pseudopsectra usingeri

(Hemerobiidae), and three species of Micromus (Hemerobiidae). In South Africa species of lacewing considered critically endangered due to habitat destruction include Pamexis bifasciatus, P. contamminatus, Exaetoleon obtabilis (all Myrmeleontidae); Sicyoptera dilatata, S. cuspidata, Halterina pulchella; and H. purcelli (all Nemopteridae).

Significance to humans

As beneficial generalist predators, lacewings from at least three families (all with arboreal larvae) have been used in

Order: Neuroptera

biological control of arthropod pests in agriculture. Coniopterygidae have long been recognized to have considerable potential for biological control, particularly of spider mites (Tetranychidae) in greenhouses and orchards. Two families, Chrysopidae and Hemerobiidae, are used on a commercial scale to control arthropod pests in numerous field and greenhouse crop situations. Chrysopids from various genera (Mallada, Chrysoperla, and Chrysopa) are reared in large numbers in commercial insectaries for inundative release among various crops for successful control of many arthropod pests. Hemerobiids also are reared for inundative release but are used less commonly in commercial situations.

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1. Green lacewing (Mallada albofascialis) adult; 2. Green lacewing (M. albofascialis) eggs; 3. Green lacewing (M. albofascialis) larva; 4. Antlion (Myrmeleon formicarius) larva; 5. Beaded lacewing (Spermophorella maculatissima); 6. Spoonwing lacewing (Nemoptera sinuata); 7. Mantid lacewing (Euclimacia torquata); 8. Moth lacewing (Megalithone tillyardi); 9. Norfolius (Norfolius howensis). (Illustration by Barbara Duperron)

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