Description & Statistics
Chrysopids are considered wholly beneficial and have been used in augmentation release programs against homopterous pests throughout the world. A number of species of Chrysopa were introduced to New Zealand for use in the control of aphid and mealybug pests and also against Chermidae attacking pines (Clausen 1940/62).
Chrysopidae feed on a variety of soft-bodied insects, but mostly on aphids and mealybugs. Leafhoppers, thrips, lecaniine Coccidae, mites, etc., may also be attacked. Extensive feeding occurs at intervals on eggs of Lepidoptera. Larvae of Chrysopa rufilabris Burm. have been found to pierce leaf tissue with the mandibles in order to feed on larvae of Agromyza jucunda v.d.W. in their mines. This species is a valuable predator of red mites on cotton, the larvae consuming an average of 80 per day during the entire developmental period (Clausen 1940/62). Generally, adults feed on the same insects that serve as prey for larvae, although their activities in this respect are less. Extended early accounts of the biology and behavior of Chrysopidae are by Wildermuth (1916), Smith (1921, 1922b) and Withycombe (1923).
Adults usually live 4-6 weeks. Oviposition occurs the day following emergence from the cocoon and mating, but occasional species pass the winter as adults and oviposit the following spring and summer. Killington (1935) referred to a spermatophore being produced at mating by Nathanica fulviceps Steph., although Withycombe (1923) did not find one. The number of eggs laid by the different species varies, the maximum being recorded by Smith of 617 by a female of Chrysopa occulata Fitch in 42 days. The general average is thought to be 100-200. Killington (1936) cited oviposition records, among which are those by Okamoto of 550 eggs from C. nipponensis Okam. and by Withycombe of 480 eggs from a female of C. phyllochroma Wesm.
The eggs of all species are similar in form, being oblong in outline, with a small micropylar structure at the anterior end. They are usually borne at the ends of filamentous but rigid stalks. There is a lot of variation in the form of the stalk itself and the position in which it is placed. The length of the stalk varies directly with the length of the female's abdomen (Smith 1921, 1922b). In the larger species the maximum length is ca. 15 mm. Some species lay their eggs singly or in small groups on the underside of leaves, but C. albolineata Kill. places them at the edge, with the stalks in the same plane as the leaf. Chrysopa flava Scop. and C. flavifrons Brauer lay the cluster of eggs, numbering up to 40, on a common stalk, from the tip of which they radiate like a brush (Withycombe (1923). The stalk really represents a number of individual stalks which have fused. In Notochrysa capitata F. the eggs are placed radially on pine needles, and the stalks are knotted at regular intervals, or moniliform. The provision of a stalk on which the eggs are borne is thought to be for protection. However, this is not entirely successful, for newly hatched larvae often feed on the still unhatched eggs, and they may be parasitized by several species of Scelionidae. Williams (1931) found that the numerous species of Anomalochrysa, native to Hawaii, have elongated oval eggs which are laid on the foliage and lack the stalk entirely (see Clausen, 1940 for diagrams). Eggs are white or pale yellowish-green when freshly laid, but change to bluish-green and finally to gray before they hatch.
The newly hatched larvae of C jacobsoni v.d.W. return to the egg cluster during the first two nights after hatching and remain head downward on the stalks (Jacobson 1912).
The three larval instars do not differ very much. Each has a rather elongated body, with 9 abdominal segments, and is clothed with hairs that, in trash-carrying species, are hooked at the apex. The head is flat, and the gigantic sickle-like jaws and the maxillae extend directly forward. The mandible and maxilla on each side are held together by a flange which fits into a groove, which forms a sucking tube through which the body fluids of the host are removed. The true mouth seems to be completely closed.
Carrying a packet of trash dorsally over the body serves as a means of distinguishing the larvae of certain species of the family from those of Hemerobiidae. These larvae have the abdomen arched and shortened. The packet is rebuilt after each molt. Various materials such as host remains and debris, are used in its construction. In C. lineaticollis Fitch the larva first thrusts its head beneath the bit of debris and then utilizes the jaws in working it backward to the thorax. The numerous fragments are a bit woven together and are forced backward as new additions are made at the front. The anterior half of the packet is free but rests on the thoracic tubercles (Smith 1921, 1922b). In other species the fragments are thrown backward over the dorsum and are not fastened together. Species carrying trash packets live almost entirely in the open, and the adaptation is thus considered to be for protection. When mature, the larvae of some species seek protected places for pupation, while others spin the cocoon on the flat leaf surface (Clausen 1940/62).
The oval, parchment-like cocoon is formed from silken strands produced by modified Malpighian tubules and released through the anal opening. The pupa pushes off the hinged lid at the time of emergence rather than being cut with the mandibles. Jacobson (1912) found that the larva forms this lid at the time of cocoon formation, but other researchers are uncertain regarding the way it is formed. The pupa lies curled within the cocoon and becomes active only a short time before adult eclosion. It is able to inflate its body to several times the original volume, thus facilitating the opening of the cocoon lid, after which it crawls out, wanders about for 1-2 hrs. and then transforms to the adult. Some individuals pass through the pupal stage without forming a cocoon. In multibrooded species, overwintering adults are somewhat brownish as contrasted with the green of the summer broods. This seasonal color change is comparable to that found in Hemerobiidae.
Life cycles of Chrysopidae are influenced by climate, and marked differences occur for the same species under summer conditions in various sections and countries. Generally, the development from egg to adult takes ca. one month. Wildermuth (1916) recorded the duration of the egg, larval and cocoon stages of C. californica Coq. as 6-12, 11-22 and 14-23 days, respectively. Eggs of C. rufilabris hatch in 3-5 days, and the larval and cocoon stages require 18 and 6 days, respectively. Hibernation may be in any stage except the egg, although most pass the winter in the larval or prepupal stage within a cocoon. Chrysopa californica, C. carnea Steph., and C. ploribunda Fitch hibernate as adults in protected spots. The generations per year vary, ranging from only one for C. albolineata in England to at least 6 for C. californica in Arizona.
Chrysopidae is a moderately large, worldwide family with more than 802 species known by 2000. There are about. 87 species in North America. Diagnostic characters of these include a long antennae, slender and tapering at the apex, a forewing with 12 or more cross-veins between R-1 and R-2, costal cross-veins not formed, and S-c and R-1 not fused at apex of wing. Chrysopids are usually green with golden or copper-colored eyes. Species of Eremochrysa in western North America are often tan, resembling hemerobiids. Some species produce a disagreeable odor.
The larvae and adults of all chrysopids are predators that usually feed on aphids, whiteflies, mealybugs and other soft-bodied insects and mites. Some adults feed on pollen (Meleoma) and others on honeydew (Eremochrysa). The eggs are stalked and the size, shape and surface features of the egg are diagnostic. The larvae of some species transport a packet of debris, which is renewed after the molt. They pupate in silken cocoons that usually are attached beneath leaves
Further Behavior & Description
Green lacewings are insects in the large family Chrysopidae of the order Neuroptera. There about 87 genera and (differing between sources) 1,300–2,025 species in this widespread group. Members of the genera Chrysopa and Chrysoperla are very common in North America and Europe; they are very similar and many of their species have been moved from one genus to the other times and again, and in the non-scientific literature assignment to Chrysopa and Chrysoperla can rarely be relied upon. Since they are the most familiar neuropterids to many people, they are often simply called "lacewings". But actually most of the diversity of Neuroptera are properly referred to as some sort of "lacewing", so common lacewings is preferable.
Green lacewings are fragile insects with a wingspan of 6 to over 65 mm, though the largest forms are tropical. They are characterized by a wide costal field in their wing venation, which includes the cross-veins. The bodies are usually bright green to greenish-brown, and the compound eyes are conspicuously golden in many species. The wings are usually translucent with a slight iridescence; some have green wing veins or a cloudy brownish wing pattern. The vernacular name "stinkflies", used chiefly for Chrysopa species but also for others (e.g. Cunctochrysa) refers to their ability to release a vile smell from paired prothoracal glands when handled.
The adults have tympanal organs at the forewings' base, enabling them to hear well. Some Chrysopa show evasive behavior when they hear a bat's ultrasound calls: when in flight, they close their wings (making their echolocational signature smaller) and drop down to the ground. Green lacewings also use substrate or body vibrations as a form of communication between themselves, especially during courtship. Species which are nearly identical morphologically may sometimes be separated more easily based on their mating signals. For example the southern European Chrysoperla mediterranea looks almost identical to its northern relative Chrysoperla carnea, but their courtship "songs" are very different; individuals of one species will not react to the other's vibrations.
Adults also are crepuscular or nocturnal. They feed on pollen, nectar and honeydew supplemented with mites, aphids and other small arthropods, and some, namely Chrysopa, are mainly predatory. Others feed almost exclusively on nectar and similar substances, and have symbiotic yeasts in their digestive tract to help break down the food into nutrients.
Larvae have either a more slender "humpbacked" shape with a prominent bulge on the ., or are plumper, with long bristles jutting out from the sides. These bristles will collect debris and food remains – the empty integuments of aphids, most notably – that provide camouflage from birds.
The eggs are deposited at night, singly or in small groups; one female produces some 100–200 eggs. Eggs are placed on plants, usually where aphids are present nearby in numbers. Each egg is hung on a slender stalk about 1 cm long, usually on the underside of a leaf. Immediately after hatching, the larvae moult, then ascend the egg stalk to feed. They are voracious predators, attacking most insects of suitable size, especially soft-bodied ones (aphids, caterpillars and other insect larvae, insect eggs, and at high population densities also each other). Therefore, the larvae are colloquially known as “aphid lions” (also spelled "aphidlions") or “aphid wolves,” similar to the related antlions. Their senses are weakly developed, except that they are very sensitive to touch. Walking around in a haphazard fashion, the larvae sway their heads from one side to the other, and when they strike a potential prey object, the larva grasps it. Their maxillae are hollow, allowing a digestive secretion to be injected in the prey; the organs of an aphid can for example be dissolved by this in 90 seconds. Depending on environmental conditions, larvae need about 1–3 weeks to pupation which takes place in a cocoon; species from temperate regions usually overwinter as a prepupa, though Chrysoperla carnea overwinters as newly-hatched adults.
Some green lacewings will feed on only about 150 prey items in their entire life, in other cases 100 aphids will be eaten in a single week. Thus, in several countries, millions of such voracious Chrysopidae are reared for sale as biological control agents of insect and mite pests in agriculture and gardens. They are distributed as eggs, since as noted above they are highly aggressive and cannibalistic in confined quarters; the eggs hatch in the field. Their performance is variable; thus, there is a lot of interest in further research to improve the use of green lacewings as biological pest control.
Lacewings and their their larvae may be attracted to gardens by using companion plants. They are attracted by angelica, dill, coreopsis, cosmos, sunflowers, and the beneficial weed, dandelion.
For long, green lacewings were considered close relatives of the pleasing lacewings (Dilaridae) and brown lacewings (Hemerobiidae) and placed in the superfamily Hemerobioidea. But this grouping does not appear to be natural and misled most significantly by the supposed hemerobioideans' plesiomorphic larvae. Today, the Hemerobioidea are usually considered monotypic, containing only the brown lacewings; the green lacewings seem to be very closely related to the osmylids (Osmylidae), which have much more advanced larvae superficially resembling those of the spongillaflies (Sisyridae) with which the spongillaflies were thus formerly allied. Thus, though the superfamily Osmyloidea is often considered monotypic these days too following the spongillaflies' removal from there, it is arguably better to include the osmylids as well as the green lacewings there.
Banks, N. 1903. A revision of nearctic Chrysopidae. Trans. Ent. Soc. Amer. 29: 137-62.
Smith, R. C. 1922. The Biology of the Chrysopidae. NY. Agr. Expt. Sta. Mem. 58: 1232-1372.
Withycomb, C. L. 1923. Notes on the biology of some British Neuroptera (Planipennia). Trans. Ent. Soc. London (1922): 501-94.