Immature Stages of Chrysopidae
Larvae, or "aphis lions," and adults of all chrysopids are predaceous, usually feeding on aphids, whiteflies, mealybugs and other soft-bodied insects and mites. Eggs are stalked and the size, shape and surface features of the egg are diagnostic. Larvae are distinguished in some species by their habit of carrying a packet of trash over the dorsum, which is renewed after the molt. They pupate in white, spherical, silken cocoons, which usually are attached to the underside of leaves.
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.
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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 which, 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.
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.