File: <chrys1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
Enemy Groups > <Citations> |
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. Please CLICK on
picture to view details: 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. References: Please refer to <biology.ref.htm>, [Additional references may be found at: MELVYL Library ] |