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Immature Stages of Carabidae

Carabids are largely nocturnal and terrestrial, although a number of species are arboreal. Most species are predaceous as adults and larvae on a variety of hosts, mostly insects, but some species also attack snails and earthworms. Several species are associated with ants and termites, and a few species are questionably phytophagous and others at times utilize plant food in addition to the normal insect diet (Clausen 1940/1962). Entomophagous species more frequently attack the larvae and naked pupae of Lepidoptera than the immature stages of other insects. Several species are obligatory, primary, solitary ectoparasitoids, and a few species feed on seeds. Species that have developed obligatory external parasitism, show a degeneration in the larval instars following the first molt.

Carabids are generally beneficial, and have been considered vital in natural control of other insects, such as certain pestiferous Diptera (Legner et al. 1980). Nevertheless, they have not been used extensively in biological control. European species of the genus Calosoma have been introduced into North America as predators of the gypsy moth and brown-tailed moth.

As implied by the common name, "ground beetles," adults are mainly ground dwellers, and they carry on their activities principally at night. They may be found in various protected locations, such as under debris, loose bark of trees and stones, or they may inhabit distinct burrows. Many others, such as the genera Lebia and Calosoma are to some extent arboreal, where they may be frequently found attacking foliage-feeding insects in trees.

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In a few species the newly hatched larva does not feed for several days after hatching, because its nutrition is provided by yolk derived from the egg, which is contained in the digestive tract. Preoral digestion occurs among some larvae, as is found also among adults, whereas others ingest tissues directly. The injection of an intestinal secretion associated with preoral digestion has a paralyzing effect on the prey, which is important when the prey is large. The amount of food consumed by a larva is often large compared with its size. Burgess (1911, 1917) and Burgess and Collis (1915), studying C. sycophanta, found that each larva consumed an average of 41 6th instar gypsy moth caterpillars during its feeding period, covering ca. 14 days. Pairs of adults were found to destroy 100-460 6th instar larvae between the time of emergence of the beetles in springtime and the completion of feeding in midsummer.

Regardless of where they feed, Carabidae pupae in cells in the soil, often at a great depth. Therefore, C. sycophanta under normal field conditions forms its pupal chamber 10-12.5 cm. beneath the surface, but sometimes it penetrates deeper. This ensures a considerable degree of temperature and humidity uniformity, which is essential for pupae not tolerant of a wide range of these conditions. When a species is found to pupate above the ground, it is parasitic, such as Brachinus, which pupates in the pupal cell of its host.

The parasitic mode of development has been found in several carabid genera that are widely separated taxonomically. This relationship with the host was first recorded by Wickham (1894) for Brachinus janthinipennis Dej. and later also found by Dimmock & Knab (1904). The larvae occur in the pupal cells of Dineutes assimilis Aubé and show modifications in form, such as a reduction of the legs to a nonfunctional state, which is typical for the parasitic life style. A detailed account of parasitic development was given by Silvestri (1904) for Lebia scapularis Fourc. Adult beetles feed on all immature stages of the elm leaf-beetle, Galerucella luteola Mull, while larvae are restricted to attacking pupae. The 1st instar larva does not differ much from others of the family in being elongate, with 13 body segments, each of which bears sclerotized plates, and the legs are long and well-developed. There are 4-jointed caudal cerci. After finding the host pupae in the soil, the young larva feeds voraciously through a large puncture which it makes in the integument and in which the head is embedded. After the first molt, a grublike form is assumed in which the segmental plates and the caudal cerci are lacking, and the legs are reduced to short conical processes (see Clausen, 1940 for diagrams). This is followed by the prepupal and pupal stages, in both of which the meso and metathoracic segments are very much produced laterally. Before the larvae finish feeding, they spin a lemon-yellow or brown cocoon, which is composed of a mass of interwoven strands cemented together. While spinning, the remains of the host pupa may be drawn into the cocoon and enclosed within it. There are two generations annually, and overwintering is in the adult stage in sheltered areas.

Salt (1928) observed the behavior of Pelecium sulcatum Guer., one of an aberrant genus of Carabidae. Several larvae were found on various hosts, including beetle pupae and millepedes. Development was quick and apparently was completed on an individual host, so that in its essential aspects the mode of life was identical to Lebia, though no distinctive 2nd instar larva as found and no cocoon was made.

Arsinoë grandis Per. seems to represent a transitional phase between predation and parasitism (Blair 1927). Larvae attack those of the lichen-feeding tenebrionid, Catamerus revoili Fairm., in Nyasaland. Several larvae of the latter were found to bear those of Arsinoë attached by the mandibles to the abdominal dorsum. Feeding occurred in this position until the host died, after which the larva released its hold and searched for another host. Younger larvae may feed for as long as 2 weeks before causing the host's death, while later instars do so in 1-2 days. They pupate in the soil, and the duration of larval life was thought to be rather long, for some individuals that were collected did not enter the soil for pupation until several months later. This indicates that a number of host individuals are required during the feeding period.

Generally it may be concluded that carabid eggs are laid in the immediate vicinity of the hosts on which the larvae fed, though not closely associated therewith. The behavior of parasitic species in this regard does not differ much from that of predaceous species. Most species lay their eggs singly in small holes in soil with the ovipositor. Pterostichus multipunctatus Dej. is known to place a cluster of eggs in the soil chamber and then to guard it during incubation and for a while after hatching (Clausen 1940/1962).

Several species of Galerita, Chlaenius and Brachinus lay the eggs singly in mud cells which are constructed on plant leaves, stems, stones, etc. (Riley 1884, King 1919). The form and composition of the cells, as well as their location, are distinctive for the genus. Cells of Brachinus are crescentric or triangular and are located in groups of 3-10 on the undersides of twigs, plants stems and stones, while those of Galerita are triangular or purse-shaped, with a finely granular surface, and are formed on the undersides of smooth leaves. They are oblong and smoothly convex in C. impunctifrons Say, and are similarly placed on the undersides of smooth leaves. Those of C. aestivus Say are found on dead twigs, plants stems, the bark of trees, etc. While forming the cell, the mud pellet is first collected about the tip of the abdomen of the female beetle, and the walls are built upon on the stone or other surface in the form of a mold about the caudal segments. The cover is formed from the mud carried on the dorsum of such segments (Clausen 1940/1962).

Craspedonotus tibialis Schaum., inhabiting sand duns in Japan, shows an elaborate provision for laying eggs (Clausen et al. 1927). The female beetle digs a burrow 25-45 cm. deep, inclined at an angle of 45°, in embankments, and the eggs are laid singly in small chambers branching off from the main burrow. The entire egg-laying period is thought to be passed in the burrow, except for regular trips in search of food.

Life cycles in Carabidae are very variable, ranging from several months in Lebia grandis to several years. Most species probably have an annual cycle, with winger being passed as adults, although in many species adult beetles may live for several years. Calosoma sycophanta adults usually pass two winters, and sometimes 3-4, though none are known to lay eggs for more than two seasons (Burgess 1911, 1917). Males and females both live the same length of time. The adult stage is reached late in the season, and oviposition does not start until the following spring, with some individuals not ovipositing until the second season. Studies on a large number of C. sycophanta showed that an average of 128.5 eggs were laid per female, with a maximum of 653. However, the average for Carabidae is thought to be much lower than this (Clausen 1940/1962).