Immature Stages of Staphylinidae
First instar larvae of Staphylinidae are not easily distinguished from those of the predaceous and scavenging species. These larvae first search in the soil to a depth of 2-15 cm until a Hylemya puparium is found, and it then penetrates the hardened shell. The puncture is sealed after entry. The body of newly hatched larvae is ca. 1.5mm in length, rather slender, and distinctly segmented, with 10 abdominal segments, of which the last two are darker in color and taper to a rounded point. The head is large and darker in color than the body, and the antennae are 3-jointed and well developed. Legs are normal for the family. The caudal cerci are shorter than those of most other species and are borne on short cylindrical processes dorsolaterally at the posterior margin of the penultimate segment.
Following entry of the host puparium, the larva begins feeding through a minute puncture made in the delicate cuticle of the pupa. The feeding position is frequently changed but apparently limited to the anterior dorsal region. When fully fed the body is considerably enlarged, the transparent intersegmental membranes being greatly stretched and the average length is ca. 2.0 mm (Clausen 1940/1962). Second instar larvae are markedly different from the first, being very degenerate as a result of the adoption of a parasitic mode of life. The body is glistening white, with the cuticle very lightly sclerotized, and the setae and cerci are absent. The legs are rudimentary and indistinctly segmented and lack the large terminal claw. Each of the last two thoracic and the first eight abdominal segments has a single pair of fleshy prominences at the dorsolateral margins. Feeding by this stage is extensive and very little movement occurs (Clausen 1940/1962). Third instar larvae are generally identical to second, but larger. There are also 9 pairs of spiracles situated between the first and second thoracic segments and on the first eight abdominal segments, respectively. in Aleochara and other genera that pupate outside the host puparium, the segmental tubercles or prominences are lacking. During the feeding period no excrement is voided with the exception of occasional minute drops of a clear fluid, and the mature larva casts the meconium. The host pupa is completely consumed, and the puparium becomes opaque because of the meconial covering on the inner surface.
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In summer the feeding period is complete in 5-6 days after the first molt and is followed by a quiescent stage of 12-18 days prior to the appearance of the pupa. The pupal stage also requires 12-18 days at the completion of which the adult beetle gnaws its way out of the puparium (Clausen 1940/1962). Adults are very active and feed extensively on cabbage maggots. There are apparently two generations/yr, corresponding to the cycle of the host, and the winter season is passed as a first-instar larva within the host puparium. The first brood of adults appears in May and June and the second in August and September.
Although most parasitic members of the family attack puparia occurring on or in the soil, occasional species find their hosts on or in plants. Maseochara valida Lec. was found by Coquillett (1891) to develop in the puparia of a syrphid fly, Copestylum marginatum Say, which develops in the semiliquid material in the decaying leaves of cactus. Kramer (1926) studying Aleochara curtula Goeze, parasitic in the puparia of Lucilia, etc., found that this species habits are generally similar to those of C. bilineata, except that the third instar larva assumes an active and more normal form, with the legs being large and well developed for locomotion; and it emerges from the puparium for pupation in a cell in the soil. This habit is found in the genera Aleochara, Baryodma, Polychara, and Maseochara, whereas the more degenerate form, which pupates within the host puparium, is found in Coprochara and Polystoma.
Baryodma bimaculata Grav. was noted by Lindquist (1936) to develop in the puparia of Sarcophaga and Cryptolucilia in Texas. The planidium enters the puparium in the same way as Coprochara, and emergence of the adult occurs ca. 20 days later. The field parasitization of these hosts is ca. 25%.
Observations recorded on other species of parasitic Staphylinidae suggest that the adults of these species are also important as enemies of the same pests because they are predaceous on both larvae and pupae (Clausen 1940/1962). Quayle (1913) recorded the habits of Somatium oviformis, a minute species that seems to feed mainly on red mites. This is true of both the adult and larval stages. The eggs are light orange in color and are laid singly on the undersides of the infested leaves. Larvae consume ca. 20 mites/day and adults about half as much. Mank gave an account of the habits and descriptions of the immature forms of a series of species predaceous on dipterous larvae occurring in decaying vegetable matter. These species belong to the well known genus Philonthus and related groups. Both adults and larvae feed extensively on maggots found in the medium in which they live. The life cycles of the different species are found to be relatively short (one month or less). The larvae of predaceous species are very active and aggressive. The body is elongate in form, and individuals may be readily distinguished from carabid larvae by the prominent two-jointed caudal stylets and by the single claw of the tarsi. They also generally lack the distinct heavily sclerotized segmental plates often found in Carabidae, although these plates are present in Tachinus. The most reliable character in distinguishing larvae of the family is the "upper lip," which varies in the number and size of the teeth borne at the anterior margin. The abdomen terminates in a relatively large "pseudopod" or "pusher," which is utilized in locomotion.
Clausen (1940) stated that the pupae present few distinguishing features, with the main character utilized is the fringe of hairs at the anterior margin of the thorax and those at the lateral margin of the abdomen. In Tachinus, the integument of the pupa is soft and the body is completely covered with a soft material which becomes silvery in appearance.
White & Legner (1966) give a detailed account of the biology of Aleochara taeniata Erichson, attacking muscoid flies. Legner & Warkentin (1991) considered species of Philonthus very important predators of field breeding Muscidae. This parasitoid/predator was introduced in California from Jamaica. Adults are voracious predators of house fly eggs and young larvae. Eggs hatch in ca. 4 days and larvae search actively through the substrate for fly pupae, the parasitoid-susceptible stage. Pupae are entered through a hole gnawed in the puparium wall by the young larvae; the hole is closed with what seems to be fecal matrial. The three larval instars are ectoparasitic on the fly pupae within the puparium. Mature larvae emerge into the substrate where pupation occurs. Larval development requires 6-7 days, the pupal development another 14-16 days at 23.9°C. The total life cycle at this temperature is ca. 25 days from egg to adult.
Also please see separate Staphylinidae section.