Distinguishing Immatures of Insect Associates of Southern Pine Bark Beetles

Southern Pine Beetle Handbook

United States Department of Agriculture Forest Service, Cooperative State Research Service, Southern Pine Beetle Handbook, Agriculture Handbook No. 641. October 1985.

Coleoptera

Histeridae

Considerable variation in size exists among the several species of histeridae found associated with pine bark beetles. Generally, however, larvae appear somewhat homogenous in form (fig. 4), with the head two-thirds as long as the thorax. Antennae are three-segmented, mandibles large and curved, each with one large median tooth (some species have a small second tooth) (fig. 5). Maxillae and labium project anteriorly, with four-and three-segmented palps, respectively (fig. 5). The abdomen has nine apparent segments, with the ninth bearing elongate cerci (fig. 6). Each cercus comprises two segments, with stout hairs on each segment.

Figure 4 - Histeridae:
typical larva

Pupae are white and mummy-like and are found in frass material of bark beetles. The larvae do not construct pupal cells.


Figure 5 - Histeridae: dorsal head capsule with mandibular tooth (arrow a) and labial and maxillary palps (arrows b, c)	Figure 6 - Histeridae: two- segmented cercus with hairs

Staphylinidae

Several species of staphylinidae that co-inhabit bark beetles galleries are scavengers and others, as noted by Moser et. al. (1971), are underscribed and their biological roles are undetermined. The large Nudobius luridipennis is, however, predaceous. Goyer et. al. (1980) previously referred to this insect as Leptacinus paurumpunctatus (Gyllenhal). The larva of Nudobius has a protracted head and a ring-shaped collar posteriorly, adjoining the prothorax. The mandibles are long and sickle-shaped and bear no teeth (fig. 7).

Additionally, the maxillae and labium are small, and are masked when viewed from above by an irregularly toothed, fused clypeus and labrum.

	These features separate the staphylinids in general from the histerids described above. Two-segmented cerci are present on the ninth abdominal segment as in the histerids. The pupa (fig. 8) is distinguished by a large truncate anterior, with the head and thoracic portions compressed.
Firure 7 - Nudubius luridipennis: dorsal head capsule with toothless mandibles	Figure 8 - Nudobius luridipennis: pupa with truncate anterior

Trogositidae

The most commonly encountered trogositid (formerly Ostomidae) is the large Temnochila virescens although other species of this family occur in bark beetle-infested trees. Knowledge of the immature habits is confined to T. virescens. The larva (fig. 9) is distinguished by having a well-developed, forward–projecting head about as wide as it is long, with heavily sclerotized mandibles. The head possesses a distinct V-shaped (epicranial) suture dorsally (fig. 10a), with the frons separated into halves. The mesothorax (fig. 10a) possesses two dorsal plates which fuse to form one continuous plate in the later instars. The metathorax retains two distinct dorsal plates in all instars. Length varies from 2.5 mm at eclosion to nearly 20 mm at maturity. The cerci at the end of the abdomen are heavily sclerotized and consist of one segment directed upwards with several scattered long setae.

Figure 9 - Temnochila virescens: larva

Figure 10a - Temnochila virescens: head and
thorax, note fused mesothoracic plates (arrows)
Figure 10b - Thanasimus dubius: head and thorax;
note two distinct plates on mesothorax (arrow)

Cleridae

Thanasimus dubius larvae (fig. 11) are similar in most respects to T. virescens described above. They differ in that the mesothoracic dorsal plates remain separate as two distinct sclerites (fig. 10b). Also, the later in-stars have a pink or purple body color. The thoracic legs are five-segmented. Prepupae and pupae are found in white-lined cells (fig. 12) in the outer bark in which they complete development to the adult stage. The pink pupae typically are exarate, or mummy-like, with curved anal cerci present.


Figure 11 - Thanasimus dubius: third instar larva	Figure 12 - Thanasimus dubius: prepupa in characteristic cell in outer bark (note color)

Colydiidae

Aulonium spp. are the most frequently encountered colydiids associated with bark beetles. The mandibles are of the grinding type, with two distinct teeth and several tiny teeth. Larvae, when viewed dorsally, are slightly larger in diameter in the fifth and sixth abdominal segments. Most characteristically, however, these larvae have a greatly enlarged ninth abdominal segment (fig. 13). Also present on this wartlike ninth abdominal segment are two rigid, curved cerci, usually with a saclike depression between. The head of the pupa is concealed beneath the prothorax, the latter having four tubercles (bumps) on the anterior margin as in the adult. The end of the abdomen retains two strongly curved, chitinous cerci.

Figure 13 - Aulonium sp.: larva with
enlarged ninth abdominal segment

Cucujidae

Wide diversity in form exists among the cucujid larvae. Generally, however, all are dorso-ventrally flattened. The head, bearing a pair of three-segmented antennae, is directed forward (fig. 14). The thoracic segments appear square to rectangular in shape, with the integument being reddish in color in some species. Anal cerci are variable in shape throughout the family with tiny pseudocerci being present on the eighth and/or ninth tergites in some species. We found Silvanus bidentatus to be the most common cucujid adult reared from beetle-infested logs.

Figure 14 - Cucujidae:
early instar larva

Tenebrionidae

The larvae of Corticeus glaber and C. parallelus are readily distinguished from other insect associates by the alternating dark- and light- colored bands on the dorsum of each segment (fig. 15). Bands are less distinct on first-instar larvae. Each segment also possesses one long seta on each lateral margin as well as several shorter setae. The three-segmented antennae are prominent and peglike in appearance. The larvae of C. glaber are indistinguishable from those of C. parallelus but, based on adult emergence, the latter are rarely encountered except in spring and early to midsummer.

Figure 15 - Corticeus sp.:
fifth instar larva

Curculionidae

Weevil larvae most commonly found in association with bark beetle- infested wood are those of the deodar weevil, Pissodes nemorensis (fig. 16). Small larvae of this weevil appear similar to bark beetle larvae. They usually cannot be distinguished by anatomical differences, but they differ in feeding or gallery patterns. Deodar weevil larval galleries meander for considerable distance through the outer sapwood and gradually enlarge as the larvae grow.The galleries terminate in a cell of shredded wood fiber or chip cocoon. Deodar weevil larvae attain lengths of 10 mm or more at maturity, and this large size can be used to distinguish them from most scolytid beetles. The typical exarate pupa (fig. 17) is found in the chip cocoon in the outer sapwood. The long snout on the front of the head distinguishes the weevils from other insects constructing cells or cocoons in frass and woodchips. Adult weevils of the genus Cossonus are found commonly under the bark of trees during the very late stages of bark beetle development (see Goyer et al. 1980). Their larvae, however, are rarely encountered due to this temporal exclusion. They do not construct galleries in the phloem, and thus should not be confused with scolytid immatures having a similar body appearance.
	Figure 16 - Pissodes nemorensis: final instar larva

	Figure 17 - Pissodes nemorensis: pupa in chip cocoon

Scolytidae

A wide variety of primary and secondary scolytid beetles is present in dead and dying pines. The traditional legless grublike larvae appear similar in shape and often in size (fig. 18). Scolytid species are differentiated, classically, by their discrete gallery patterns etched in the phloem and outer sapwood. It is not the purpose here to provide the minute details of larval characteristics encompassing the many species of larvae potentially present. A vast array of literature is available in this area (see Peterson 1951 for some of these).
	Figure 18 - Scolytidae: typical bark beetle larva
The larvae of the black turpentine beetle (Dendroctonus terebrans) can, however, be distinguished from most other coinhabitants of pine phloem by the presence of darkened, well-developed anal cerci (fig. 19) lacking or inconspicuous in other species.

Pupae of Ips spp. and a few other scolytids are recognized in profile by the retracted head not visible from above (fig. 20). Additionally, the spines on the posterior lateral margins of the elytra further differentiate Ips spp. from other pupae, e.g., the southern pine beetle.


Figure 19 - Dendroctonus terebrans: final instar larva with dorsal cerci visible in bottom specimen	Figure 20 - Ips sp.: lateral view of pupa. Note head not visible from above

Cerambycidae and Buprestidae

The round- and flatheaded wood borers are usually easily distinguished by their large size, especially in the later larval instars. Both families are represented in southern pines by tapered legless grubs.

They differ from scolytid bark beetles by being elongate rather than C-shaped. Cerambycid larvae (fig. 21) taper less abruptly from front to rear than do buprestid larvae (fig. 22. Also, the cerambycids do not possess and inverted "v" on the large first thoracic segment as do buprestid larvae (fig. 22). Monochamus spp. and Neacanthocinus obsoletus are the cerambycid borers most frequently encountered. Pupae found in cells hollowed out of the shredded (cerambycids) or powdered (buprestids) frass are distinguished by their resemblance to the adults, with cerambycids (fig. 23) possessing long, coiled antennae.

Figure 21 - Cerambycidae: larva


Figure 22 - Buprestidae: larva with inverted "V" on first thoracic segment	Figure 23 - Cerambycidae: pupa with coiled antennae

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