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.

Diptera

Cecidomyiidae

These larvae (fig. 24) are small, cylindrical, usually less than 5 mm in length, and are sometimes white, or more often, various shades of yellow, orange, or red. They possess a retracted head capsule that is very small, lightly sclerotized, with indistinctly differentiated mouth parts, two to three segmented antennae, and a pair of cephalic bars projecting posteriorly from the lateral margins. The prothorax of mature larvae has a sternal spatula, or "breast bone", visible ventrally.

Figure 24 - Cecidomyiidae: larvae

Larvae possess three thoracic segments and eight abdominal segments plus a small cephalic segment between the prothorax and head capsule plus a terminal anal segment (division). Many species are capable of "jumping" to considerable heights when disturbed.

Sciaridae

Sciarid larvae are small, cylindrical, 5-12 mm in length, with an opaque body (fig. 26). The well-developed head is usually deeply pigmented and may appear triangular in outline when viewed from above. Within the head capsule, the posterior tentorial bridge is complete or nearly complete. Mandibles and maxillae, both of which have a series of teeth on their edges, are darkly sclerotized and compressed. The prothorax and first seven abdominal segments each have a pair of spiracles. "Creeping welts", or transverse ridges, are present on the ventral side of the abdomen.

Figure 26 - Sciaridae:
pigmented larva

Dolichopodidae

Dolichopodid larvae, as typified by Medetera spp. (fig. 27), are slender, cylindrical, slightly tapered anteriorly, 5-10 mm in length, and white in color. The head segment usually is short and is unsclerotized externally. The head skeleton is completely retracted in the thorax and is highly modified. Characteristically, this skeleton possesses metacephalic rods that are expanded apically. The body is smooth with a delicate integument. The posterior end possesses two spiracles and the surface of the terminal segment is crossed with a vertical and horizontal furrow resulting in a four-lobed appearance. This latter character is most useful in separating Medetera larvae from other Diptera. The pupa (fig. 28) is exarate and creamy white except for sclerotized areas. The last of eight abdominal dorsal sclerites bears a crest of large, sometimes hooked, hairs or spines.


Figure 27 - Medetera sp.: larve with lobed terminal segment	Figure 28 - Medetera sp.: pupa with hooked dorsal hairs

Stratiomyiidae

Zabrachia polita larvae are elongated, flattened, and are readily distinguished by the presence of flexible plates or "arms" on each segment (fig. 29). The head capsule is well developed, but is retracted more than half its length into the thorax.

Figure 29 - Zabrachia polita:
larva with flexible "arms"

Lonchaeidae

Lonchaea sp. larvae (fig. 30) are slender, cylindrical, and taper anteriorly from about the first or second abdominal segment. Larvae are 10 mm or less in length and are whitish to creamy yellow in color. The head is reduced to an internal skeleton with simple mouthhooks. The 11-segmented body is smooth and shiny except for ventral "creeping welts" possessing several transverse rows of spines on each abdominal segment. The prothorax has a pair of fan-shaped spiracles. The posterior end is blunt with spiracles situated on short, distinctly sclerotized elevations. The pupa (fig. 31) is typically coarctate, or "bulletlike" and is reddish brown with an average length of 5.2 mm.


Figure 30 - Lonchaea sp.: larva with ventral spines or "creeping welts"	Figure 31 - Lonchaea sp.: coarctate pupa

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