George C. Wheeler and Jeanette Wheeler.
Young larvae of Veromessor pergandei (Hymenoptera: Formicidae).
Psyche 94:303-308, 1987.

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YOUNG LARVAE OF VEROMESSOR PERGANDEI
(HYMENOPTERA: FORMICIDAE: MYRMICINAE)
Research Associates, Florida Department of Agriculture* Time was when it seemed every myrmecologist wanted to work on Veromessorpergandei, but we can find no mention of it in the last eight years of Zoological Record. When we lived with it in Death Valley and southern Nevada it became one of our favorite ants. To differentiate instars we would like the following specimens: a first instar inside an egg; a second instar inside a first instar that is ready to moult; a third instar inside a second ready to moult; etc.; a mature larva; a prepupa. Fortunately our V. pergandei material meets all the requirements, except the first. V. pergandei is poly- morphic, which presents another problem: when does subcaste dif- ferentiation begin? How can one tell whether a small larva is the young of a major or a mature of a minim; or whether a medium- sized larva is the mature of an intermediate worker or the half- grown larva of a major? In V. pergandei subcaste differences apparently begin in the fourth instar and are manifested only in size. V. pergandei presents another problem: there are two body shapes for mature worker larvae. We have no explanation for this. Vermessor pergandei (Mayr)
Figures 1-6.
Egg.
Figure 1. About 0.32 X 0.52 mm.
First Instar. Figure 2. Length (through spiracles) about 0.48 mm. Entire larva feebly sclerotized. Body sac-like; head on anterior end and greater in diameter then thoracic somites. Spiracles about 0.006 mm in diameter. No spinules nor hairs on body. Cranium subcircular in anterior view. Antennae represented by 2 sensilla. About 20 head hairs, 0.013-0.025 mm long, unbranched. Mouth parts small. Labrum with a ventrolateral swelling on each half of anterior surface; 2 or 3 sensilla on each half of ventral surface. Mandibles subtriangular; apical tooth straight and sharp-pointed; *Mailing address: 3358 NE 58th Avenue, Silver Springs, Florida 32688 Manuscript received by the editor June 4, 1987



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304 Psyche [vo~. 94
Figures 1-5.
Left mandible in anterior view, Xl85; larva in side view and egg, Xl9; head in anterior view, X76.
1. Egg.
2. First Instar. 2a, Mandible; 2b,
profile; 2c, head.
3. Second Instar. 3a, Mandible; 3b, profile; 3c, head. 4. Third
instar. 4a, Mandible; 4b, profile; 4c, head. 5. Fourth Instar. 5a, Mandible; 5b,
profiles of two sizes of larvae; 5c, head. medial border with a small projection. Maxillary palp with 5 sensilla on a slight elevation; galea represented by 2 sensilla. Labium short and wide; palp represented by 5 (?) sensilla. Second Instar.
Figure 3. Length (through spiracles) about 1.6 mm. Dorsal profile of body feebly C-shaped, ventral feebly sigmoid; T 1 -T3 nearly same diameter; AIII-AIV widest, tapering slightly to anterior end and more rapidly to posterior end; head and anus ventral; anus with a small posterior lip. Spiracle diameter about 0.008 mm. Integument with minute spinules in short rows on venter of thorax and all surfaces of AVIII-AX. Body hairs on Tl only; 0.006-0.018 mm long, slightly curved and with frayed tip. Cranium oval, narrowed ventrally; length subequal to width. Antennae with 3 sensilla each. Head hairs few (about 35); 0.006-0.018 mm long, with



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19871 Wheeler & Wheeler-Larvae of Veromewr 305 short frayed tip. Labrum feebly bilobed; anterior surface of each lobe with a few sendla near and on ventral surface. Mandible feebly sclerotized. Maxillary palp represented by a cluster of 5 sensilla; galea a slight elevation with 2 sensilla. Labial palp represented by a cluster of 5 sensilla.
Third Instar.
Figure 4. Length (through spiracles) 2.4-2.8 mm. Similar to second instar except as follows: Body widest at AIII, venter nearly straight; dorsal profile long and C-shaped. Spiracles about 0.019 mrn in diameter. Entire integument with minute spi- nules in short arcuate rows. Body hairs very few; on thorax only; 0.013-0-028 mrn long, with very short-Wid tip. Cranium subhex- agonal in anterior view; width and length subequd. About 30 head hairs; 0.013-0.058 rnm long, with short 2- or 3-branched tip. Labrurn bilobed; each lobe with 2 sensilla on anterior surface; ven- tral surface with 3 sensilla on each half; posterior surface with 3 sensilla near ventral border of each lobe and with a cluster of 3 sensilla near middle; with small patches of isolated spinules dorsally and near middle. Maxilla with round-pointed apex and with a few short rows of minute spinules; palp a short frustum with 5 sensilla; gab a low rounded knob with 2 sensilta. Labium with small patches of spinules dorsally near middle, the spinules isolated or in short rows; palp a slightly elevated cluster of 5 senailla; an isolated sensillurn between each palp and the opening of the sericteries; the latter a short transverse slit. Hypopharynx with a few minute spi; nules in short transverse rows.
Fourth Instar. Figure 5. Length (through spiracles) about 3.0-4.9 mm. Similar to third instar except as follows: Body hairs sparse, generally distributed; 0.0134.1 mm long; with slightly curved shaft and short-frayed tip. About 45 head hairs; 0.012-0.05 mm long. Posterior surface of labrum with rather coarse spinules, isolated or in short rows dorsally. Mandible moderately sclerotized; apical tooth long, narrow and sharp-pointed; subapical tooth short- er and less pointed. Maxillary palp and galea more elevated. Labial palp a low knob with 5 sensilla. Hypopharynx with numerous short transverse rows of minute spinules; upper portion with numerous short ridges [furrows?] converging into pharynx. Fifth Instar (Mature Larva).
Figure 6. Length (through spira-
cles) 4.3-6.8 mm. Similar to fourth instar except as follows: Body profile pogonomyrmecoid but of two different shapes: (1) stout, with All and AIII swollen dorsally; (2) abdomen swollen and sac-



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306 Psyche [vo~. 94
Figures 6-7. Fifth Instar (Mature Larva). 6a (hairs omitted) and 6b, profiles,
Xl9; 6c, left mandible in anterior view, Xl85; 6d, head in anterior view, X76. 7. Profiles of mature larvae to show size range (hairs omitted), X8.7a. Major worker; 7b, minor worker.
like, thorax narrowed abruptly and turned ventrally, Tl about same diameter as head length. Otherwise larvae with different profiles similar. Anus with small lips. Leg, wing and gonopod vestiges pres- ent. Body hairs with bifid or frayed tip. Antennae small, each with 3 sensilla; at midlength of cranium. Head hairs with slightly curved shaft and 2- or 3-branched tip. Mandibles ectatommoid; heavily sclerotized; apical tooth long and narrowed to a sharp point; sub- apical tooth at end of medial blade, with stout base and sharp apex. Maxillary palp paxilliform with 5 (4 apical and 1 lateral) sensilla; galea stout and digitiform with 2 apical sensilla. Labium with mi-



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19871 Wheeler & Wheeler- Larvae of Veromessor 307 nute spinules in short to long arcuate rows which are arranged in subtransverse rows; opening of sericteries a moderately long trans- verse slit.
Material studied: numerous larvae from Death Valley National Monument, California and Boulder City, Nevada. In studying the living larvae the following characters will be most useful in distinguishing instars: First instar. Lacks hairs on body. Head hairs few (about 20). Second Instar. Body hairs very few, confined to Tl only. Head hairs few (about 35). Third Instar. Body hairs very few, some on each thoracic somite. Fourth Instar. Body profile lacks distinct neck. Entire integument covered with spinules and hairs, the hairs with short frayed tips. Fifth Instar (Mature Larva). Body profile pogonomyrmecoid. Length 4.3-6.8 mm. Body hairs with short 2- or 3-branched tip.
The larva of each of five instars of Veromessor pergandei is de- scribed in detail and illustrated. In the fifth instar there are two types of body profiles. The instars of living larvae may be differentiated by a few easily observed characters.




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