Monomorium ergatogyna

A southwestern U.S. species with unusually long-lived Monomorium queens.

Identification
DuBois (1986) - A member of the Monomorium minimum species group. Queen: Wingless; head (excluding lateral margin of clypeus) lacking nonpiliferous punctures and rugae; alitrunk with more than 30 erect to suberect setae projecting above dorsal outline; mesopleuron punctate, PI 35-44 (38).

It is possible that queens of this species might be confused with queens of Monomorium cyaneum or Monomorium wheelerorum. Monomorium ergatogyna queens can be separated from those of M. cyaneum by the fringe of setae on the antennal scape and the reduced head sculpturing in M. ergatogyna.

Distribution
Known from locally abundant populations occurring along Pacific coastal California, inland California sites in southern California, Nevada and Utah.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Biology
DuBois (1986) - Recorded as nesting under stones (Brues, 1903), in soil or in rotten wood (Essig, 1926). Mallis (1941) records this species (misidentified as Monomorium minimum) nesting in a dry, unshaded area (in the Berkeley Hills) with tumuli forming tiny craters (2-4 cm in diameter). Further details of nest architecture are unknown. In addition to the variety of nesting sites occupied by M. ergatogyna, it has a wide altitudinal tolerance, from 9 m (Long Beach) through 1500 m (H James Reserve).

Monomorium ergatogyna queens have the longest recorded life span in this genus. Colonies (collected in the field) have been maintained in the laboratory for over two years with the original queens (pers. observ.). This compares with an average queen longevity of 39 weeks for Monomorium pharaonis (Peacock and Baxter, 1950) and 8 months to 1 year for M. minimum (pers. observ.). Monomorium ergatogyna worker longevity varies from 4-8 months (4 months appears to be the usual life span for workers of this genus). There appear to be three larval instars. Colonies of M. ergatogyna have multiple, functioning queens (2-6) (pers. observ.).

Sexual forms emerge during July and August {collections of reproductives: Santa Barbara Island, 12 June 1978 (gyne larvae); Santa Cruz Island, 23 July 1963 (1 male); East Anacapa Island, 23 August 1978 (10 males and 20 unmated queens)}. Only 2 males have been collected from the mainland {Pasadena, 17 April 1929}. If this date is correct, M. ergatogyna may produce sexuals twice a year. Another possibility is that an undescribed species occurs sympatrically with M. ergatogyna; no morphological differences have been found to support this theory.

Brues (1903) reported a species of Microdon (Diptera: Syrphidae) from a nest at Pacific Grove. No other symbionts have been reported.

It appears that the Argentine Ant, Linepithema humile (Mayr), occupies much of the habitat once utilized by M. ergatogyna (pers. observ.).

Determination Clarifications
DuBois (1986) - A great deal of confusion in previous literature has resulted from the erroneous assumption that M. minimum and  Monomorium viridum peninsulatum occurred in California. Furthermore, M. ergatogyna was thought to inhabit only the coastal islands (Essig, 1926; Mallis, 1941; Cook, 1953). Although the San Francisco and Los Angeles populations of this species currently appear allopatric, much more collecting must be done before this point can be decided. Additionally, there appear to be some minor size differences between queens from island localities versus those from the mainland. It seems best to regard all this material as M. ergatogyna.

Nomenclature

 *  ergatogyna. Monomorium minutum subsp. ergatogyna Wheeler, W.M. 1904d: 269 (w.q.) U.S.A. DuBois, 1986: 88 (m.). Subspecies of minimum: Wheeler, W.M. 1914b: 42. Raised to species: Essig, 1926: 857. Junior synonym of minimum: Creighton, 1950a: 219. Revived from synonymy, status as species: DuBois, 1986: 86. Senior synonym of wheelerorum: Ward, 2005: 14.
 * wheelerorum. Monomorium wheelerorum DuBois, 1986: 91, figs. 11, 17, 80, 81-86 (w.q.) U.S.A. Junior synonym of ergatogyna: Ward, 2005: 14.

Worker
Head: (representing separate localities; N= 10) HL 0.40-0.60 (0.49), HW 0.33-0.42 (0.39), SL 0.31-0.40 (0.35), EL 0.06-0.10 (0.07), MOD 0.04-0.06 (0.05). Structure—CI 70-91 (79), SIL 62-85 (71), SIW 79-98 (89). In full frontal view, side straight. Scape reaching or surpassing occiput by less than length of pedicel. Alitrunk. PW 0.20-0.28 (0.25), PL 0.18-0.24 (0.20), WL 0.48-0.59 (0.52). Structure—Propodeum rounded; declivitous face half length of basal face. PI 35-44 (38). Pilosity—Dorsal surface of alitrunk with 18-25 erect to suberect setae. Sculpture—Anterior propodeal suture with moderate, longitudinal rugae. Petiole. Dorsum of node convex. Postpetiole. Anterior subpostpetiolar process of moderate size, located medially on venter. Setae erect on dorsum of node and on venter (beneath node), erect to suberect on sides, remainder bare. Posterior edge of postpetiole with dense, non-piliferous punctures. Color: Base of mandible, lateral margin of clypeus, and antenna yellow brown.

Queen
As described for Monomorium cyaneum except as indicated. Head. (representing different localities; N= 10). HL 0.59-0.71 (0.67), HW 0.55-0.65 (0.61), SL 0.41-0.52 (0.47), IOD 0.12-0.18 (0.17), OD 0.04-0.05 (0.05), EL 0.12-0.15 (0.14), MOD 0.09-0.11 (0.10). Structure—CI 79—95 (90), SIL 58-77 (70), SIW 63-91 (77). Side straight to slightly convex. Frontal carinae diverging strongly posteriorly. Pilosity—Setae erect near clypeus, frons, gula, occiput, and ocelli, suberect to decumbent on malar area, appressed on remainder. Setae of scape erect on anterior edge (forming a fringe of setae), decumbent to appressed on remainder, of pedicel and flagellum (except club) suberect to decumbent, of antennal club appressed. Sculpture—Smooth and shining except as follows: moderate, parallel, longitudinal rugae beginning all along lateral margin of clypeus and extending to level of antennal insertion. Small piliferous punctures evenly distributed on head. Alitrunk. PW 0.40-0.48 (0.43), PL 0.21-0.31 (0.28), WL 1.00-1.15 (1.06). Structure—Propodeum evenly rounded (basal and declivitous faces do not meet at an angle). PI 19-28 (26). Pilosity—As in Monomorium minimum. Sculpture—Large piliferous punctures on dorsum of scutum, smaller piliferous punctures on dorsum of scutellum, propodeum and side of alitrunk. Several moderate to large semicircular rugae anterior to propodeal spiracle. Petiole: Dorsum of node convex. Setae decumbent to appressed on anterior surface of node, erect on dorsum and side of node, and absent from posterior surface of node. Posterior surface of node with large, transverse, concentric, semicircular rugae which extend over half of side of node. Postpetiole. Dorsum of node convex. Dorsum and sides of node smooth with piliferous punctures. Posterior 1/5 of node with some non-piliferous punctures. Sometimes, lower 2/3 of side of node covered with dense, non-piliferous punctures. Color. Head brown except as follows: antenna, mandible, and lateral margin of clypeus yellow to yellow brown.

Male
Head. Measurements (representing 1 nest; N= 5) HL 0.55-0.58 (0.56), HW 0.66-0.71 (0.69), SL 0.29-0.35 (0.31), IOD 0.18—0.20 (0.19), OD 0.06 (0.06), EL 0.24-0.26 (0.25), MOD 0.12-0.16 (0.15). Structure—CI 114-127 (123), SIL 53-60 (55), SIW 41-53 (45). Sculpture—Large, concentric, transverse rugae occurring on posterior 1/3 of head. Large rugae beginning all along lateral margin of clypeus, continuing behind antennal insertion and converging with frontal carina. Occasionally, several moderate rugae may converge on anterior ocellus. Alitrunk: Measurements PW 0.49-0.56 (0.51), PL 0.38-0.42 (0.40), WL 1.28-1.29 (1.29). Structure—Pronotal-scutal suture located medially on alitrunk. Propodeum angular, basal and declivitous faces of approximately equal length. PI 29-33 (31). Wings present; 5-7 hamuli on hindwing. Pilosity—As in M. minimum. Sculpture—Anterior edge of mesopleuron, near procoxa, with series of small transverse rugae. Petiole. Dorsum of node convex. Setae subdecumbent to appressed on anterior surface of node, suberect to erect on dorsum, absent from posterior surface of node. Side of petiole with small non-piliferous punctures; dorsum smooth and shining with a few piliferous punctures. Postpetiole: Dorsum of node convex. Anterior subpostpetiolar process of moderate size, located medially on venter. Setae erect to suberect on dorsum and/or posterior surface of node; absent elsewhere. Dorsum of node smooth, remaining surfaces with dense non-piliferous punctures. Genitalia. Ninth sternite with 7-10 erect setae. Aedeagus with 13 teeth. Cuspis of volsella with 3 setae.

Type Material
DuBois (1986) - Syntypic series consists of “numerous workers and eight females taken from three different nests” (Wheeler, 1904). California: Los Angeles Ca, Catalina Island, Baker; (16 queens, 21 workers; ), (17 queens, 12 workers; ). Lectotype queen selected from AMNH series bears red, handwritten label: Monomorium ergatogyna Wheeler Lectotype M. DuBois 1980.