Pheidole proxima Mayr

Sarnat, Eli M., Fischer, Georg, Guenard, Benoit & Economo, Evan P., 2015, Introduced Pheidole of the world: taxonomy, biology and distribution, ZooKeys 543, pp. 1-109 : 46

Taxon classification Animalia Hymenoptera Formicidae

Pheidole proxima Mayr Fig. 84, 88L

Pheidole proxima . Pheidole proxima Mayr 1876: 104 (s.w.) AUSTRALIA, Peak Downs, Queensland [NHMW, examined]. Current subspecies: nominal plus bombalensis , transversa .

Diagnosis among introduced Pheidole .

Reddish brown. MajorHW 0.95-1.05, HL 1.04-1.21, SL 0.44-0.50, CI 87-92, SI 42-52 (n=4). Head subquadrate (Fig. 7). Posterolateral lobes lacking sculpture (including foveolate ground sculpture, carinae and rugae) posterior to maximum extent of antennal scapes in repose (Fig. 9). Head glossy, lacking foveolate ground sculpture. Hypostomal bridge with a small median tooth in addition to a pair of larger inner teeth (Fig. 18). Promesonotum in profile forming a single dome (Fig. 4), lacking a distinct mound or prominence on the posterior slope. Promesonotal dorsum glossy, lacking foveolate ground sculpture or striae. Pronotal striae in dorsal view mostly absent (Fig. 23). Metapleuron with moderate rugulae and some weak punctation (Fig. 16). Petiolar node strongly punctate (Fig. 16). Postpetiole not swollen relative to petiole (Fig. 3). MinorHW 0.46, HL 0.52, SL 0.40, CI 90, SI 86 (n=1). Head predominantly glossy (Fig. 36), lacking punctation and or rugae above eye level. Posterior head margin weakly convex (Fig. 45) to weakly concave (Fig. 46) in full-face view. Antennal scapes reach but do not surpass posterior head margin (Fig. 41). Mesopleuron entirely punctate (Fig. 52a). Promesonotum in profile forming a single dome (Fig. 42), lacking a distinct mound or prominence on the posterior slope. Propodeal spines moderately produced and spiniform (Fig. 52b). Petiole distinctly sculptured except for apical portion of node. Postpetiole not swollen relative to petiole (Fig. 3).

Identification, taxonomy and systematics.

Pheidole proxima is a relatively small, brownish yellow, short-limbed species with a strongly shining integument. The phylogenetic placement of Pheidole proxima is unknown, but it almost certainly clusters within an Old World clade that has radiated across Australia and New Guinea. The species is slightly smaller than Pheidole megacephala , but both have workers with almost entirely glossy faces. The postpetiole of Pheidole proxima is not swollen relative to the petiole (Fig. 3), as it is in Pheidole megacephala (Fig. 1). The head of the major is subquadrate (Fig. 7), while that of Pheidole megacephala is more heart-shaped (Fig. 6). The antennal scapes of the minor do not surpass the posterior head margin (Fig. 41), as they do in Pheidole megacephala (Fig. 40). The other two Pheidole species established in New Zealand are Pheidole rugosula and Pheidole vigilans . The glossy face of Pheidole proxima easily separates both worker castes of from those of Pheidole rugosula . In addition to being significantly smaller (major HW <1.0 mm, minor HW <0.48 mm) than Pheidole vigilans (major HW> 1.2 mm, minor HW> 0.52 mm), the major of Pheidole proxima is more sculptured (Fig. 16 vs. Fig. 17), and the hypostomal bridge has a distinct median tooth (Fig. 18 vs. Fig. 19). The minors of Pheidole proxima are separated from those of Pheidole vigilans by the shorter scapes (Fig. 41 vs. Fig. 40), more sculptured mesopleuron (Fig. 52a vs. Fig. 51a), and more robust propodeal spines (Fig. 52b vs. Fig. 51b). Additional taxonomy of these species is discussed in ( Berry et al. 1997).

Comparison of the Pheidole proxima Mayr type series and images of the two subspecies suggests that all three taxa are heterospecific. There is some reason to believe, however, that the name Pheidole proxima Mayr does not apply perfectly to the species recently introduced to New Zealand. The specimens examined from New Zealand conflict with Mayr’s original description and type specimens on several points. The pronotal dorsum of the type major worker is transversely rugose whereas that of the New Zealand specimens are completely glossy. Although we were unable to examine minors from the type series, Mayr described the head of the minor worker as coriaceous and striate-rugose with scapes that barely exceed the posterior margin. In contrast the minor workers from New Zealand have heads that are completely glossy and scapes that do not exceed the posterior head margin. Forel, in his description of Pheidole proxima subsp. bombalenis, describes the minor worker as identical to Pheidole proxima Mayr with the exception of having longer propodeal spines. The specimen images of the Pheidole bombalensis syntype minor show a strongly sculptured face, similar to the pattern described by Mayr. The major workers from the type series are larger than the New Zealand specimen we measured (HW 1.03-1.05 mm vs.HW 0.95 mm), have relatively narrower heads (CI 87-89 vs.CI 92), and relatively shorter antennal scapes (SI 42-46 vs.SI 52). While a more exhaustive survey of Australia’s Pheidole may reveal the New Zealand population to be more closely related to another species from that fauna, we follow Berry et al. (1997) in using Pheidole proxima Mayr.

Biology.

The only natural history published for Pheidole proxima was recorded by Green and Gunawardana (2006) from their work with the New Zealand incursion. They reported that Pheidole proxima produced large nests recognizable by tiny conical mounds of sandy or grainy material above the ground near the entrance. The size of the mounds varies with soil type, with mounds as small as 5 mm high by 200-300 mm in diameter. They are tolerant to disturbance and capable of invading structures. The minor and major workers are both active foragers and were observed recruiting to both sweet and savory baits in high numbers.

Distribution.

Pheidole proxima Mayr is native to Queensland, Australia. The sparse records of the species are scattered from Cape York at the northernmost tip of the continent down to the Gold Coast. The species is introduced to New Zealand and was first detected during a 2004 survey of the Port of Napier following an incursion of Solenopsis invicta ( Green and Gunawardana 2006). The species is now widespread across the North Island from the Napier-Hastings area to Auckland.

Risk statement.

Pheidole proxima is at most considered a nuisance species in New Zealand on account of its ability to infest structures. However, very little is known about the species, including its impact on agricultural systems and native ecosystems. There is little reason to believe that it will become globally or regionally widespread.