Myrmosicarius exrobusta Brown

Brown, Brian V., Braganca, Marcos A. L., Gomes, Diego S., Queiros, Jarbas M. & Teixeira, Marcos C., 2012, Parasitoid phorid flies (Diptera: Phoridae) from the threatened leafcutter ant Atta robusta Borgmeier (Hymenoptera: Formicidae), Zootaxa 3385, pp. 33-38 : 36-37

Myrmosicarius exrobusta Brown new species

Fig. 3 .

Diagnosis. This species is part of a group that have 3 notopleural setae present, differing by the shape of the apex of the oviscape. In the latest identification key to species of this genus ( Disney et al., 2006), this new species keys to couplet 3, where the apices of the oviscape of M. grandicornis Borgmeier and M. brandaoi Disney et al. are compared. The oviscape of M. exrobusta is much less rounded than that of M. grandicornis , and less sinuous and differently shaped than that of M. brandaoi .

Description. Female. Body length 1.5–2.0 mm. Body color brown. Frons with 4-4-4 short frontal setae; ventral interfrontal setae arise nearer to eye margin than midline, strongly medioclinate. Flagellomere 1 rounded-oval, laterally flattened. Palpus extremely short, brown, proboscis long, narrow; labella twice as long as labrum. Thorax with three notopleural setae. Legs with fore- and midtarsomere 5 elongate, narrowed, with claws reduced. Tarsomere 5 of hind leg not apically narrowed. Hind tibia with single dorsal setal palisade and posterodorsal row of small setae, most apical seta much larger. Costa 0.30–0.35 wing length. Vein R2+3 present. Halter brown. Posterior margin of abdominal tergites with minute setae only. Oviscape only slightly sinuous, with bluntly rounded apex.

Etymology. Named for being “from” (ex -) the host ant species.

Holotype. Ƥ, BRAZIL: Rio de Janeiro, 23°01’S, 43°28’W), 10.i.2010, D. da Silva Gomes [barcode: LACM ENT 305112] (MZSP).

Paratypes. 2 Ƥ, same data as holotype (LACM, MZSP).

Natural history. The attack behavior of the two species of Eibesfeldtphora described herein consisted of an approach from the rear or from the sides of A. robusta workers and a landing on the hind part of their heads where, apparently, the phorid flies introduced their ovipositors. This behavior is similar to that of E. tonhascai (Brown) and E. elongata (Brown) females against the A. sexdens host ( Bragança et al., 2008; Bragança et al., 2009) and E. curvinervis (Malloch) on A. cephalotes (L.) ( Feener & Brown, 1993), but differs from that of E. erthali (Brown) and E. bragancai (Brown) , which introduce their ovipositors into the gaster of A. laevigata and A. bisphaerica workers, respectively ( Bragança et al., 2003; Bragança et al., 2002). The anti-parasitoid defense behavior of A. robusta against Eibesfeldtphora species was similar to that observed in A. sexdens against E. tonhascai and E. elongata ( Bragança et al., 2008; Bragança et al., 2009): the workers ran towards the nest entrance holes, attacked the parasitoid with their mandibles or lowered their bodies and protected the head with their legs to avoid the fly’s approach. The larval development of the new species of Eibesfeldtphora probably occurs inside the cephalic capsule of A. robusta , with a single puparium forming between the host’s mandibles after its death and from which the adult parasitoid emerges, as observed for other Eibesfeldtphora species which attack Atta spp. ( Bragança et al., 2008; Bragança et al., 2009). This sequence also occurs even when oviposition is in the gaster ( Bragança et al., 2003; Bragança et al., 2002). Females of Myrmosicarius exrobusta also pursue A. robusta workers, approaching from behind to attack, but under field conditions it was impossible to verify exactly where this species oviposits in the host’s body, due to the parasitoid’s speed of attack and also to its small size. The defense behavior of A. robusta against this species was to run to the nest and attack the parasitoid with its mandibles.

It was also common to observe worker minims on plant fragments that were being transported to the nest. One of the functions of this behavior, called “hitchhiking”, seems to be as a defense strategy of Atta against parasitoid activity ( Feener & Moss, 1990, Linksvayer et al., 2002, Vieira-Neto et al., 2006). Whether the presence of these minims served to protect A. robusta against phorid parasitoids could not be verified during the present study.

In Rio de Janeiro, the phorids were found attacking A. robusta workers both on the trails and at the nest entrance holes, in contrast to other species which choose specific places to attack their host ( Bragança et al., 2003). However, 85% of Myrmosicarius sp. individuals were collected from open areas whereas 96% of Eibesfeldtphora specimens were captured from closed areas. Elizalde and Folgarait (2010) discovered associations between phorid species and specific habitats due to the special climatic conditions generated for each one, including humidity and light intensity.

Just as A. robusta may be threatened with extinction, due to destruction of its habitat in the coastal areas of Espírito Santo and Rio de Janeiro states, this concern may also be extended to its parasitoid phorids. These flies appear to specifically parasitize A. robusta , as do the phorids E. erthali and E. bragancai that specifically attack the ants A. laevigata and A. bisphaerica , respectively ( Bragança et al., 2003; Bragança et al., 2002). Additionally, these phorids would not have alternative hosts if A. robusta became extinct, since no other Atta species were observed in the restinga vegetation.

Therefore, it seems certain that the three species of phorid parasitoids of A. robusta will also disappear if their host becomes extinct. This justifies the inclusion of these flies in the list of the Red Book of Endangered Brazilian Wildlife ( Machado et al., 2008). In order to increase our knowledge of these parasitoids, and also the chances of conserving them, we recommend basic biological studies on their biology be made to collect information on larval development, pupal formation, and adult fly emergence.

Figures

FIGURES 1 – 3. Female phorid fly oviscapes, lateral. 1. Eibesfeldtphora breviloba; 2. Eibesfeldtphora digitalis; 3. Myrmosicarius exrobustus.