Exetasis jujuyensis Gillung

Barneche, Jorge Adrian, Gillung, Jéssica Paula & González, Alda, 2013, Description and host interactions of a new species of Exetasis Walker (Diptera: Acroceridae), with a key to species of the genus, Zootaxa 3664 (4), pp. 525-536 : 529-535

Exetasis jujuyensis Gillung sp. nov.

( Figs. 2 B, 3, 7, 8, 9)

Type material. Holotype female, ARGENTINA: Jujuy: Villa Jardín de Reyes, 20.iii.2008, D. Vieyra col. Number of specimen: 5358/1 – MLPA. The holotype is deposited in the Museo de la Plata, Universidad Nacional de La Plata, La Plata, Argentina (MLPA).

Diagnosis. Large body size (body length: 19.1 mm; wing length: 15.9 mm), light brown, with faint yellow markings in the live specimen (Fig. 9) [which became darker and disappeared in the dried, pinned specimen] ( Fig. 3 ), without black spots, covered by dense, yellow pilosity; antennae as long as the head (see Remarks), with a narrow, elongate flagellum; wing relatively long, extending beyond the tip of abdomen, without markings; abdomen globose.

Description. Female: Head ( Figs. 3 , 9). Antenna as long as the head; scape twice as long as pedicel; pedicel short, cylindrical; flagellum black, cylindrical and narrowed at the apex, bearing numerous terminal setae (see Comments); frons black, small and flattened; ocellar tubercle reduced, quadrangular in shape; two ocelli present; mouthparts very reduced, composed of a tiny proboscis bearing numerous terminal setae. Thorax ( Figs. 3 , 9). Brown, slightly lighter than abdomen, with faint light yellow markings; coxae, femora and tarsus light brown; tibiae dark brown; calypter dark brown, with margins even darker. Wing ( Fig. 2 B). Wing membrane light brown, without markings; microtrichia present only on costal cell; subcosta ending beyond the middle of the wing; R2+3 slightly curved at the apex; R4+5 reaching wing margin; M1 and M2 ending before wing margin; M3 fused to CuA1 both basally and distally of cell m3; CuA2 fused with A1 before wing margin; A2 very short. Abdomen ( Figs. 3 , 9). Globose; tergites light brown; sternites dark brown. Terminalia . Tergites VII and VIII with the same form as tergite VI, but smaller; tergite IX semicircular, with posterior margin black, thickened, bearing numerous black hairs; sternites VI and VII square; sternite VIII square, with posterior margin trilobate, presenting numerous black spines; hypoproct barely visible, almost fused with cerci; cerci yellow, with numerous yellow hairs.

Remarks. Both the antennae are broken off in the pinned specimen so they are not shown in Fig. 3 . They were then placed in a microvial on the pin with the specimen.

Etymology. The species is named Exetasis jujuyensis in reference to the province Jujuy, where the spider was collected.

Comments. This Argentinean species is the only non-Brazilian representative of the genus and can be readily differentiated from all other Exetasis species based on the large body size, light brown body coloration with faint yellow markings and narrow, elongate flagellum. Exetasis jujuyensis Gillung sp. nov. is closely related to E. calida , sharing the fusion of veins M3 and CuA1 both basally and distally of cell m3. Only the female is known.

Biological data. After being kept in the laboratory for approximately eight months, the spider began to weave a "silk bed" in a depression made in the substrate for molting. Although it adopted the belly up normal position of molting (Baerg 1958) it did not complete the molting process. The spider died 11 hours later and an acrocerid larva of five millimeters in diameter emerged through a hole made ??in the ventral part of the abdomen ( Figs. 4 , 5 ). Before emergence, the parasite ate most of the soft parts of the spider, causing its death. The larva then began to move and left a slime trail while heading up to reach the tree trunk that served as the spider’s refuge ( Fig. 6 ). Only a single larva emerged from the spider host.

The recently emerged larva ( Fig. 6 , 7 ) presented a pair of dark brown (almost black) spiracles ( Fig. 7 B, C). Eleven days after emergence, the larva developed a cephalic zone, a globose portion that would later turn into the adult head ( Fig. 7 C). Seventeen days post-emergence, the larva reached the pupal stage, with clearly developed head and eyes, thorax with retracted legs and wings of half the adult size also retracted on the venter of the thorax ( Fig. 8 ). Finally, after 34 days the female adult emerged (Fig. 9).

Discussion

According to some authors, spiders parasitized by acrocerid larvae usually do not exhibit changes in their habits, physiology or body shape due to parasitism for most of their life (Schlinger 1960). Clausen (1940) and Lamore (1960) noticed that the spider do not show any sign of parasitism until a few hours before its death. For this reason, it is presumably not possible to identify a parasitized spider if the larva is not in the final stage of its development. However, some authors suggested changes in the host’s behavior right before the larva left the spider body, when the spider started to walk in an erratic way, without a defined trajectory (Montgomery 1903; Johnson 1915). Montgomery (1903) reported changes in the way the spider constructed its web, stating that parasitized spiders construct weaker webs. Schlinger (1952) characterized a parasitized spider as nervous, stating that it executed jerky movements, followed by the production of silk and construction of a protective molting web. This web completely surrounded the spider, which adopted a position with the ventral side of the abdomen facing upwards, the same position adopted by the spider reared by us. Though it adopted a belly up position, which is indicative of molting, it did not complete the process.

Cady et al. (1993) conducted laboratory observations of Lasiodora klugi Koch and observed that the spiders scratched incessantly at the lateral portions of the abdomen with the legs, in the region where the parasitoid spiracular plates protruded through the spider’s integument. The authors also observed that the spider appeared dazed as it moved about its container, because it ran into the walls and could not walk a straight line. In addition, Cady et al. (1993) stated that parasitized spiders tend to be smaller and weigh less than others of similar length, and are generally paler in color. Another physical manifestation of parasitoid presence pointed out by the authors was a small black circular lesion, approximately 1 millimeter in diameter by 0.5 millimeter high, shaped like a truncate tubercle on the anterolateral dorsum of the abdomen, probably the site of larval fly spiracular attachment. The authors found that each spider showing such a scar ultimately had an acrocerid larva emerge from it. Other studies showed that a short time before the parasite emergence the spider started to act in a peculiar manner, walking spasmodically and often turning in place aimlessly (Montgomery 1903).

While kept in the laboratory, the juvenile host spider reared by us started to behave in a very unusual manner. The spider began to show wandering activity and an aggressive behavior, also producing strong and consistent stridulations. Perez-Miles et al. (2005) conducted a detailed experimental work on Acanthoscurria suina Pocock , and kept spiders for an extended period of time in the laboratory. The authors concluded that the production of stridulation is not part of the sexual behavior and suggested that it is probably a defensive reaction. Thus, the agitated behavior showed by the reared Acanthoscurria sternalis here is likely a result of irritation caused by the parasitism by Exetasis jujuyensis Gillung sp. nov.

Cady et al. (1993) found that after the capture of spiders, Exetasis eickstedtae larvae remained in hosts from 10 days to a few months. Alternatively, von Eickstedt (1971, 1974) reported larvae within captive spiders from 139 to 577 days. Schlinger (1987) suggested that the fly larvae remain in their theraphosid hosts for many years before emergence, although there is little quantitative data to support this conclusion. The female adult of Exetasis jujuyensis Gillung sp. nov. left its host approximately eight months after the spider’s capture. On the other hand, reported Exetasis eickstedtae pupation times varied from 27 to 60 days (Eickstedt 1971), and 41 days (Cady et al. 1993). Vellard (1934) reported that 26 days were required for the pupa of a species of Exetasis to become an adult. The female adult of Exetasis jujuyensis Gillung sp. nov. emerged 34 days after molting.

FIGURE 9. Exetasis jujuyensis Gillung sp. nov. recently emerged adult female. A. lateral view; B. dorsal view; C. anterior view.

Figures

FIGURE 2. Exetasis wings. A. E. brasiliensis Carrera; B. E. jujuyensis Gillung sp. nov.; C. E. calida Wiedemann (modified from Wiedemann 1830, plate VII, fig. 2 b). Scale line = 1 mm.

FIGURE 3. Exetasis jujuyensis Gillung sp. nov. A. lateral view; B. dorsal view.

FIGURE 4. Acanthoscurria sternalis, size of parasitoid’s emergence opening.

FIGURE 5. Acanthoscurria sternalis, dead spider showing the parasitoid’s emergence opening.

FIGURE 6. Exetasis jujuyensis Gillung sp. nov. larva attached to the spider tree trunk shelter.

FIGURE 7. Exetasis jujuyensis Gillung sp. nov. larva. A. lateral view; B. dorsolateral view, showing the pair of spiracles; C. dorsal view, showing the cephalic zone.

FIGURE 8. Exetasis jujuyensis Gillung sp. nov. pupa. A. dorsal view; B. lateral view.