Philornis pici Macquart 1854

Philornis pici (Macquart, 1854)

Mason (1985) was the first to report botfly infestations in chicks of A. annumbi from Estancia El Talar (Buenos Aires, Partido Magdalena). These Philornis were not identified, but several years later Couri et al. (2005) cited Philornis seguyi García, 1952 as infesting other bird species from Partido Magdalena, 35º 08’ S, 57º 25’ W (Turienzo & Di Iorio 2007: table 2). The place cited by Couri et al. (2005) corresponds to Estancia El Destino, adjacent to Estancia San Isidro (Reboreda, pers. com.), Mason (1985) worked in both areas. By contrast, Nores (1993, 1995) cites P. p i c i, together with P. seguyi, infesting A. annumbi from Córdoba. In some cases both fly species were found on the same chick. Following the key of Couri (1999), specimens from Campo de Mayo were P. p i c i and not P. s e g u y i as was first suspected (Turienzo 2007; Turienzo & Di Iorio 2008).

Mason (1985) found botfly infestations in four (30.8 %) of 13 examined nests of A. annumb i, and these infestations were sufficient to kill all the young in one nest. From the province of Córdoba nine (13.8 %) of 65 nests were infested, with three to 17 larvae per chick (Nores 1993, 1995), whereas 12 (60 %) of 20 sampled nests from Campo de Mayo had puparia of Philornis.

In the earlier sampled nest 12-X-1992, 33 adults of P. p i c i emerged from two chicks of A. annumbi. One nest sampled in October 2005 (# 14) had two chicks of A. annumbi; one escaped and the second was infested with 10 larvae (3 larvae and 5 pupae fixed, and 2 larvae found at the bottom of the nest, fixed as pupae). Surprisingly, an additional 164 adults of P. p i c i emerged from living pupae located in the bed of the same nest, for a total of 174 specimens. Adults from this nest emerge as follows: 25-X-05, 1 ex.; 26-X-05, 3 exx.; 27-X-05, 16 exx.; 28-X-05, 6 exx.; 29-X-05, 14 exx.; 30-X-05, 7 exx.; 31-X-05, 4 exx.; 1-XI-05, 4 exx.; 2-XI-05, 12 exx.; 3-XI-05, 23 exx.; 4-XI-05, 33 exx.; 5/ 9-XI-05, 23 exx.; 10-XI-05, 9 exx.; 11-XI-05, 1 ex.; [without date]-05, 8 exx.

Nest # 17 (21-XII-05) was colonized by more than one individual inquiline (S. phryganophila). The original bed of A. annumbi, situated at the bottom, gave 94 emerged and 65 parasitized puparia. The pupal cocoons were of two ages: the older ones grey, the newer white. Inside the nest there were three additional beds: an old bed of the inquiline bird containing 242 emerged and 58 parasitized puparia (19.3 %); the second inquiline bed, younger than the first, had three eggs but no puparia, and the third, recently constructed (Fig. 5), contained three eggs and no puparia. When the nest was dissected an additional 50 emerged and 14 parasitized puparia were found at the bottom of the bag.

Two additional emergences were obtained from nests of A. annumbi from Campo de Mayo that were reconstructed and inhabited by S. phryganophila (Table 1). Nest # 18 (5-II-06) was inhabited by the inquiline bird three times: two beds had dead chicks (Fig. 6), with Philornis puparia [not counted], from which five adults of P. p i c i had emerged [no emergence data]; the third bed was older than the other two and had 89 emerged and 25 parasitized puparia (21.9 %); yet another 34 puparia (four parasitized) were found at the bottom of the bag when the nest was dissected. The second latest emergence (two adults, 12-III-06) was obtained from nest # 19 (26-II-06) inhabited by one inquiline (empty bed).

Shortly after the nest was collected, the same species of Philornis also emerged from a nest from Santa Fe (Table 1): 4-XII-06 (16 exx.), 6-XII-06 (2 exx.), and 7-XII-06 (35 exx.).

Percent parasitoidism on the puparia of Philornis was 11.5 % (nest # 4), 8.06 % (nest # 6), and 17.1 % (nest # 19), but from nests with living puparia (Table 2) no parasitic wasps were obtained. Couri et al. (2006) record two chalcidid wasps as parasitoids of puparia of Philornis, one from Trinidad and the other from Brazil (Rio de Janeiro).

Large numbers of puparia per nest or inquiline beds are possible in one breeding period of a bird because it was seen that each brood can sustain up to three or four cohorts of Philornis flies (Dudaniec & Kleindorfer 2006). A mating pair of A. annumbi can have a second brood, with five pairs in the same old nest and two pairs in new nests (Nores 1993). Thus the puparia counted in a single nest may correspond to the accumulation of those of more than one brood and more than one cohort per brood.

Teixeira (1999) published an extensive survey of the biology of species of Philornis. Although nothing is mentioned about the annual cycle, Teixeira (1999) wrote that “althought birds in Neotropics may show a clear tendency to present more extensive and less synchronised breeding season than those registered in higher latitudes, it seems reasonable to suppose that the availability of adequate hosts for the infestation of Philornis would be, at least during certain periods, lesser than in others. Such a question would raise the supposition that the pupae of those flies would suffer a diapause, ending up their development only with the arrival of a new breeding season for their hosts.”

As the breeding period of A. annumbi ends in mid-December (Mason 1985), it is probable that the subsequent generations of P. p i c i infest different bird species during the summer and provide the pupal stage in the autumn in the nest of a bird with a late breeding period. The fact is that the latter generations of Philornis were obtained during February after the breeding period of A. annumbi, thereby affecting any inquiline bird. These last adults to emerge in March require another bird host (not yet identified) after March in order to overwinter as pupae or pharate adults. Subsequently adults will emerge the following spring that will then infect the first brood of A. annumbi. No living pupae were found in any nest of A. annumbi during autumn or winter (Table 2), showing that other bird species function as a “bridge” to the following spring.