A total of 8,384 specimens of Cryptinae were collected, of which 6,657 (79.4%) belonged to T. polita, and 1,727 (20.6%) to all other Cryptinae combined (Table 1). The overall sampling efficiency was 2.04. For T. polita alone, sampling efficiency was 1.62, and for all the other Cryptinae combined, 0.42. This quantitative superiority, however, was not uniform (Fig. 3). During the dry season (DS), T. polita represented only about 7% of the total Cryptinae collected. This situation was then drastically reversed in the rainy season (RS), when this ratio jumped to nearly 85%. The differences between dry and rainy seasons remain evident if the weekly totals are independently compared and are again clear if each week (Fig. 4) is compared separately, year by year.

Figure 3.  

Mean number of specimens per sample (total of 3 traps; 195 samples/8 years), with standard error bars, comparing T. polita (Tp) with other Cryptinae (Cr) in three successional areas, primary forest (PF), tall secondary forest (TSF), and low secondary forest (LSF) (left chart), and in the dry season (DS) vs. rainy season (RS) (right chart). PERD.

Figure 4.  

Total number of specimens collected in each sampling week (=each black & white bar pair, equivalent to 3 areas x 3 traps) for T. polita (white, first plane) vs. other Cryptinae (black, behind), along the sampled seasons (Day number of year, where DS=183–215, RS=286–322), discriminated for each year (0–1 = 2000–2008). Left wall (YZ axes) shows daily records of precipitation (cumulative values within each month), for all years (2893 records total); right wall (YX axes) shows average of precipitation for each Day number of year (each day = average of all years). Scale for number of specimens and precipitation (Y-axis) are identical.

For Cryptinae as a whole, sampling efficiency during the RS was 0.56, versus 0.25 in the DS, that is, 2.25× higher in the rainy season. The increase matches the observations of Kumagai (2002) for the Ichneumonidae in a preserved area in the Atlantic Forest, which tripled in number in the traps in the RS. This indicates that a two to threefold increase during the rainy season could be “normal” for Ichneumonidae as a whole. For T. polita, however, seasonal influence was higher by two orders of magnitude, with sampling efficiency rising from 0.02 in the DS to 2.92 in the RS – a 146× increase (Table 2).

The seasonal dominance of T. polita in the park was not a happenstance: it occurred repeatedly through the years (Fig. 4), as evidenced by its nearly uninterrupted numerical superiority in the samples (Table 3), and by its presence in 47.8% of the individual trap samples from the RS, against only 9.2% for the DS.

There was a distinctive quantitative difference among the three successional areas for the occurrence of both T. polita and other Cryptinae (Table 1). All differences discussed next are statistically significant (see confidence interval bars in Fig. 3). For other Cryptinae, the primary forest (PF) area had the highest abundance (871 specimens, 50.4% of the total), closely followed by the tall secondary forest (TSF) (710; 41.1%) and low secondary forest (LSF) (146; 8.5%). For T. polita, however, the TSF supported a much higher number of specimens (4,691; 70.5%), followed by the PF (1,956; 29.4%). The LSF was clearly avoided by this species, with only 10 specimens collected there throughout the study (0.15%).

Parasitoid wasps in general are most abundant in the rainy season, as compared to dry periods (Gauld 1991). However, this relationship remains insufficiently discussed and documented in the literature. The high level of dominance documented for T. polita has never been reported for any species of Ichneumonidae in natural areas, representing a noteworthy fact by itself. Previous faunistic studies of ichneumonid wasps in the Neotropics (e.g. Aguiar and Santos 2010; Guerra and Penteado-Dias 2002; Kumagai and Graf 2000; Kumagai and Graf 2000; Saaksjarvi et al. 2004) have never report any species as particularly dominating the collected samples. Considering that studies at the species level are scant for Ichneumonidae, the case for T. polita becomes of further interest, both because it is a rare study and because it signals that there is much still to be gained from studies on ichneumonid ecology.

The notorious success of T. polita in the tall secondary forest, as well as its distinct population dynamics in relation to other Cryptinae, suggest it may naturally act as a large-scale parasitoid in intermediate successional stages. This might also reveal to be of more general interest, now or in the future: this type of forest is predicted to increase in the 21st century due to industrialization and urbanization (Thomlinson et al. 1996), and yet, "there is still a tremendous need to understand and further refine our knowledge of ecological processes involved in secondary succession" (Guariguata and Ostertag 2001).