Results

Results

The examination of several Neotropical specimens of Hylobiina revealed the existence of two types of ventrite-femoral stridulatory systems within the subtribe; type 1 ( Figures 1–6 View FIGURES 1–15 , 16–19 View FIGURES 16–25 , 28–31 View FIGURES 26–31 ), found in the genus Heilus and type 2 ( Figures 7–15 View FIGURES 1–15 , 20–25 View FIGURES 16–25 ), found in a group of species currently placed within the genus Heilipodus . In both genera, these structures are present in both males and females.

Ventrite-femoral stridulatory system type 1. File is a basal fold of first ventrite strongly dilated behind the coxae, forming a more or less accentuated angle ( Figures 1–6 View FIGURES 1–15 ), and plectrum is associated with the inner face of the hind femur without perpendicular ridges ( Figures 16–19 View FIGURES 16–25 ). Heilipodus spinipennis (Champion 1906) is treated herein as Heilus spinipennis (Champion 1906) , comb. nov., for presenting the system type 1 structure ( Figures 26–31 View FIGURES 26–31 ).

Ventrite-femoral stridulatory system type 2. File is a basal fold of first ventrite behind the coxa, dilated more laterally than in type 1, posterior margin rounded ( Figures 7–15 View FIGURES 1–15 ), and plectrum is on the inner face of the hind femur with perpendicular ridges ( Figures 20–23 View FIGURES 16–25 ), except in Heilipodus naevulus ( Figures 24–25 View FIGURES 16–25 ).

Discussion

Prior to this work, the ventrite-femoral stridulatory system has been described for the Coleoptera families Carabidae ( Paussini : Paussina ), Scarabaeidae ( Cetoniinae and Rutelinae ), Heteroceridae and Curculionidae ( Gahan 1900; Lyal 1993; Di Giulio et al. 2014; Wessel 2016; Riedel 2017). Specifically, for Curculionidae , this type of system has been recognized in the tribe Cryptorhynchini (Molytinae) in the genera Sympedius Pascoe 1876 (group I), Nyphaeba Pascoe 1871 and Strattis Pascoe 1883 ( Lyal 1993; Devi et al. 2016; Riedel 2017). In none of these cases the use of this system for sound production has been demonstrated; however, given its morphological structure and similarity to the stridulatory structures found in other groups of Coleoptera where sound production has been observed, it is highly probable that it also fulfills this function.

In this study, the ventrite-femoral stridulatory system is recorded for the first time for the subtribe Hylobiina of the tribe Molytini , although it does not seem to be a homologous structure with that recorded in other taxa mentioned above, since it has differences in the structure and position of the file and the plectrum. Also, there is a discrepancy in the literature regarding the parts that correspond to the file and the plectrum. In the genus Sympedius (group I), Lyal (1993) referred to the structure associated to the first ventrite as a file and the structure on the inner surface of hind femur as a plectrum. Devi et al. (2016) made the opposite assignments for Strattis , which was probably an error, since the authors stated that they followed the terminology used by Lyal (1993). Later, Riedel (2017) recorded a ventrite-femoral stridulatory system for Nyphaeba , also based on the scheme proposed by Lyal (1993); in this case the structures were appropriately named.

Regarding the structural and/or positional differences of the file and the plectrum, in Sympedius (group I) the file is a striated area located in the lateral region, almost reaching the posterior margin of the first ventrite (for more details see figure 190 in Lyal 1993) and the plectrum is described as a sculpted area on the inner surface of the hind femur. In Strattis , using the nomenclature correctly, the file consists of ridges located on the latero-posterior portion of the first ventrite and the plectrum on the inner surface of the hind femur, as longitudinal ridges located in a transversal area clearly elevated or convex (for more details see figures 123–130, 133– 139 in Devi et al. 2016). In Nyphaeba the file is a row of short ridges located towards the sides of the first ventrite that reach the posterior margin, and the plectrum consists of several longitudinal ridges on the inner surface of the hind femur (for more detail see figures 5a, c–d in Riedel 2017).

In Heilus and the Heilipodus species group, both structures are different from those of the three genera previously mentioned. The file ( Figures 1–15 View FIGURES 1–15 , 28–29 View FIGURES 26–31 ) is associated with a basal fold of the first ventrite, which is located just behind the hind coxae. In Heilus it is more dilated towards the ventral part ( Type 1), it also has a variable number of oblique ridges and its posterior margin is angled ( Figures 1–6 View FIGURES 1–15 , 28–29 View FIGURES 26–31 ). In the Heilipodus species group the file is more dilated towards the lateral region ( Type 2), without ridges (except in He. naevulus ) and its posterior margin is rounded ( Figures 7–15 View FIGURES 1–15 ). It is important to note that the fold of the first ventrite behind the coxae is present in all species of Heilipodus , and in some cases, this fold may be laterally expanded, as in type 2, but does not become stridulatory ( Figures 32–33 View FIGURES 32–39 ). To avoid confusion between stridulatory and non-stridulatory folds, it is necessary to examine carefully the sculpture of the fold. If the sculpture is very superficial, it would indicate that the fold is not stridulatory, and vice versa. If the doubt persists, confirmation may be achieved by checking the presence or absence of the plectrum on the inner surface of the femur ( Figures 34–35 View FIGURES 32–39 ).

The plectrum ( Figures 16–25 View FIGURES 16–25 , 30–31 View FIGURES 26–31 ) is found in a similar position in both genera: on the inner surface of the hind femur, in the area before the widening. In Heilus it is made up of a group of longitudinal striations that are not located in an elevated area and lack ridges ( Figures 16–19 View FIGURES 16–25 , 28–29 View FIGURES 26–31 ). In the Heilipodus species group, it is easily recognizable as an elevated plate with longitudinal striations and ridges perpendicular to the striations, except in He. naevulus ( Figures 24–25 View FIGURES 16–25 ). It is important to note that although the plectrum in elytro-femoral (present in Arniticus ) and ventrite-femoral systems is located on the inner surface of the hind femur, its position and morphology differ. In Arniticus , the plectrum tends to be more circular or oval and is displaced toward the middle part of femur, sometimes located over the femoral widening ( Figures 36–39 View FIGURES 32–39 ). In contrast, in Heilus and Heilipodus , the plectrum is more rectangular and positioned closer to the base of the femur, sometimes extending up to just before the femoral widening, but never beyond ( Figures 16–25 View FIGURES 16–25 , 30–31 View FIGURES 26–31 ). Therefore, the plectrum in the elytro-femoral and ventrite-femoral stridulatory systems should not be considered homologous, but rather as independent characters in future phylogenetic studies. Finally, only 27 of the 124 recognized species of Heilipodus were available to assess this structure, and the remaining species should be examined to ensure proper placement and to better understand the phylogenetic utility of the ventrite-femoral stridulatory systems.