Systematics of the seed beetle genus Decellebruchus Borowiec, 1987 (Coleoptera, Bruchidae)

Abstract Keys to species, descriptions, synonymy, host plants, and geographical distributions are presented for the three species in the genus Decellebruchus (Borowiec 1987); of those, Decellebruchus walker (Pic 1912) was the only species included at the time of the genus denomination, Decellebruchus atrolineatus (Pic 1921) is transferred to this genus, and Decellebruchus lunae is described as a new species. The shortest and most parsimonious phylogenetic tree for genera with pectinate antennae had a length of 33, consistency index 87, and retention index 81.


Introduction
The monotypic genus Decellebruchus was erected by Borowiec in 1987 with the type species Decellebruchus walkeri (Pic 1912). This species has a complicated history, starting with Bruchus figuratus that was described by Walker (1859); however this was a homonym and then Pic (1912) proposed the replacement name of Bruchus walkeri. Later Decelle (1975b) transferred it to Bruchidius, but because the unusual pectinate antennae of the species in the genus Bruchidius, Borowiec (1987) erected the monotypic genus Decellebruchus for it. Another species that has been included unofficially in the latter genus is Bruchus atrolineatus Pic, 1921;however B. atrolineatus has also suffered a series of generic changes through time. Finally the third species included in the genus is the new species D. lunae. In order to clarify the genus it is reviewed and a hypothesis of its phylogeny is proposed.

Material and methods
Specimens. Preparation of genitalia for study followed the techniques and nomenclature described by Kingsolver (1970) and modified by Romero and Johnson (1999). For specimens the following collections were consulted: Colección Entomológica del Colegio de Postgraduados, Montecillo, Estado de México, México (CEAM), Florida Cladistics. External morphological characters and internal characters, these latter only from male genitalia (Table 1) were used. Host plants and distribution were also considered. Taxa included in the analysis were only those bruchids with pectinate antennae (excluding the genera Caryedes and Gibbobruchus because they have only few species with pectinate antennae) and all species in the genus Decellebruchus. Pachymerus, a less derived genus was used as the outgroup. The data matrix is presented in Table 2. The program Hennig86 (Farris 1988) was used to generate the cladogram, although a comparative tree was obtained with Mesquite, version 3.04 (Maddison and Maddison 2015) using the same data matrix.

Results and discussion
Key to genera of Bruchidae with pectinate antennae.
Host plant. Unknown.    Diagnosis. This species is included in the genus Decellebruchus because it presents all characters indicated in the diagnosis of the genus; also it can be separated from the other two species in the genus because the typical male pygidium, less strongly male antennae, unique armature of the internal sac of male genitalia, and lateral lobes of which bear a basal strut with a strong perpendicular keel.
Discussion. There is little information about this species. At this time its host plants are unknown and only a few specimens were available for study; three of which were still named Bruchidius walkeri.

Cladistics
A default tree (Fig. 13) and a consensus tree (Fig. 14) were generated with Mesquite (Maddison and Maddison 2015). The shortest and most parsimonius tree obtained with Henning86 using ie-algorithm is shown in Fig. 15. This tree was the shortest and the most parsimonious with a length of 33, consistency index of 87, and retention index of 81. In total, this cladogram was formed by 26 synapomorphies, 8 parallelisms, and 3 reversals. The tree generated with Hennig86 seems the most reliable to explain the phylogenetic hypothesis about of bruchids with pectinate antennae where males and females share the character; however, the consensus tree generated with Mesquite program has similarities with the Hennig86 tree.
In the cladogram in Figure 15 can be seen that each one of the clades corresponds to a different taxon of the family Bruchidae and one of the richest in terms of the number of genera was the Acanthoscelidini clade. This cladogram also supports the hypothesis of host preference, for example the species of the clade Pachymerini feed on seeds of the Arecaceae (palms), Megacerini on seeds of the Convolvulaceae, and Acanthoscelidini on seeds of the Fabaceae.