Abstract
The rove beetle Triacrus dilatus is found in the Atlantic forest of South America and lives in the refuse piles of the paper wasp Agelaia vicina. Adults of T. dilatus are among the largest rove beetles, frequently measuring over 3 cm, and exhibit remarkable variation in body size. To examine sexual dimorphism and allometric relationships we measured the length of the left mandible, ocular distance and elytra. We were interested in determining if there are quantifiable differences between sexes, if there are major and minor forms within each sex and if males exhibit mandibular allometry. For all variables, a t-test was run to determine if there were significant differences between the sexes. Linear regressions were run to examine if there were significant relationships between the different measurements. A heterogeneity of slopes test was used to determine if there were significant differences between males and females. Our results indicated that males had significantly larger mandibles and ocular distances than females, but the overall body length was not significantly different between the sexes. Unlike most insects, both sexes showed positive linear allometric relationships for mandible length and head size (as measured by the ocular distance). We found no evidence of major and minor forms in either sex.
Highlights
The order Coleoptera, or beetles, is one of the most speciose lineages of all animals with more than 400,000 species described (Hammond, 1992)
While little is known about the behavior and natural history of xanthopygine beetles (Chatzimanolis, 2003; Chatzimanolis, 2014a), T. dilatus appears to have a fascinating natural history, occupying the nest refuse piles of the large paper wasp Agelaia vicina in the Atlantic forests of Brazil, Argentina and Paraguay (Wasmann, 1902; Kistner, 1982)
While many details on the natural history of T. dilatus are still lacking, it is possible that T. dilatus exhibits the same behavior as Quedius (Velleius) dilatatus (Fabricius), a central European species associated with paper wasps (Kistner, 1982)
Summary
The order Coleoptera, or beetles, is one of the most speciose lineages of all animals with more than 400,000 species described (Hammond, 1992). While many details on the natural history of T. dilatus are still lacking, it is possible that T. dilatus exhibits the same behavior as Quedius (Velleius) dilatatus (Fabricius), a central European species associated with paper wasps (Kistner, 1982). Both Q. dilatatus and T. dilatus have subserrate (asymmetrical, looking like marginal teeth-like structures pointing forward) antennae (visible on Fig. 3), which is often characteristic of rove beetles associated with social Hymenoptera (Schillhammer, 2013; Chatzimanolis, 2014b; Zhao & Zhou, 2015). According to zur Strassen (1957), Q. dilatatus is able to locate the paper wasps nests by following specific semiochemicals emitted by the wasps, and it is likely that T. dilatus can do the same
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