Abstract:

Weevils are one of the largest groups of living organisms, with more than 60,000 species feeding mostly on plants.With only one exception, their described larvae are typical plant-feeders, with mouthparts adapted to chewing plant material. Here we describe the second case of a weevil with early-instar larvae adapted to killing conspecifics.We have studied the life history of Anchylorhynchus eriospathae G. G. Bondar, 1943 (Curculioninae:Derelomini sensu Caldara, Franz&Oberprieler (2014)), a species whose immatures feed internally on palm flowers and fruits.We provide detailed descriptions of all immature stages, including the extremely modi- fied first-instar larva. Unlike other weevils and later instars, this stage exhibits a flat bodywith very long ventropedal lobe setae, a large and prognathous headwith a gula, and falciformmandibles, eachwith a serrate retinaculum, that are used to fightwith and eventually kill other first-instar larvae.We also provide biological notes on all stages and the results of behavioral tests that showed that larval aggression occurs only among early life stages. Finally we show that adult size is highly dependent on timing of oviposition. This specialized killer first instar probably evolved indepen- dently fromthe one other case known inweevils, in Revena rubiginosa (Conoderinae: Bariditae sensu Prena, Colonnelli&Hespenheide (2014)). Interestingly, both lineages inhabit the same hosts, raising the possibility that both intra- and inter-specific competition shaped those phenotypes. Given the scarcity of knowledge on early larval stages of concealed insect herbivores, it is possible that our findings represent an instance of amuch broader phenomenon. Our observations also allowed us to conclude that Anchylorhynchus eriospathae and A. hatschbachi G. G. Bondar, 1943 are actually the same species,whichwe synonymize here by considering the latter as a junior synonym(newsynonymy).

Publisher's Version