Constant seed size and mandible growth – a fundamental problem for granivorous ground beetle larvae (Coleoptera: Carabidae)

Paarmann,W.,Faust,N.,Arndt,E.,Luchtrath,I.&Rohe,W.2006:Constantseed size and mandible growth – a fundamental problem for granivorous ground beetle larvae (Coleoptera: Carabidae). — Entomol. Fennica 17: 334–339. Feeding on small tree seeds at fruit falls is a specific adaptation of harpaline ground beetles and their larvae in tropical rain forests. Using mandibles as tools, they havetoperforatetheseedshelltoreachthenutritiousinterior.Theisometric growth of larval mandibles, known from predatory species, would result in a changing ratio between seed and mandible size during the course of development. The stable size of host tree seeds should select an optimum mandible size, similar for the three larval instars in spermophageous species. We found an increasing tendency to maintain the length of the apical mandible part (apex) in seedfeedingspecies.ThesizeincreaseishigherinthespeciesfromAustralia,Africa and South East Asia than in the New World species of the genus Notiobia. Feedingexperimentshaverevealedthatlarvaeofspecieswithastrongerincrease inapexgrowtharealsoabletodevelopaspredatorsofDrosophilalarvae.Ourresultsfurthermorepointtoaninfluenceofbeetlesizeandshellhardnessofthehost tree seeds on the apex size and its growth rate.