Trace metals in the ovipositors of wood-boring Hymenoptera

Metal-protein complexes involving zinc, manganese, and/or calcium help strengthen parts of the insect cuticle subject to extreme wear and tear. Relatively high concentrations of metals have been reported in the mandibles of numerous arthropod taxa and in the ovipositors of hymenopterans that must drill through wood to lay their eggs. We report on a novel method of assessing trace metal content in hymenopteran ovipositors that allows for quantitative comparisons between individuals and across taxa. Individual ovipositors of Sirex noctilio (Siricidae) were divided into millimetric pieces and dissolved for analysis by quadrupole inductively coupled plasma mass spectrometry (ICP-MS; Bruker 820MS). Multiple measurements revealed consistently high concentrations of Zn in ovipositor tips. Manganese is present but in abundances comparable to metals such as Ni, Fe, and Cu. The quantitative analyses were supplemented by high-resolution scans at the National Synchrotron Light Source at Brookhaven, New York, using synchrotron X-ray fluorescence to map trace metal distribution. These scans indicate that the Zn is concentrated in the cutting edges. Preliminary studies of the ovipositors of rhyssine ichneumonids indicate enrichment of the ovipositor tips with Mn and to a lesser extent Zn, with Ca more broadly distributed across the length of the structure.