Elemental concentrations in the frass of saproxylic insects suggest a role in micronutrient cycling

Concentrations of 22 elements in pinewood were compared with that in frass produced by insects representing the following taxa: Reticulitermes spp. (Rhinotermitidae), Zootermopsis nevadensis (Termopsidae), Incisitermes snyderi (Kalotermitidae), Hylotrupes spp. (Cerambycidae), Heterobostrychus spp. (Bostrichidae), Lyctus spp. (Bostrichidae), and representatives of the family Ptinidae (formerly Anobiidae). Twenty elements (Al, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Si, Sr, and Zn) were measured using inductively coupled plasmaoptical emission spectroscopy (ICPOES), whereas carbon, hydrogen, and nitrogen percentages were measured using a CHN autoanalyzer. Chromium was the only element present at a statistically lower concentration in all frass types compared to pinewood. A comparison of pinewood to frass from those taxa that fed on pine revealed that Reticulitermes frass contained significantly higher levels of 15 elements, Zootermopsis 10, Ptinidae 5, Incisitermes 4, and Hylotrupes 1. Only Incisitermes frass showed a significantly higher percent carbon than pinewood and Reticulitermes, Zootermopsis, and Ptinidae showed significantly higher percent nitrogen. Examination of percent approximate digestibility (PAD) indicated that Reticulitermes frass had 14 elements that were ≥200% more concentrated than found in pinewood, whereas Zootermopsis had 6, Lyctus 5, ptinid 4, Hylotrupes and Heterobostrychus 3, and Incisitermes none. This survey of elements in frass indicates that saproxylic insects are, for the most part, not sequestrating but rather recycling (releasing) the store of micronutrients in wood biomass, with the greatest potential contribution to soil nutrient cycles attributable to subterranean termites.