Laboratory bioassay was carried out to study the insecticidal effect of 9 Croatian inert dusts against Sitophilus oryzae (L.) and to test their influence on bulk density of treated wheat. In order to compare effectiveness of Croatian inert dust samples, a standard USA diatomaceous earth (DE) Celatom® Mn 51, registered as an insecticide for stored-products protection, was used. Wheat kernels with approximately 13% moisture content were treated with inert dusts at doses 300, 400, 500 and 600 ppm and mortality of S. oryzae adults was assessed after 7 and 14 days and progeny after 49 days. The most effective Croatian inert dust samples were D-02B, D-01 and MA-4 with the LD90 values of 359.6, 447.2 and 458.7 ppm, respectively. In addition, effective dose that reduced F1 progeny in half was lower in regard to the other tested samples including the standard DE Mn 51, with the ED50 values 71.9, 54.6 and 137.6 ppm, respectively. According to the XRF analytical results, the highest amount of biogenic silica (BSi) was found in samples D-02B, D-01 and MA-4 (45.98, 35.09 and 21.28%, respectively). Paleontological data analysis confirmed diatoms species in only 5 samples of Croatian inert dusts (D-01, D-02B, PD-1, MA-4 and JU-1). All tested inert dusts affected reduction in bulk density of treated wheat at the LD90 concentrations, from 4.4 (D-02B) to 5.6 (JU-1) kg hL-1. More effective inert dusts at lower doses equally reduced bulk density as less effective inert dusts at much higher doses.

Croatian diatomites and their possible application as a natural insecticide

The genus Amphora sensu lato was considered highly heterogeneous for a long time. Modern microscopy and molecular analyses revealed significant differences in cell morphology and structure, thus suggesting polyphyly of the genus. New findings resulted in separation and description of several amphoroid genera. Recently, the genus Tetramphora Mereschkowsky was re-established based on ultrastructural and molecular analyses. The genus is widely spread in marine and brackish habitats. Recent observations of contemporary flora and cores from Lake Vransko (Croatia) revealed a new species of Tetramphora. The new species is characterized by having large semi-elliptical valves with arched dorsal margin and biarcuate ventral margin, length of 49.0–78.0 µm and width between 7.5–12.0 µm. The raphe is discontinuous, with proximal raphe ends externally covered with large siliceous flap. Striae are uniseriate, composed of small round to elongated areolae. Based on this unique combination of characters visible on light and scanning electron microscope, a new species Tetramphora croatica sp. nov. is described.