Members of the pyrrole group are likely to have interesting properties that merit additional investigation as insecticides at the post-harvest stages of agricultural commodities. In the present work, the insecticidal effect of two new pyrrole derivatives, ethyl 3-(benzylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-carboxylate (3i) and isopropyl 3-(benzylthio)-4,6-dioxo-5-phenyl-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrrole-carboxylate (3k) were studied as stored-wheat protectants against two major stored-product insect species, the confused flour beetle, Tribolium confusum Jaquelin du Val adults and larvae and the Mediterranean flour moth, Ephestia kuehniella Zeller larvae at different doses (0.1, 1 and 10 ppm), exposure intervals (7, 14 and 21 days), temperatures (20, 25 and 30°C) and relative humidity (55 and 75%) levels. For T. confusum adults, in the case of the pyrrole derivative 3i, mortality was low and it did not exceed 32.2% in wheat treated with 10 ppm 3i at 30°C and 55% relative humidity. Progeny production was very low (<1 individual/vial) in all combinations of 55% relative humidity, including control. In the case of the pyrrole derivative 3k, mortality reached 67.8% at 30°C and 55% relative humidity in wheat treated with 10 ppm after 21 days of exposure. Progeny production was low in all tested combinations (≤0.7 individuals/vial) of 55% relative humidity, including control. For T. confusum larvae, in the case of the pyrrole derivative 3i, at the highest dose, mortality was 82.2% at 25°C and 55% relative humidity whereas in the case of 3k it reached 77.8% at the same combination. In contrast, mortality at 75% relative humidity remained very low and did not exceed 13.3%. For E. kuehniella larvae, the highest mortalities, 44.4 and 63.3%, were observed in 10 ppm at 25°C and 55% relative humidity for both pyrrole derivatives. The compounds tested here have a certain insecticidal effect, but this effect is moderated by the exposure, the target species, the temperature and the relative humidity.
Keywords: dose; exposure; pyrrole derivatives; relative humidity; stored-product insects; temperature.